| Message ID | 20170918072139.6300-8-quwenruo.btrfs@gmx.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the filesystem, > +prevent user to make use of the remaining space. > +In v4.14 btrfs-progs, this behavior is changed, and will not shrink the fs. > +The result should be the same as `mkfs`, `mount` and then `cp -r`. + Hmm well. Shrink to fit exactly to the size of the given files-and-directory is indeed a nice feature. Which would help to create a golden-image btrfs seed device. Its not popular as of now, but at some point it may in the cloud environment. Replacing this feature instead of creating a new option is not a good idea indeed. I missed something ? Thanks, Anand > +Also, if destination file/block device does not exist, *--rootdir* will not > +create the image file, to make it follow the normal mkfs behavior. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
As I already stated in an other thread, if you want to shrink, do it in another command line tool. Do one thing and do it simple. (Although Btrfs itself is already out of the UNIX way) It may be offline shrink/balance. But not to further complexing the --rootdir option now. And you also said that, the shrink feature is not a popular feature *NOW*, then I don't think it's worthy to implment it *NOW* either. Implement future feature in the future please. And further more, even following the existing shrink behavior, you still need to truncate the file all by yourself. Which is no better than creating a good sized file and then mkfs on it. Thanks, Qu Sent: Friday, September 22, 2017 at 5:24 PM From: "Anand Jain" <anand.jain@oracle.com> To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org Cc: dsterba@suse.cz Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra condition for rootdir option > +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the filesystem, > +prevent user to make use of the remaining space. > +In v4.14 btrfs-progs, this behavior is changed, and will not shrink the fs. > +The result should be the same as `mkfs`, `mount` and then `cp -r`. + Hmm well. Shrink to fit exactly to the size of the given files-and-directory is indeed a nice feature. Which would help to create a golden-image btrfs seed device. Its not popular as of now, but at some point it may in the cloud environment. Replacing this feature instead of creating a new option is not a good idea indeed. I missed something ? Thanks, Anand > +Also, if destination file/block device does not exist, *--rootdir* will not > +create the image file, to make it follow the normal mkfs behavior. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017-09-22 06:39, Qu Wenruo wrote: > As I already stated in an other thread, if you want to shrink, do it in another command line tool. > Do one thing and do it simple. (Although Btrfs itself is already out of the UNIX way) Unless I'm reading the code wrong, the shrinking isn't happening in a second pass, so this _is_ doing one thing, and it appears to be doing it as simply as possible (although arguably not correctly because of the 1MB reserved area being used). > > It may be offline shrink/balance. But not to further complexing the --rootdir option now. > > And you also said that, the shrink feature is not a popular feature *NOW*, then I don't think it's worthy to implment it *NOW* either. > Implement future feature in the future please. I'm not sure about you, but I could have sworn that he meant seed devices weren't a popular feature right now, not that the shrinking is. As a general rule, the whole option of pre-loading a filesystem with data as you're creating it is not a popular feature, because most sysadmins are much more willing to trust adding data after the filesystem is created. Personally, given the existence of seed devices, I would absolutely expect there to be a quick and easy way to generate a minimalistic image using a single command (because realistic usage of seed devices implies minimalistic images). I agree that it shouldn't be the default behavior, but I don't think it needs to be removed completely. The main issues here are that it wasn't documented well (like many other things in BTRFS), and it didn't generate a filesystem that was properly compliant with the on-disk format (because it used space in the 1MB reserved area at the beginning of the FS). Fixing those issues in no way requires removing the feature. > > And further more, even following the existing shrink behavior, you still need to truncate the file all by yourself. > Which is no better than creating a good sized file and then mkfs on it. Only if you pre-create the file. If the file doesn't exist, it gets created at the appropriate size. That's part of why the chunk allocations are screwed up and stuff gets put in the first 1MB, it generates the FS on-the-fly and writes it out as it's generating it. > > Thanks, > Qu > > Sent: Friday, September 22, 2017 at 5:24 PM > From: "Anand Jain" <anand.jain@oracle.com> > To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org > Cc: dsterba@suse.cz > Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra condition for rootdir option > >> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the filesystem, >> +prevent user to make use of the remaining space. >> +In v4.14 btrfs-progs, this behavior is changed, and will not shrink the fs. >> +The result should be the same as `mkfs`, `mount` and then `cp -r`. + > > Hmm well. Shrink to fit exactly to the size of the given > files-and-directory is indeed a nice feature. Which would help to create > a golden-image btrfs seed device. Its not popular as of now, but at some > point it may in the cloud environment. > > Replacing this feature instead of creating a new option is not a good > idea indeed. I missed something ? > > Thanks, Anand > >> +Also, if destination file/block device does not exist, *--rootdir* will not >> +create the image file, to make it follow the normal mkfs behavior. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017年09月22日 19:38, Austin S. Hemmelgarn wrote: > On 2017-09-22 06:39, Qu Wenruo wrote: >> As I already stated in an other thread, if you want to shrink, do it >> in another command line tool. >> Do one thing and do it simple. (Although Btrfs itself is already out >> of the UNIX way) > Unless I'm reading the code wrong, the shrinking isn't happening in a > second pass, so this _is_ doing one thing, and it appears to be doing it > as simply as possible (although arguably not correctly because of the > 1MB reserved area being used). If you're referring to my V1 implementation of shrink, that's doing *one* thing. But the original shrinking code? Nope, or we won't have the custom chunk allocator at all. What I really mean is, if one wants to shrink, at least don't couple the shrink code into "mkfs.btrfs". Do shrink in its own tool/subcommand, not in a really unrelated tool. >> >> It may be offline shrink/balance. But not to further complexing the >> --rootdir option now. > >> And you also said that, the shrink feature is not a popular feature >> *NOW*, then I don't think it's worthy to implment it *NOW* either. >> Implement future feature in the future please. > I'm not sure about you, but I could have sworn that he meant seed > devices weren't a popular feature right now, Oh, sorry for my misunderstanding. > not that the shrinking is. > As a general rule, the whole option of pre-loading a filesystem with > data as you're creating it is not a popular feature, because most > sysadmins are much more willing to trust adding data after the > filesystem is created. > > Personally, given the existence of seed devices, I would absolutely > expect there to be a quick and easy way to generate a minimalistic image > using a single command (because realistic usage of seed devices implies > minimalistic images). I agree that it shouldn't be the default > behavior, but I don't think it needs to be removed completely. Just like I said in cover letter, even for ext*, it's provided by genext2fs, not mke2fs. I totally understand end-user really want a do-it-all solution. But from developers' view, the old UNIX way is better to maintain code clean and easy to read. In fact, you can even create your script to do the old behavior if you don't care that the result may not fully take use of the space, just by: 1) Calculate the size of the whole directory "du" command can do it easily, and it does things better than us! For years! 2) Multiple the value according to the meta/data profile Take care of small files, which will be inlined. And don't forget size for data checksum. (BTW, there is no way to change the behavor of inlined data and data checksum for mkfs. unlike btrfs-convert) 3) Create a file with size calculated by step 2) 4) Execute "mkfs.btrfs -d <dir> <created file>" > The main > issues here are that it wasn't documented well (like many other things > in BTRFS), and it didn't generate a filesystem that was properly > compliant with the on-disk format (because it used space in the 1MB > reserved area at the beginning of the FS). Fixing those issues in no > way requires removing the feature. Yes, 1MB can be fixed easily (although not properly). But the whole customized chunk allocator is the real problem. The almost dead code is always bug-prone. Replace it with updated generic chunk allocator is the way to avoid later whac-a-mole, and should be done asap. >> >> And further more, even following the existing shrink behavior, you >> still need to truncate the file all by yourself. >> Which is no better than creating a good sized file and then mkfs on it. > Only if you pre-create the file. If the file doesn't exist, it gets > created at the appropriate size. That's part of why the chunk > allocations are screwed up and stuff gets put in the first 1MB, it > generates the FS on-the-fly and writes it out as it's generating it. Nope, even you created the file in advance, it will still occupy the first 1M. BTW, you can get back the size calculation for shrink, but you will soon find that it's just the start of a new nightmare. Because there is no easy way to calculate the real metadata usage. The result (and the old calculator) will be no better than guessing it. (Well, just multiply the dir size by 2 will never go wrong) Thanks, Qu >> >> Thanks, >> Qu >> >> Sent: Friday, September 22, 2017 at 5:24 PM >> From: "Anand Jain" <anand.jain@oracle.com> >> To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org >> Cc: dsterba@suse.cz >> Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra >> condition for rootdir option >> >>> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the >>> filesystem, >>> +prevent user to make use of the remaining space. >>> +In v4.14 btrfs-progs, this behavior is changed, and will not shrink >>> the fs. >>> +The result should be the same as `mkfs`, `mount` and then `cp -r`. + >> >> Hmm well. Shrink to fit exactly to the size of the given >> files-and-directory is indeed a nice feature. Which would help to create >> a golden-image btrfs seed device. Its not popular as of now, but at some >> point it may in the cloud environment. >> >> Replacing this feature instead of creating a new option is not a good >> idea indeed. I missed something ? >> >> Thanks, Anand >> >>> +Also, if destination file/block device does not exist, *--rootdir* >>> will not >>> +create the image file, to make it follow the normal mkfs behavior. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017-09-22 08:32, Qu Wenruo wrote: > On 2017年09月22日 19:38, Austin S. Hemmelgarn wrote: >> On 2017-09-22 06:39, Qu Wenruo wrote: >>> As I already stated in an other thread, if you want to shrink, do it >>> in another command line tool. >>> Do one thing and do it simple. (Although Btrfs itself is already out >>> of the UNIX way) >> Unless I'm reading the code wrong, the shrinking isn't happening in a >> second pass, so this _is_ doing one thing, and it appears to be doing >> it as simply as possible (although arguably not correctly because of >> the 1MB reserved area being used). > > If you're referring to my V1 implementation of shrink, that's doing > *one* thing. > > But the original shrinking code? Nope, or we won't have the custom chunk > allocator at all. > > What I really mean is, if one wants to shrink, at least don't couple the > shrink code into "mkfs.btrfs". > > Do shrink in its own tool/subcommand, not in a really unrelated tool. There are two cases for shrinking a filesystem: 1. You're resizing it to move to a smaller disk (or speed up copying to another disk). 2. You're generating a filesystem image that needs to be as small as possible. Case 1 is obviously unrelated to creating a filesystem. Case 2 however is kind of integral to the creation of the filesystem image itself by definition, especially for a CoW filesystem because it's not possible to shrink to the absolute smallest size due to the GlobalReserve and other things. Similarly, there are two primary use cases for pre-loading the filesystem with data: 1. Avoiding a copy when reprovisioning storage on a system. For example, splitting a directory out to a new filesystem, you could use the -r option to avoid having to copy the data after mounting the filesystem. 2. Creating base images for systems. The first case shouldn't need the shrinking functionality, but the second is a very common use case together with the second usage for shrinking a filesystem. > >>> >>> It may be offline shrink/balance. But not to further complexing the >>> --rootdir option now. > >>> And you also said that, the shrink feature is not a popular feature >>> *NOW*, then I don't think it's worthy to implment it *NOW* either. >>> Implement future feature in the future please. >> I'm not sure about you, but I could have sworn that he meant seed >> devices weren't a popular feature right now, > > Oh, sorry for my misunderstanding. > >> not that the shrinking is. As a general rule, the whole option of >> pre-loading a filesystem with data as you're creating it is not a >> popular feature, because most sysadmins are much more willing to trust >> adding data after the filesystem is created. >> >> Personally, given the existence of seed devices, I would absolutely >> expect there to be a quick and easy way to generate a minimalistic >> image using a single command (because realistic usage of seed devices >> implies minimalistic images). I agree that it shouldn't be the >> default behavior, but I don't think it needs to be removed completely. > > Just like I said in cover letter, even for ext*, it's provided by > genext2fs, not mke2fs. Then maybe this should get split out into a separate tool instead of just removing it completely? There is obviously at least some interest in this functionality. > > I totally understand end-user really want a do-it-all solution. > But from developers' view, the old UNIX way is better to maintain code > clean and easy to read. What the code is doing should have near zero impact on readability. If it did, then the BTRFS code in general is already way beyond most people. > > > In fact, you can even create your script to do the old behavior if you > don't care that the result may not fully take use of the space, just by: > > 1) Calculate the size of the whole directory > "du" command can do it easily, and it does things better than us! For > years! Um, no it actually doesn't do things better in all cases. it doesn't account for extended attributes, or metadata usage, or any number of other things that factor into how much space a file or directory will take up on BTRFS. It's good enough for finding what's using most of your space, but it's not reliable for determining how much space you need to store that data (especially once you throw in in-line compression). > > 2) Multiple the value according to the meta/data profile > Take care of small files, which will be inlined. > And don't forget size for data checksum. > (BTW, there is no way to change the behavor of inlined data and data > checksum for mkfs. unlike btrfs-convert) This is where the issue lies. It's not possible for a person to calculate this with reasonable accuracy, and you arguably can't even do it for certain programmatically without some serious work. > > 3) Create a file with size calculated by step 2) > > 4) Execute "mkfs.btrfs -d <dir> <created file>" > >> The main issues here are that it wasn't documented well (like many >> other things in BTRFS), and it didn't generate a filesystem that was >> properly compliant with the on-disk format (because it used space in >> the 1MB reserved area at the beginning of the FS). Fixing those >> issues in no way requires removing the feature. > > Yes, 1MB can be fixed easily (although not properly). But the whole > customized chunk allocator is the real problem. > The almost dead code is always bug-prone. Replace it with updated > generic chunk allocator is the way to avoid later whac-a-mole, and > should be done asap. Agreed, but that doesn't preclude having the option to keep the generated image to the minimum size. > >>> >>> And further more, even following the existing shrink behavior, you >>> still need to truncate the file all by yourself. >>> Which is no better than creating a good sized file and then mkfs on it. >> Only if you pre-create the file. If the file doesn't exist, it gets >> created at the appropriate size. That's part of why the chunk >> allocations are screwed up and stuff gets put in the first 1MB, it >> generates the FS on-the-fly and writes it out as it's generating it. > > Nope, even you created the file in advance, it will still occupy the > first 1M. Because it doesn't assume that the file is there to begin with. It's not trying O_CREAT and falling back to some different code if that fails. The code assumes that the file won't be there, and handles things accordingly albeit incorrectly (it should seek past the first 1MB, write the initial SB, and then start chunk allocation). IOW, the code takes a shortcut in that it doesn't check for the file, and the rest is written to account for that by assuming there wasn't a file. The lack of truncation just means it doesn't try to trim things down by itself if the file is already there (it assumes that you knew what you were doing). Put differently, I'm fairly certain that the current -r option removes the total size check unless the target is a device (although it may remove the check there too and just fail when it tries to write past the end of the device), and will thus extend existing files to the required size to hold the data. > > BTW, you can get back the size calculation for shrink, but you will soon > find that it's just the start of a new nightmare. > Because there is no easy way to calculate the real metadata usage. > > The result (and the old calculator) will be no better than guessing it. > (Well, just multiply the dir size by 2 will never go wrong) No, it can go wrong depending on what you count as part of the size. > > > Thanks, > Qu > >>> >>> Thanks, >>> Qu >>> >>> Sent: Friday, September 22, 2017 at 5:24 PM >>> From: "Anand Jain" <anand.jain@oracle.com> >>> To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org >>> Cc: dsterba@suse.cz >>> Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra >>> condition for rootdir option >>> >>>> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the >>>> filesystem, >>>> +prevent user to make use of the remaining space. >>>> +In v4.14 btrfs-progs, this behavior is changed, and will not shrink >>>> the fs. >>>> +The result should be the same as `mkfs`, `mount` and then `cp -r`. + >>> >>> Hmm well. Shrink to fit exactly to the size of the given >>> files-and-directory is indeed a nice feature. Which would help to create >>> a golden-image btrfs seed device. Its not popular as of now, but at some >>> point it may in the cloud environment. >>> >>> Replacing this feature instead of creating a new option is not a good >>> idea indeed. I missed something ? >>> >>> Thanks, Anand >>> >>>> +Also, if destination file/block device does not exist, *--rootdir* >>>> will not >>>> +create the image file, to make it follow the normal mkfs behavior. >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017年09月22日 21:33, Austin S. Hemmelgarn wrote: > On 2017-09-22 08:32, Qu Wenruo wrote: >> On 2017年09月22日 19:38, Austin S. Hemmelgarn wrote: >>> On 2017-09-22 06:39, Qu Wenruo wrote: >>>> As I already stated in an other thread, if you want to shrink, do it >>>> in another command line tool. >>>> Do one thing and do it simple. (Although Btrfs itself is already out >>>> of the UNIX way) >>> Unless I'm reading the code wrong, the shrinking isn't happening in a >>> second pass, so this _is_ doing one thing, and it appears to be doing >>> it as simply as possible (although arguably not correctly because of >>> the 1MB reserved area being used). >> >> If you're referring to my V1 implementation of shrink, that's doing >> *one* thing. >> >> But the original shrinking code? Nope, or we won't have the custom >> chunk allocator at all. >> >> What I really mean is, if one wants to shrink, at least don't couple >> the shrink code into "mkfs.btrfs". >> >> Do shrink in its own tool/subcommand, not in a really unrelated tool. > There are two cases for shrinking a filesystem: > 1. You're resizing it to move to a smaller disk (or speed up copying to > another disk). > 2. You're generating a filesystem image that needs to be as small as > possible. I would argue there is no meaning of creating *smallest* image. (Of course it exists) We could put tons of code to implement, and more (or less) test cases to verify it. But the demand doesn't validate the effort. All my points are clear for this patchset: I know I removed one function, and my reason is: 1) No or little usage And it's anti intuition. 2) Dead code (not tested nor well documented) 3) Possible workaround I can add several extra reasons as I stated before, but number of reasons won't validate anything anyway. Building software is always trading one thing for another. I understand there may be some need for this function, but it doesn't validate the cost. And I think the fact that until recently a mail reported about the shrinking behavior has already backed up my point. Thanks, Qu > > Case 1 is obviously unrelated to creating a filesystem. Case 2 however > is kind of integral to the creation of the filesystem image itself by > definition, especially for a CoW filesystem because it's not possible to > shrink to the absolute smallest size due to the GlobalReserve and other > things. > > Similarly, there are two primary use cases for pre-loading the > filesystem with data: > 1. Avoiding a copy when reprovisioning storage on a system. For > example, splitting a directory out to a new filesystem, you could use > the -r option to avoid having to copy the data after mounting the > filesystem. > 2. Creating base images for systems. > > The first case shouldn't need the shrinking functionality, but the > second is a very common use case together with the second usage for > shrinking a filesystem. >> >>>> >>>> It may be offline shrink/balance. But not to further complexing the >>>> --rootdir option now. > >>>> And you also said that, the shrink feature is not a popular feature >>>> *NOW*, then I don't think it's worthy to implment it *NOW* either. >>>> Implement future feature in the future please. >>> I'm not sure about you, but I could have sworn that he meant seed >>> devices weren't a popular feature right now, >> >> Oh, sorry for my misunderstanding. >> >>> not that the shrinking is. As a general rule, the whole option of >>> pre-loading a filesystem with data as you're creating it is not a >>> popular feature, because most sysadmins are much more willing to >>> trust adding data after the filesystem is created. >>> >>> Personally, given the existence of seed devices, I would absolutely >>> expect there to be a quick and easy way to generate a minimalistic >>> image using a single command (because realistic usage of seed devices >>> implies minimalistic images). I agree that it shouldn't be the >>> default behavior, but I don't think it needs to be removed completely. >> >> Just like I said in cover letter, even for ext*, it's provided by >> genext2fs, not mke2fs. > Then maybe this should get split out into a separate tool instead of > just removing it completely? There is obviously at least some interest > in this functionality. >> >> I totally understand end-user really want a do-it-all solution. >> But from developers' view, the old UNIX way is better to maintain code >> clean and easy to read. > What the code is doing should have near zero impact on readability. If > it did, then the BTRFS code in general is already way beyond most people. >> >> >> In fact, you can even create your script to do the old behavior if you >> don't care that the result may not fully take use of the space, just by: >> >> 1) Calculate the size of the whole directory >> "du" command can do it easily, and it does things better than us! For >> years! > Um, no it actually doesn't do things better in all cases. it doesn't > account for extended attributes, or metadata usage, or any number of > other things that factor into how much space a file or directory will > take up on BTRFS. It's good enough for finding what's using most of > your space, but it's not reliable for determining how much space you > need to store that data (especially once you throw in in-line compression). >> >> 2) Multiple the value according to the meta/data profile >> Take care of small files, which will be inlined. >> And don't forget size for data checksum. >> (BTW, there is no way to change the behavor of inlined data and data >> checksum for mkfs. unlike btrfs-convert) > This is where the issue lies. It's not possible for a person to > calculate this with reasonable accuracy, and you arguably can't even do > it for certain programmatically without some serious work. >> >> 3) Create a file with size calculated by step 2) >> >> 4) Execute "mkfs.btrfs -d <dir> <created file>" >> >>> The main issues here are that it wasn't documented well (like many >>> other things in BTRFS), and it didn't generate a filesystem that was >>> properly compliant with the on-disk format (because it used space in >>> the 1MB reserved area at the beginning of the FS). Fixing those >>> issues in no way requires removing the feature. >> >> Yes, 1MB can be fixed easily (although not properly). But the whole >> customized chunk allocator is the real problem. >> The almost dead code is always bug-prone. Replace it with updated >> generic chunk allocator is the way to avoid later whac-a-mole, and >> should be done asap. > Agreed, but that doesn't preclude having the option to keep the > generated image to the minimum size. >> >>>> >>>> And further more, even following the existing shrink behavior, you >>>> still need to truncate the file all by yourself. >>>> Which is no better than creating a good sized file and then mkfs on it. >>> Only if you pre-create the file. If the file doesn't exist, it gets >>> created at the appropriate size. That's part of why the chunk >>> allocations are screwed up and stuff gets put in the first 1MB, it >>> generates the FS on-the-fly and writes it out as it's generating it. >> >> Nope, even you created the file in advance, it will still occupy the >> first 1M. > Because it doesn't assume that the file is there to begin with. It's > not trying O_CREAT and falling back to some different code if that > fails. The code assumes that the file won't be there, and handles > things accordingly albeit incorrectly (it should seek past the first > 1MB, write the initial SB, and then start chunk allocation). IOW, the > code takes a shortcut in that it doesn't check for the file, and the > rest is written to account for that by assuming there wasn't a file. The > lack of truncation just means it doesn't try to trim things down by > itself if the file is already there (it assumes that you knew what you > were doing). > > Put differently, I'm fairly certain that the current -r option removes > the total size check unless the target is a device (although it may > remove the check there too and just fail when it tries to write past the > end of the device), and will thus extend existing files to the required > size to hold the data. >> >> BTW, you can get back the size calculation for shrink, but you will >> soon find that it's just the start of a new nightmare. >> Because there is no easy way to calculate the real metadata usage. >> >> The result (and the old calculator) will be no better than guessing it. >> (Well, just multiply the dir size by 2 will never go wrong) > No, it can go wrong depending on what you count as part of the size. >> >> >> Thanks, >> Qu >> >>>> >>>> Thanks, >>>> Qu >>>> >>>> Sent: Friday, September 22, 2017 at 5:24 PM >>>> From: "Anand Jain" <anand.jain@oracle.com> >>>> To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org >>>> Cc: dsterba@suse.cz >>>> Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra >>>> condition for rootdir option >>>> >>>>> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the >>>>> filesystem, >>>>> +prevent user to make use of the remaining space. >>>>> +In v4.14 btrfs-progs, this behavior is changed, and will not >>>>> shrink the fs. >>>>> +The result should be the same as `mkfs`, `mount` and then `cp -r`. + >>>> >>>> Hmm well. Shrink to fit exactly to the size of the given >>>> files-and-directory is indeed a nice feature. Which would help to >>>> create >>>> a golden-image btrfs seed device. Its not popular as of now, but at >>>> some >>>> point it may in the cloud environment. >>>> >>>> Replacing this feature instead of creating a new option is not a good >>>> idea indeed. I missed something ? >>>> >>>> Thanks, Anand >>>> >>>>> +Also, if destination file/block device does not exist, *--rootdir* >>>>> will not >>>>> +create the image file, to make it follow the normal mkfs behavior. >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe >>> linux-btrfs" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> All my points are clear for this patchset: > I know I removed one function, and my reason is: > 1) No or little usage > And it's anti intuition. > 2) Dead code (not tested nor well documented) > 3) Possible workaround > > I can add several extra reasons as I stated before, but number of > reasons won't validate anything anyway. End user convenience wins over the developer's technical difficulties. Pls don't remove this feature, it needs fix such as #2 (above) to improve on #1 (above) as in your list. Thanks, Anand -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 09/24/2017 12:10 PM, Anand Jain wrote: > > >> All my points are clear for this patchset: >> I know I removed one function, and my reason is: >> 1) No or little usage >> And it's anti intuition. >> 2) Dead code (not tested nor well documented) >> 3) Possible workaround >> >> I can add several extra reasons as I stated before, but number of reasons won't validate anything anyway. > > End user convenience wins over the developer's technical difficulties. Sorry, but I have to agree with Qu; there is no a big demand (other than Austin) for this functionality; even you stated that "...at some point it may..."; until now the UI is quite unfriendly (we should use a big enough device, and then cut it by hand on the basis of the output of mkfs.btrfs)... I fear that this is another feature which increase the complexity of btrfs (and tools) with little or none usage.... The work of Qu is a nice cleanup; I hope that this will be the direction which BTRFS will takes: removing of "strange/unused" features improving the reliability of the others. BR G.Baroncelli > > Pls don't remove this feature, it needs fix such as #2 (above) to improve on #1 (above) as in your list. > > Thanks, Anand > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
On 2017-09-24 10:08, Goffredo Baroncelli wrote: > On 09/24/2017 12:10 PM, Anand Jain wrote: >> >> >>> All my points are clear for this patchset: >>> I know I removed one function, and my reason is: >>> 1) No or little usage >>> And it's anti intuition. >>> 2) Dead code (not tested nor well documented) >>> 3) Possible workaround >>> >>> I can add several extra reasons as I stated before, but number of reasons won't validate anything anyway. >> >> End user convenience wins over the developer's technical difficulties. > > Sorry, but I have to agree with Qu; there is no a big demand (other than Austin) for this functionality; even you stated that "...at some point it may..."; until now the UI is quite unfriendly (we should use a big enough device, and then cut it by hand on the basis of the output of mkfs.btrfs)... I will comment that I agree that it should not be the default. It's not intuitive for most people, and as you say it's a niche feature. Just removing it completely though with the above argument sounds very much like trying to meet quotas for coding. > > I fear that this is another feature which increase the complexity of btrfs (and tools) with little or none usage.... On average? It only increases the complexity of mkfs once there's a fix for the (theoretically trivial to fix) issue with it ignoring the fact that the first 1MB of space is supposed to be untouched by BTRFS. > > The work of Qu is a nice cleanup; I hope that this will be the direction which BTRFS will takes: removing of "strange/unused" features improving the reliability of the others. The two are not inherently interdependent, and that argument doesn't exactly hold up to scrutiny considering that mkfs is already perfectly reliable even with this feature, and it does not compromise the reliability of other features (again, once you fix the usage of the reserved area at the beginning of the image). -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017-09-22 11:07, Qu Wenruo wrote: > > > On 2017年09月22日 21:33, Austin S. Hemmelgarn wrote: >> On 2017-09-22 08:32, Qu Wenruo wrote: >>> On 2017年09月22日 19:38, Austin S. Hemmelgarn wrote: >>>> On 2017-09-22 06:39, Qu Wenruo wrote: >>>>> As I already stated in an other thread, if you want to shrink, do >>>>> it in another command line tool. >>>>> Do one thing and do it simple. (Although Btrfs itself is already >>>>> out of the UNIX way) >>>> Unless I'm reading the code wrong, the shrinking isn't happening in >>>> a second pass, so this _is_ doing one thing, and it appears to be >>>> doing it as simply as possible (although arguably not correctly >>>> because of the 1MB reserved area being used). >>> >>> If you're referring to my V1 implementation of shrink, that's doing >>> *one* thing. >>> >>> But the original shrinking code? Nope, or we won't have the custom >>> chunk allocator at all. >>> >>> What I really mean is, if one wants to shrink, at least don't couple >>> the shrink code into "mkfs.btrfs". >>> >>> Do shrink in its own tool/subcommand, not in a really unrelated tool. >> There are two cases for shrinking a filesystem: >> 1. You're resizing it to move to a smaller disk (or speed up copying >> to another disk). >> 2. You're generating a filesystem image that needs to be as small as >> possible. > > I would argue there is no meaning of creating *smallest* image. (Of > course it exists). There is an exact meaning given the on-disk layout. It's an image whose size is equal to the sum of: 1. 1MB (for the reserved space at the beginning). 2. However many superblocks it should have given the size. 3. The total amount of file data and extended attribute data to be included, rounding up for block size 4. The exact amount of metadata space needed to represent the tree from 3, also rounding up for block size. 5. The exact amount of system chunk space needed to handle 3 and 4, plus enough room to allocate at least one more chunk of each type (to ultimately allow for resizing the filesystem if desired). 6. Exactly enough reserved metadata space to resize the FS. > > We could put tons of code to implement, and more (or less) test cases to > verify it. > > But the demand doesn't validate the effort. And how much effort has been put into ripping this out completely together with the other fixes? How much more would it have been to just move it to another option and fix the reserved area usage? > > All my points are clear for this patchset: > I know I removed one function, and my reason is: > 1) No or little usage > And it's anti intuition. So split it to a separate tool (mkimage maybe?), and fix mkfs to behave sensibly. I absolutely agree on the fact that it's non-intuitive. It should either be it's own option (with a dependency on -r being passed of course), or a separate tool if you're so worried about mkfs being too complex. As to usage, given the current data, there is no proof that I'm the only one using it, but there is also no proof that anybody other than me is using it, which means that you can't reasonably base an argument on actual usage of this option, since you can't prove anything about usage. All you know is that you have one person who uses it, and one who was confused by it (but appears to want to use it in a different way). It's a niche use case though, and when dealing with something like this, there is a threshold of usage below which you won't see much in the way of discussion of the option on the list, since only a reasonably small percentage of BTRFS users are actually subscribed. > 2) Dead code (not tested nor well documented) <rant>It _IS NOT_ dead code. It is absolutely reachable from code external to itself. It's potentially unused code, but that is not the same thing as dead code.</rant> That aside, I can fix up the documentation, and I've actually tested it reasonably thoroughly (I use it every month or so when I update stuff I have using seed devices, and it also gets used by my testing infrastructure when generating images pre-loaded with files for tests to save time). I'll agree it hasn't been rigorously tested, but it does appear to work as (not) advertised, even when used in odd ways. > 3) Possible workaround There are three options for workarounds, and both of them are sub-par to this even aside from the reduced simplicity it offers to userspace: 1. Resize after mkfs. This is impractical both because there is no offline resize (having to mount the FS RW prior to use as a seed device means that you don't have a guaranteed reproducible image, which is a pretty common request for container usage there days), and it will end up with wasted space (the smallest possible filesystem created through a resize is consistently larger (by more than 1MB) than what the -r option to mkfs generates). 2. Use a binary search to determine the smallest size to a reasonable margin. This is impractical simply because it takes too long, and again can't reliably get the smallest possible image. 3. Attempt to compute the smallest possible image without using a binary search, pre-create the file, and then call mkfs. This is non-trivial without knowledge of the internal workings of mkfs, and is liable to break when something changes in mkfs (unless you want to consider the block-level layout generated by the --rootdir option to be part of the ABI and something that shouldn't change, but that is something you would need to discuss with the other developers). IOW, this is like saying that duct tape is a workaround for not having super glue. It will technically work, but not anywhere near as well. > > I can add several extra reasons as I stated before, but number of > reasons won't validate anything anyway. > > Building software is always trading one thing for another. > I understand there may be some need for this function, but it doesn't > validate the cost. > > And I think the fact that until recently a mail reported about the > shrinking behavior has already backed up my point. The only information it gives is that until now nobody who tried that option either cared enough to complain about it, or needed it to behave any other way. IOW, as stated above, given the current data, there is no proof that I'm the only one using it, but there is also no proof that anybody other than me is using it, which means that you can't reasonably base your argument on actual usage of this option. > > Thanks, > Qu > >> >> Case 1 is obviously unrelated to creating a filesystem. Case 2 >> however is kind of integral to the creation of the filesystem image >> itself by definition, especially for a CoW filesystem because it's not >> possible to shrink to the absolute smallest size due to the >> GlobalReserve and other things. >> >> Similarly, there are two primary use cases for pre-loading the >> filesystem with data: >> 1. Avoiding a copy when reprovisioning storage on a system. For >> example, splitting a directory out to a new filesystem, you could use >> the -r option to avoid having to copy the data after mounting the >> filesystem. >> 2. Creating base images for systems. >> >> The first case shouldn't need the shrinking functionality, but the >> second is a very common use case together with the second usage for >> shrinking a filesystem. >>> >>>>> >>>>> It may be offline shrink/balance. But not to further complexing the >>>>> --rootdir option now. > >>>>> And you also said that, the shrink feature is not a popular feature >>>>> *NOW*, then I don't think it's worthy to implment it *NOW* either. >>>>> Implement future feature in the future please. >>>> I'm not sure about you, but I could have sworn that he meant seed >>>> devices weren't a popular feature right now, >>> >>> Oh, sorry for my misunderstanding. >>> >>>> not that the shrinking is. As a general rule, the whole option of >>>> pre-loading a filesystem with data as you're creating it is not a >>>> popular feature, because most sysadmins are much more willing to >>>> trust adding data after the filesystem is created. >>>> >>>> Personally, given the existence of seed devices, I would absolutely >>>> expect there to be a quick and easy way to generate a minimalistic >>>> image using a single command (because realistic usage of seed >>>> devices implies minimalistic images). I agree that it shouldn't be >>>> the default behavior, but I don't think it needs to be removed >>>> completely. >>> >>> Just like I said in cover letter, even for ext*, it's provided by >>> genext2fs, not mke2fs. >> Then maybe this should get split out into a separate tool instead of >> just removing it completely? There is obviously at least some >> interest in this functionality. >>> >>> I totally understand end-user really want a do-it-all solution. >>> But from developers' view, the old UNIX way is better to maintain >>> code clean and easy to read. >> What the code is doing should have near zero impact on readability. >> If it did, then the BTRFS code in general is already way beyond most >> people. >>> >>> >>> In fact, you can even create your script to do the old behavior if >>> you don't care that the result may not fully take use of the space, >>> just by: >>> >>> 1) Calculate the size of the whole directory >>> "du" command can do it easily, and it does things better than us! >>> For >>> years! >> Um, no it actually doesn't do things better in all cases. it doesn't >> account for extended attributes, or metadata usage, or any number of >> other things that factor into how much space a file or directory will >> take up on BTRFS. It's good enough for finding what's using most of >> your space, but it's not reliable for determining how much space you >> need to store that data (especially once you throw in in-line >> compression). >>> >>> 2) Multiple the value according to the meta/data profile >>> Take care of small files, which will be inlined. >>> And don't forget size for data checksum. >>> (BTW, there is no way to change the behavor of inlined data and data >>> checksum for mkfs. unlike btrfs-convert) >> This is where the issue lies. It's not possible for a person to >> calculate this with reasonable accuracy, and you arguably can't even >> do it for certain programmatically without some serious work. >>> >>> 3) Create a file with size calculated by step 2) >>> >>> 4) Execute "mkfs.btrfs -d <dir> <created file>" >>> >>>> The main issues here are that it wasn't documented well (like many >>>> other things in BTRFS), and it didn't generate a filesystem that was >>>> properly compliant with the on-disk format (because it used space in >>>> the 1MB reserved area at the beginning of the FS). Fixing those >>>> issues in no way requires removing the feature. >>> >>> Yes, 1MB can be fixed easily (although not properly). But the whole >>> customized chunk allocator is the real problem. >>> The almost dead code is always bug-prone. Replace it with updated >>> generic chunk allocator is the way to avoid later whac-a-mole, and >>> should be done asap. >> Agreed, but that doesn't preclude having the option to keep the >> generated image to the minimum size. >>> >>>>> >>>>> And further more, even following the existing shrink behavior, you >>>>> still need to truncate the file all by yourself. >>>>> Which is no better than creating a good sized file and then mkfs on >>>>> it. >>>> Only if you pre-create the file. If the file doesn't exist, it gets >>>> created at the appropriate size. That's part of why the chunk >>>> allocations are screwed up and stuff gets put in the first 1MB, it >>>> generates the FS on-the-fly and writes it out as it's generating it. >>> >>> Nope, even you created the file in advance, it will still occupy the >>> first 1M. >> Because it doesn't assume that the file is there to begin with. It's >> not trying O_CREAT and falling back to some different code if that >> fails. The code assumes that the file won't be there, and handles >> things accordingly albeit incorrectly (it should seek past the first >> 1MB, write the initial SB, and then start chunk allocation). IOW, the >> code takes a shortcut in that it doesn't check for the file, and the >> rest is written to account for that by assuming there wasn't a file. >> The lack of truncation just means it doesn't try to trim things down >> by itself if the file is already there (it assumes that you knew what >> you were doing). >> >> Put differently, I'm fairly certain that the current -r option removes >> the total size check unless the target is a device (although it may >> remove the check there too and just fail when it tries to write past >> the end of the device), and will thus extend existing files to the >> required size to hold the data. >>> >>> BTW, you can get back the size calculation for shrink, but you will >>> soon find that it's just the start of a new nightmare. >>> Because there is no easy way to calculate the real metadata usage. >>> >>> The result (and the old calculator) will be no better than guessing it. >>> (Well, just multiply the dir size by 2 will never go wrong) >> No, it can go wrong depending on what you count as part of the size. >>> >>> >>> Thanks, >>> Qu >>> >>>>> >>>>> Thanks, >>>>> Qu >>>>> >>>>> Sent: Friday, September 22, 2017 at 5:24 PM >>>>> From: "Anand Jain" <anand.jain@oracle.com> >>>>> To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>, linux-btrfs@vger.kernel.org >>>>> Cc: dsterba@suse.cz >>>>> Subject: Re: [PATCH v3 07/14] btrfs-progs: Doc/mkfs: Add extra >>>>> condition for rootdir option >>>>> >>>>>> +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the >>>>>> filesystem, >>>>>> +prevent user to make use of the remaining space. >>>>>> +In v4.14 btrfs-progs, this behavior is changed, and will not >>>>>> shrink the fs. >>>>>> +The result should be the same as `mkfs`, `mount` and then `cp -r`. + >>>>> >>>>> Hmm well. Shrink to fit exactly to the size of the given >>>>> files-and-directory is indeed a nice feature. Which would help to >>>>> create >>>>> a golden-image btrfs seed device. Its not popular as of now, but at >>>>> some >>>>> point it may in the cloud environment. >>>>> >>>>> Replacing this feature instead of creating a new option is not a good >>>>> idea indeed. I missed something ? >>>>> >>>>> Thanks, Anand >>>>> >>>>>> +Also, if destination file/block device does not exist, >>>>>> *--rootdir* will not >>>>>> +create the image file, to make it follow the normal mkfs behavior. >>>> >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe >>>> linux-btrfs" in >>>> the body of a message to majordomo@vger.kernel.org >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: > On 2017-09-24 10:08, Goffredo Baroncelli wrote: > > On 09/24/2017 12:10 PM, Anand Jain wrote: A lot of points in this thread, let me address them here. I don't want to remove --rootdir functionality, the fix that's being proposed removes the minimalization -- feature that was not well known, but I understand it's useful (and already used). I'd like to fix that in another way, eg. as an option to mkfs or a separate tool. I'm not worried about adding more code or code complexity. If we do it right it's not a problem in the long run. But people for some reason like to delete other people's code or functionality. Regarding guessing number of users, this is always hard. So if there's one vocal enough to let us know about the usecase, it's IMHO good time to explore the it, code-wise and documentation-wise, and fix it or improve. So, what next. I'd like to get rid of the custom chunk allocator, namely because of the known 1MB area misuse and duplication. Implementing the minimalization might need some preparatory work and I don't have a realistic ETA now. Ideally we'd fix both problems in one version, as I'd rather avoid "temporary" solution to drop the minimalization with the promise to put it back later. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017年09月28日 00:20, David Sterba wrote: > On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: >> On 2017-09-24 10:08, Goffredo Baroncelli wrote: >>> On 09/24/2017 12:10 PM, Anand Jain wrote: > > A lot of points in this thread, let me address them here. > > I don't want to remove --rootdir functionality, the fix that's being > proposed removes the minimalization -- feature that was not well known, > but I understand it's useful (and already used). > > I'd like to fix that in another way, eg. as an option to mkfs or a > separate tool. > > I'm not worried about adding more code or code complexity. If we do it > right it's not a problem in the long run. But people for some reason > like to delete other people's code or functionality. > > Regarding guessing number of users, this is always hard. So if there's > one vocal enough to let us know about the usecase, it's IMHO good time > to explore the it, code-wise and documentation-wise, and fix it or > improve. > > So, what next. I'd like to get rid of the custom chunk allocator, namely > because of the known 1MB area misuse and duplication. > > Implementing the minimalization might need some preparatory work and I > don't have a realistic ETA now. Well, if using over-reserve-then-shrink method, it could be done, without much hassle. However ETA maybe delayed to middle of Oct, as I'm going to enjoy my holiday during 1st Oct to 7th Oct. Thanks, Qu > Ideally we'd fix both problems in one > version, as I'd rather avoid "temporary" solution to drop the > minimalization with the promise to put it back later. > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017-09-27 20:00, Qu Wenruo wrote: > > > On 2017年09月28日 00:20, David Sterba wrote: >> On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: >>> On 2017-09-24 10:08, Goffredo Baroncelli wrote: >>>> On 09/24/2017 12:10 PM, Anand Jain wrote: >> >> A lot of points in this thread, let me address them here. >> >> I don't want to remove --rootdir functionality, the fix that's being >> proposed removes the minimalization -- feature that was not well known, >> but I understand it's useful (and already used). >> >> I'd like to fix that in another way, eg. as an option to mkfs or a >> separate tool. >> >> I'm not worried about adding more code or code complexity. If we do it >> right it's not a problem in the long run. But people for some reason >> like to delete other people's code or functionality. >> >> Regarding guessing number of users, this is always hard. So if there's >> one vocal enough to let us know about the usecase, it's IMHO good time >> to explore the it, code-wise and documentation-wise, and fix it or >> improve. >> >> So, what next. I'd like to get rid of the custom chunk allocator, namely >> because of the known 1MB area misuse and duplication. >> >> Implementing the minimalization might need some preparatory work and I >> don't have a realistic ETA now. > > Well, if using over-reserve-then-shrink method, it could be done, > without much hassle. It _should_ be possible to compute the exact size required though. As outlined in one of my other replies, an absolute minimal filesystem should in theory consist of the following space usage: 1. 1MB (for the reserved space at the beginning). 2. However many superblocks it should have given the size. 3. The total amount of file data and extended attribute data to be included, rounding up for block size 4. The exact amount of metadata space needed to represent the tree from 3, also rounding up for block size. 5. The exact amount of system chunk space needed to handle 3 and 4, plus enough room to allocate at least one more chunk of each type (to ultimately allow for resizing the filesystem if desired). 6. Exactly enough reserved metadata space to resize the FS (alternatively, the standard space for the GlobalReserve, which should be enough and then some). Computing this is non-trivial for a human, and even with a computer requires knowledge of how the chunk allocator is implemented. mkfs should have that knowledge though, so in theory it is reasonably well positioned to just compute this, allocate that much space, and then generate the filesystem. The complaints I have about trying to do this manually in two passes are that: 1. Computing the above by hand is not easy. 2. Computing it by hand and then running mkfs on the resultant file doesn't work most of the time. As a result, I would think this could easily be handled in the following steps: 1. Scan the contents of the --rootdir option to determine total size needed. 2. Compute the required allocation and allocate it. 3. Generate the filesystem image. This has an inherent TOCTOU race, but it's one that a lot of archiving tools (tar being a prime example) already have, and it's not likely that people will hit it since you're not likely to be using a changing directory for --rootdir. > > However ETA maybe delayed to middle of Oct, as I'm going to enjoy my > holiday during 1st Oct to 7th Oct. Entirely understandable, enjoy your time off! -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 09/28/2017 02:00 AM, Qu Wenruo wrote: > > > On 2017年09月28日 00:20, David Sterba wrote: >> On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: >>> On 2017-09-24 10:08, Goffredo Baroncelli wrote: >>>> On 09/24/2017 12:10 PM, Anand Jain wrote: >> >> A lot of points in this thread, let me address them here. >> >> I don't want to remove --rootdir functionality, the fix that's being >> proposed removes the minimalization -- feature that was not well known, >> but I understand it's useful (and already used). >> >> I'd like to fix that in another way, eg. as an option to mkfs or a >> separate tool. >> >> I'm not worried about adding more code or code complexity. If we do it >> right it's not a problem in the long run. But people for some reason >> like to delete other people's code or functionality. >> >> Regarding guessing number of users, this is always hard. So if there's >> one vocal enough to let us know about the usecase, it's IMHO good time >> to explore the it, code-wise and documentation-wise, and fix it or >> improve. >> >> So, what next. I'd like to get rid of the custom chunk allocator, namely >> because of the known 1MB area misuse and duplication. >> >> Implementing the minimalization might need some preparatory work and I >> don't have a realistic ETA now. > > Well, if using over-reserve-then-shrink method, it could be done, without much hassle. What about doing it on a file instead of a device ? As sparse file, it would be less expensive to enlarge then shrink. I think that who need to build a filesystem with "shrink", doesn't need to create it on a real block device > > However ETA maybe delayed to middle of Oct, as I'm going to enjoy my holiday during 1st Oct to 7th Oct. > > Thanks, > Qu > >> Ideally we'd fix both problems in one >> version, as I'd rather avoid "temporary" solution to drop the >> minimalization with the promise to put it back later. >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
On 2017年09月30日 00:57, Goffredo Baroncelli wrote: > On 09/28/2017 02:00 AM, Qu Wenruo wrote: >> >> >> On 2017年09月28日 00:20, David Sterba wrote: >>> On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: >>>> On 2017-09-24 10:08, Goffredo Baroncelli wrote: >>>>> On 09/24/2017 12:10 PM, Anand Jain wrote: >>> >>> A lot of points in this thread, let me address them here. >>> >>> I don't want to remove --rootdir functionality, the fix that's being >>> proposed removes the minimalization -- feature that was not well known, >>> but I understand it's useful (and already used). >>> >>> I'd like to fix that in another way, eg. as an option to mkfs or a >>> separate tool. >>> >>> I'm not worried about adding more code or code complexity. If we do it >>> right it's not a problem in the long run. But people for some reason >>> like to delete other people's code or functionality. >>> >>> Regarding guessing number of users, this is always hard. So if there's >>> one vocal enough to let us know about the usecase, it's IMHO good time >>> to explore the it, code-wise and documentation-wise, and fix it or >>> improve. >>> >>> So, what next. I'd like to get rid of the custom chunk allocator, namely >>> because of the known 1MB area misuse and duplication. >>> >>> Implementing the minimalization might need some preparatory work and I >>> don't have a realistic ETA now. >> >> Well, if using over-reserve-then-shrink method, it could be done, without much hassle. > > What about doing it on a file instead of a device ? As sparse file, it would be less expensive to enlarge then shrink. I think that who need to build a filesystem with "shrink", doesn't need to create it on a real block device For device, nothing different, just v3 patchset will handle it. For file, sparse file of course. Thanks, Qu >> >> However ETA maybe delayed to middle of Oct, as I'm going to enjoy my holiday during 1st Oct to 7th Oct. >> >> Thanks, >> Qu >> >>> Ideally we'd fix both problems in one >>> version, as I'd rather avoid "temporary" solution to drop the >>> minimalization with the promise to put it back later. >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017-09-29 23:33, Qu Wenruo wrote: > > > On 2017年09月30日 00:57, Goffredo Baroncelli wrote: >> On 09/28/2017 02:00 AM, Qu Wenruo wrote: >>> >>> >>> On 2017年09月28日 00:20, David Sterba wrote: >>>> On Mon, Sep 25, 2017 at 07:15:30AM -0400, Austin S. Hemmelgarn wrote: >>>>> On 2017-09-24 10:08, Goffredo Baroncelli wrote: >>>>>> On 09/24/2017 12:10 PM, Anand Jain wrote: >>>> >>>> A lot of points in this thread, let me address them here. >>>> >>>> I don't want to remove --rootdir functionality, the fix that's being >>>> proposed removes the minimalization -- feature that was not well known, >>>> but I understand it's useful (and already used). >>>> >>>> I'd like to fix that in another way, eg. as an option to mkfs or a >>>> separate tool. >>>> >>>> I'm not worried about adding more code or code complexity. If we do it >>>> right it's not a problem in the long run. But people for some reason >>>> like to delete other people's code or functionality. >>>> >>>> Regarding guessing number of users, this is always hard. So if there's >>>> one vocal enough to let us know about the usecase, it's IMHO good time >>>> to explore the it, code-wise and documentation-wise, and fix it or >>>> improve. >>>> >>>> So, what next. I'd like to get rid of the custom chunk allocator, >>>> namely >>>> because of the known 1MB area misuse and duplication. >>>> >>>> Implementing the minimalization might need some preparatory work and I >>>> don't have a realistic ETA now. >>> >>> Well, if using over-reserve-then-shrink method, it could be done, >>> without much hassle. >> >> What about doing it on a file instead of a device ? As sparse file, it >> would be less expensive to enlarge then shrink. I think that who need >> to build a filesystem with "shrink", doesn't need to create it on a >> real block device > > For device, nothing different, just v3 patchset will handle it. Agreed on this point. > > For file, sparse file of course. But not on this one. Unless the image gets properly compacted, a sparse file will only help when you're just storing the image on a filesystem. It doesn't really help at all for when you need to put it on a physical device afterwards (except possibly if you're using thin provisioning). The reason I (at least) am complaining about losing this feature isn't about having space efficiency when storing image files on a filesystem, it's about time efficiency in transferring the image either to a device after generation (if you're going to multiple devices, it makes more sense to just generate an image file instead of writing directly to the first device in most cases), or to another system where it will ultimately be written to a device. As a more specific example, look at how installation of Linux (preferably Raspbian) is typically done on a Raspberry Pi. You have a base SD-card image that is designed to fit on a 1G SD card, and the root filesystem then gets resized automatically on first boot to fill the card. You still need to copy that whole 1G of data to a _slow_ SD card before you can do anything with it, because you can't assume the card is empty and do sparse writes (and very few tools used for writing out disk images can do sparse writes). You also have to copy all that data to download the image, and while they're distributed compressed, compressing runs of empty space still takes space. If that instead used image generation similar to the current behavior of the --rootdir option, a reasonable amount of time would be saved in most steps, simply because the image was smaller (the 1G image has 300MB or more of empty space in it). As another example, when dealing with seed devices, it makes just as much if not more sense if you're using LVM to store the data to create an LV that is exactly as large as needed for the seed device, and no bigger. Using sparse files similarly doesn't work for that unless you're using thin provisioning and don't mind LVM complaining all the time about over-provisioning your space. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 10/02/2017 01:47 PM, Austin S. Hemmelgarn wrote: >>> >>> What about doing it on a file instead of a device ? As sparse file, it would be less expensive to enlarge then shrink. I think that who need to build a filesystem with "shrink", doesn't need to create it on a real block device >> >> For device, nothing different, just v3 patchset will handle it. > Agreed on this point. >> >> For file, sparse file of course. > But not on this one. Unless the image gets properly compacted, a sparse file will only help when you're just storing the image on a filesystem. I think that you have misunderstood my proposal... My suggestion is to create the image using a file, and after image creation compact it, and then cut it at the end. So you don't have to care about the space needing during the process (before the shrinking). Today mkfs.btrfs fails to create an image on an empty file ghigo@venice:/tmp$ mkdir test ghigo@venice:/tmp$ mkdir test/test1 ghigo@venice:/tmp$ touch test/test1/file ghigo@venice:/tmp$ mkfs.btrfs --root test disk.img btrfs-progs v4.12 See http://btrfs.wiki.kernel.org for more information. ERROR: failed to check size for disk.img: No such file or directory ghigo@venice:/tmp$ touch disk.img ghigo@venice:/tmp$ mkfs.btrfs --root test disk.img btrfs-progs v4.12 See http://btrfs.wiki.kernel.org for more information. ERROR: 'disk.img' is too small to make a usable filesystem ERROR: minimum size for each btrfs device is 41943040 you have to create a big enough ghigo@venice:/tmp$ truncate -s 10G disk.img ghigo@venice:/tmp$ mkfs.btrfs --root test disk.img btrfs-progs v4.12 See http://btrfs.wiki.kernel.org for more information. [...] BR
diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc index d53d9e26..645a2881 100644 --- a/Documentation/mkfs.btrfs.asciidoc +++ b/Documentation/mkfs.btrfs.asciidoc @@ -106,6 +106,19 @@ Please see the mount option 'discard' for that in `btrfs`(5). *-r|--rootdir <rootdir>*:: Populate the toplevel subvolume with files from 'rootdir'. This does not require root permissions and does not mount the filesystem. ++ +With this option, only one device can be specified. ++ +NOTE: User should make sure the block device/file has large enough space to +contain the source directory and has enough previllege to read source directory. +Or mkfs will just fail. ++ +WARNING: Before v4.14 btrfs-progs, *--rootdir* will shrink the filesystem, +prevent user to make use of the remaining space. +In v4.14 btrfs-progs, this behavior is changed, and will not shrink the fs. +The result should be the same as `mkfs`, `mount` and then `cp -r`. + +Also, if destination file/block device does not exist, *--rootdir* will not +create the image file, to make it follow the normal mkfs behavior. *-O|--features <feature1>[,<feature2>...]*:: A list of filesystem features turned on at mkfs time. Not all features are
Add extra limitation explained for --rootdir option, including: 1) Size limitation Now I decide to follow "mkfs.ext4 -d" behavior, so user is responsible to make sure the block device/file is large enough. 2) Read permission If user can't read the content, mkfs will just fail. So user is also responsible to make sure to have enough privilege. 3) Extra warning about the behavior change Since we we don't shrink fs the create file image, add such warning in documentation. Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com> --- Documentation/mkfs.btrfs.asciidoc | 13 +++++++++++++ 1 file changed, 13 insertions(+)