[RFC,2/3] btrfs-progs: kernel based default features for mkfs
diff mbox

Message ID 1445417149-804-2-git-send-email-anand.jain@oracle.com
State New
Headers show

Commit Message

Anand Jain Oct. 21, 2015, 8:45 a.m. UTC
mkfs from latest btrfs-progs will enable latest default features,
and if the kernel is down-rev and does not support a latest default
feature then mount fails, as expected.

This patch disables default features based on the running kernel.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 mkfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Qu Wenruo Oct. 21, 2015, 9:12 a.m. UTC | #1
Anand Jain wrote on 2015/10/21 16:45 +0800:
> mkfs from latest btrfs-progs will enable latest default features,
> and if the kernel is down-rev and does not support a latest default
> feature then mount fails, as expected.
>
> This patch disables default features based on the running kernel.
>
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>   mkfs.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mkfs.c b/mkfs.c
> index a5802f7..2b9d734 100644
> --- a/mkfs.c
> +++ b/mkfs.c
> @@ -1357,10 +1357,13 @@ int main(int ac, char **av)
>   	int dev_cnt = 0;
>   	int saved_optind;
>   	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
> -	u64 features = BTRFS_MKFS_DEFAULT_FEATURES;
> +	u64 features;
>   	struct mkfs_allocation allocation = { 0 };
>   	struct btrfs_mkfs_config mkfs_cfg;
>
> +	features = btrfs_features_allowed_by_kernel();
> +	features &= BTRFS_MKFS_DEFAULT_FEATURES;
> +

Despite the problem of btrfs_features_allowed_by_kernel() I mentioned in 
previous mail,
the behavior is a little aggressive for me.

So a user with old kernel won't be able to create a filesystem with 
newer feature forever.
Maybe the user are just making btrfs for his or her newer kernel?

IMHO, it's better to output a warning other than just change features 
without any information.

Thanks,
Qu

>   	while(1) {
>   		int c;
>   		static const struct option long_options[] = {
>
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Anand Jain Oct. 21, 2015, 2:15 p.m. UTC | #2
Thanks for the comments.. more below.

On 10/21/2015 05:12 PM, Qu Wenruo wrote:
>
>
> Anand Jain wrote on 2015/10/21 16:45 +0800:
>> mkfs from latest btrfs-progs will enable latest default features,
>> and if the kernel is down-rev and does not support a latest default
>> feature then mount fails, as expected.
>>
>> This patch disables default features based on the running kernel.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   mkfs.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mkfs.c b/mkfs.c
>> index a5802f7..2b9d734 100644
>> --- a/mkfs.c
>> +++ b/mkfs.c
>> @@ -1357,10 +1357,13 @@ int main(int ac, char **av)
>>       int dev_cnt = 0;
>>       int saved_optind;
>>       char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
>> -    u64 features = BTRFS_MKFS_DEFAULT_FEATURES;
>> +    u64 features;
>>       struct mkfs_allocation allocation = { 0 };
>>       struct btrfs_mkfs_config mkfs_cfg;
>>
>> +    features = btrfs_features_allowed_by_kernel();
>> +    features &= BTRFS_MKFS_DEFAULT_FEATURES;
>> +
>
> Despite the problem of btrfs_features_allowed_by_kernel() I mentioned in
> previous mail,
> the behavior is a little aggressive for me.
>
> So a user with old kernel won't be able to create a filesystem with
> newer feature forever.
> Maybe the user are just making btrfs for his or her newer kernel?

   I am not understanding the complete picture here, is there any 
example that you can quote. ?

Thanks, Anand

> IMHO, it's better to output a warning other than just change features
> without any information.
>
> Thanks,
> Qu
>
>>       while(1) {
>>           int c;
>>           static const struct option long_options[] = {
>>
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Qu Wenruo Oct. 21, 2015, 2:25 p.m. UTC | #3
? 2015?10?21? 22:15, Anand Jain ??:
>
> Thanks for the comments.. more below.
>
> On 10/21/2015 05:12 PM, Qu Wenruo wrote:
>>
>>
>> Anand Jain wrote on 2015/10/21 16:45 +0800:
>>> mkfs from latest btrfs-progs will enable latest default features,
>>> and if the kernel is down-rev and does not support a latest default
>>> feature then mount fails, as expected.
>>>
>>> This patch disables default features based on the running kernel.
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>   mkfs.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mkfs.c b/mkfs.c
>>> index a5802f7..2b9d734 100644
>>> --- a/mkfs.c
>>> +++ b/mkfs.c
>>> @@ -1357,10 +1357,13 @@ int main(int ac, char **av)
>>>       int dev_cnt = 0;
>>>       int saved_optind;
>>>       char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
>>> -    u64 features = BTRFS_MKFS_DEFAULT_FEATURES;
>>> +    u64 features;
>>>       struct mkfs_allocation allocation = { 0 };
>>>       struct btrfs_mkfs_config mkfs_cfg;
>>>
>>> +    features = btrfs_features_allowed_by_kernel();
>>> +    features &= BTRFS_MKFS_DEFAULT_FEATURES;
>>> +
>>
>> Despite the problem of btrfs_features_allowed_by_kernel() I mentioned in
>> previous mail,
>> the behavior is a little aggressive for me.
>>
>> So a user with old kernel won't be able to create a filesystem with
>> newer feature forever.
>> Maybe the user are just making btrfs for his or her newer kernel?
>
>    I am not understanding the complete picture here, is there any
> example that you can quote. ?
>
> Thanks, Anand
>

Sorry my fault.
Your features are set before parse_fs_features()

So it's just my misunderstanding.

However, I still prefer warning other than just changing default features.

Thanks,
Qu

>> IMHO, it's better to output a warning other than just change features
>> without any information.
>>
>> Thanks,
>> Qu
>>
>>>       while(1) {
>>>           int c;
>>>           static const struct option long_options[] = {
>>>
>> --
>> 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
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Anand Jain Oct. 22, 2015, 3:09 a.m. UTC | #4
Hi,

  more details about this RFC as below..


> So a user with old kernel won't be able to create a filesystem with
> newer feature forever.

  Thats not true. Here below is an example of the problem and fix
  in action.

> Maybe the user are just making btrfs for his or her newer kernel?

  Yes. Thats still possible as below.



[[current problem]]

I am on 3.8 kernel which does not support the skinny-metadata feature.
---------
# uname -r
3.8.13-98.4.1.el6uek.x86_64
-------------

Lets say customer upgraded the latest btrfs-progs as they wanted better
cli interface, reporting and document which is only available in the
latest btrfs-progs.

As btrfs-progs is backward kernel compatible, they don't have to
upgrade the kernel.

But as skinny-metadata is part of the "mkfs default feature", thats get
enabled by default during mkfs.

----------
# mkfs.btrfs -f /dev/sdc
btrfs-progs v4.2.2-7-g03cf344
See http://btrfs.wiki.kernel.org for more information.

Label:              (null)
UUID:               bb85b156-35eb-49a5-be5a-512fec1abab4
Node size:          16384
Sector size:        4096
Filesystem size:    3.00GiB
Block group profiles:
   Data:             single            8.00MiB
   Metadata:         DUP             161.56MiB
   System:           DUP              12.00MiB
SSD detected:       no
Incompat features:  extref, skinny-metadata         <-----
Number of devices:  1
Devices:
    ID        SIZE  PATH
     1     3.00GiB  /dev/sdc
-------------------

mount on the running kernel 3.8 fails, as there is no kernel support
for skinny-metadata
-----------
# mount /dev/sdc /btrfs
mount: wrong fs type, bad option, bad superblock on /dev/sdc,
        missing codepage or helper program, or other error
        In some cases useful info is found in syslog - try
        dmesg | tail  or so

BTRFS: couldn't mount because of unsupported optional features (100).
btrfs: open_ctree failed
----------

Customers need to upgrade the kernel also to mount this FS.


[[current solution]]

User must know that their running kernel does not support
skinny metadata and disable features accordingly as below.

------------
# mkfs.btrfs -f -O ^skinny-metadata /dev/sdc > /dev/null && mount 
/dev/sdc /btrfs
# echo $?
0
------------


[[problem with the current solution]]

btrfs-progs is backward kernel compatible.

But the default feature as set during mkfs is very btrfs-progs centric,
and is not in sync with the current running kernel.


[[new proposed, with the patch]]

- the default-features that are not supported by the running kernel
  are masked.

  So now the default mkfs.btrfs and mount works. As progs finds that
  kernel version is too old to support skinny-metadata and remotes is
  from the default feature list.

-------------------
# uname -r
3.8.13-98.4.1.el6uek.x86_64


# mkfs.btrfs -f /dev/sdc
btrfs-progs v4.2.2-7-g03cf344
See http://btrfs.wiki.kernel.org for more information.

Label:              (null)
UUID:               f2513ff0-6d94-4b6a-8bbf-ff53d343fa62
Node size:          16384
Sector size:        4096
Filesystem size:    3.00GiB
Block group profiles:
   Data:             single            8.00MiB
   Metadata:         DUP             161.56MiB
   System:           DUP              12.00MiB
SSD detected:       no
Incompat features:  extref  <-----
Number of devices:  1
Devices:
    ID        SIZE  PATH
     1     3.00GiB  /dev/sdc

# mount /dev/sdc /btrfs
-------------------


However as Qu pointed out if user wants to create FS with a feature that
is not supported by running kernel. They still have the choice to enable
it using -O option. as below. however they won't be able to mount it
unless kernel is upgraded as well.

-------
# mkfs.btrfs -f -O skinny-metadata /dev/sdc
btrfs-progs v4.2.2-7-g03cf344
See http://btrfs.wiki.kernel.org for more information.

Label:              (null)
UUID:               30c018ab-3d2a-4acc-8287-3f28c5324fca
Node size:          16384
Sector size:        4096
Filesystem size:    3.00GiB
Block group profiles:
   Data:             single            8.00MiB
   Metadata:         DUP             161.56MiB
   System:           DUP              12.00MiB
SSD detected:       no
Incompat features:  extref, skinny-metadata   <----
Number of devices:  1
Devices:
    ID        SIZE  PATH
     1     3.00GiB  /dev/sdc

# mount /dev/sdc /btrfs
mount: wrong fs type, bad option, bad superblock on /dev/sdc,
        missing codepage or helper program, or other error
        In some cases useful info is found in syslog - try
        dmesg | tail  or so
#
---------

In nut shell this patch makes _mkfs and btrfs-convert default features_
dynamically aligned with the running kernel.

Thanks, Anand
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Qu Wenruo Oct. 22, 2015, 4:10 a.m. UTC | #5
Anand Jain wrote on 2015/10/22 11:09 +0800:
>
> Hi,
>
>   more details about this RFC as below..
>
>
>> So a user with old kernel won't be able to create a filesystem with
>> newer feature forever.
>
>   Thats not true. Here below is an example of the problem and fix
>   in action.
>
>> Maybe the user are just making btrfs for his or her newer kernel?
>
>   Yes. Thats still possible as below.
>
>
>
> [[current problem]]
>
> I am on 3.8 kernel which does not support the skinny-metadata feature.
> ---------
> # uname -r
> 3.8.13-98.4.1.el6uek.x86_64
> -------------
>
> Lets say customer upgraded the latest btrfs-progs as they wanted better
> cli interface, reporting and document which is only available in the
> latest btrfs-progs.
>
> As btrfs-progs is backward kernel compatible, they don't have to
> upgrade the kernel.
>
> But as skinny-metadata is part of the "mkfs default feature", thats get
> enabled by default during mkfs.

For real customer case, that's really a problem.
Customer is god, right?

But on the other hand, normally support team only provides support for 
their own product.
Here "product" may be their distribution or other software, but never 
any software customer build from source by themselves.

If customer want to upgrade btrfs-progs, they should use the repo from 
distribution, not compile by themselves.

And it will be the responsibility of backport team to backport needed 
features for kernel/btrfs-progs or change default features.

But unfortunately(or fortunately?), we are not backport team.

>
> ----------
> # mkfs.btrfs -f /dev/sdc
> btrfs-progs v4.2.2-7-g03cf344
> See http://btrfs.wiki.kernel.org for more information.
>
> Label:              (null)
> UUID:               bb85b156-35eb-49a5-be5a-512fec1abab4
> Node size:          16384
> Sector size:        4096
> Filesystem size:    3.00GiB
> Block group profiles:
>    Data:             single            8.00MiB
>    Metadata:         DUP             161.56MiB
>    System:           DUP              12.00MiB
> SSD detected:       no
> Incompat features:  extref, skinny-metadata         <-----
> Number of devices:  1
> Devices:
>     ID        SIZE  PATH
>      1     3.00GiB  /dev/sdc
> -------------------
>
> mount on the running kernel 3.8 fails, as there is no kernel support
> for skinny-metadata
> -----------
> # mount /dev/sdc /btrfs
> mount: wrong fs type, bad option, bad superblock on /dev/sdc,
>         missing codepage or helper program, or other error
>         In some cases useful info is found in syslog - try
>         dmesg | tail  or so
>
> BTRFS: couldn't mount because of unsupported optional features (100).
> btrfs: open_ctree failed
> ----------
>
> Customers need to upgrade the kernel also to mount this FS.
>
>
> [[current solution]]
>
> User must know that their running kernel does not support
> skinny metadata and disable features accordingly as below.
>
> ------------
> # mkfs.btrfs -f -O ^skinny-metadata /dev/sdc > /dev/null && mount
> /dev/sdc /btrfs
> # echo $?
> 0
> ------------
>
>
> [[problem with the current solution]]
>
> btrfs-progs is backward kernel compatible.
>
> But the default feature as set during mkfs is very btrfs-progs centric,
> and is not in sync with the current running kernel.
>
>
> [[new proposed, with the patch]]
>
> - the default-features that are not supported by the running kernel
>   are masked.
>
>   So now the default mkfs.btrfs and mount works. As progs finds that
>   kernel version is too old to support skinny-metadata and remotes is
>   from the default feature list.
>
> -------------------
> # uname -r
> 3.8.13-98.4.1.el6uek.x86_64
>
>
> # mkfs.btrfs -f /dev/sdc
> btrfs-progs v4.2.2-7-g03cf344
> See http://btrfs.wiki.kernel.org for more information.
>
> Label:              (null)
> UUID:               f2513ff0-6d94-4b6a-8bbf-ff53d343fa62
> Node size:          16384
> Sector size:        4096
> Filesystem size:    3.00GiB
> Block group profiles:
>    Data:             single            8.00MiB
>    Metadata:         DUP             161.56MiB
>    System:           DUP              12.00MiB
> SSD detected:       no
> Incompat features:  extref  <-----
> Number of devices:  1
> Devices:
>     ID        SIZE  PATH
>      1     3.00GiB  /dev/sdc
>
> # mount /dev/sdc /btrfs
> -------------------
>
>
> However as Qu pointed out if user wants to create FS with a feature that
> is not supported by running kernel. They still have the choice to enable
> it using -O option. as below. however they won't be able to mount it
> unless kernel is upgraded as well.
>
> -------
> # mkfs.btrfs -f -O skinny-metadata /dev/sdc
> btrfs-progs v4.2.2-7-g03cf344
> See http://btrfs.wiki.kernel.org for more information.
>
> Label:              (null)
> UUID:               30c018ab-3d2a-4acc-8287-3f28c5324fca
> Node size:          16384
> Sector size:        4096
> Filesystem size:    3.00GiB
> Block group profiles:
>    Data:             single            8.00MiB
>    Metadata:         DUP             161.56MiB
>    System:           DUP              12.00MiB
> SSD detected:       no
> Incompat features:  extref, skinny-metadata   <----
> Number of devices:  1
> Devices:
>     ID        SIZE  PATH
>      1     3.00GiB  /dev/sdc
>
> # mount /dev/sdc /btrfs
> mount: wrong fs type, bad option, bad superblock on /dev/sdc,
>         missing codepage or helper program, or other error
>         In some cases useful info is found in syslog - try
>         dmesg | tail  or so
> #
> ---------
>
> In nut shell this patch makes _mkfs and btrfs-convert default features_
> dynamically aligned with the running kernel.

Maybe just personal choice, I still prefer not to change default 
features, output warning should be good enough for such case,
due to the unreliableness of version check.

Thanks,
Qu

>
> Thanks, Anand
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Jeff Mahoney Oct. 23, 2015, 3:24 p.m. UTC | #6
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 10/21/15 4:45 AM, Anand Jain wrote:
> mkfs from latest btrfs-progs will enable latest default features, 
> and if the kernel is down-rev and does not support a latest
> default feature then mount fails, as expected.
> 
> This patch disables default features based on the running kernel.

I like the idea generally based on comments further in the thread, but
what I don't like is:

1) It's silent.
2) There's no way to override it.

If we're going to change the defaults at runtime, we should tell the
user what has changed and why.  Otherwise, an identical mkfs.btrfs
binary will behave differently on different systems without feedback
and that violates the principle of least surprise.  If they want to do
what Qu suggests later in the thread, where the device is being
prepared for use on a newer kernel, it should be possible to force it.
 The normal -f should be fine there.

- -Jeff

> Signed-off-by: Anand Jain <anand.jain@oracle.com> --- mkfs.c | 5
> ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mkfs.c b/mkfs.c index a5802f7..2b9d734 100644 ---
> a/mkfs.c +++ b/mkfs.c @@ -1357,10 +1357,13 @@ int main(int ac, char
> **av) int dev_cnt = 0; int saved_optind; char
> fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 }; -	u64 features =
> BTRFS_MKFS_DEFAULT_FEATURES; +	u64 features; struct mkfs_allocation
> allocation = { 0 }; struct btrfs_mkfs_config mkfs_cfg;
> 
> +	features = btrfs_features_allowed_by_kernel(); +	features &=
> BTRFS_MKFS_DEFAULT_FEATURES; + while(1) { int c; static const
> struct option long_options[] = {
> 


- -- 
Jeff Mahoney
SUSE Labs
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Anand Jain Oct. 26, 2015, 11:42 a.m. UTC | #7
Thanks Jeff for the comments.

On 10/23/2015 11:24 PM, Jeff Mahoney wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 10/21/15 4:45 AM, Anand Jain wrote:
>> mkfs from latest btrfs-progs will enable latest default features,
>> and if the kernel is down-rev and does not support a latest
>> default feature then mount fails, as expected.
>>
>> This patch disables default features based on the running kernel.
>
> I like the idea generally based on comments further in the thread, but
> what I don't like is:
>
> 1) It's silent.

  Will add warning.

> 2) There's no way to override it.

> If we're going to change the defaults at runtime, we should tell the
> user what has changed and why.  Otherwise, an identical mkfs.btrfs
> binary will behave differently on different systems without feedback
> and that violates the principle of least surprise.  If they want to do
> what Qu suggests later in the thread, where the device is being
> prepared for use on a newer kernel, it should be possible to force it.
>   The normal -f should be fine there.

  Sill have no idea how to get this, trying.

Thanks, Anand


> - -Jeff
>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com> --- mkfs.c | 5
>> ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mkfs.c b/mkfs.c index a5802f7..2b9d734 100644 ---
>> a/mkfs.c +++ b/mkfs.c @@ -1357,10 +1357,13 @@ int main(int ac, char
>> **av) int dev_cnt = 0; int saved_optind; char
>> fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 }; -	u64 features =
>> BTRFS_MKFS_DEFAULT_FEATURES; +	u64 features; struct mkfs_allocation
>> allocation = { 0 }; struct btrfs_mkfs_config mkfs_cfg;
>>
>> +	features = btrfs_features_allowed_by_kernel(); +	features &=
>> BTRFS_MKFS_DEFAULT_FEATURES; + while(1) { int c; static const
>> struct option long_options[] = {
>>
>
>
> - --
> Jeff Mahoney
> SUSE Labs
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Patch
diff mbox

diff --git a/mkfs.c b/mkfs.c
index a5802f7..2b9d734 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -1357,10 +1357,13 @@  int main(int ac, char **av)
 	int dev_cnt = 0;
 	int saved_optind;
 	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
-	u64 features = BTRFS_MKFS_DEFAULT_FEATURES;
+	u64 features;
 	struct mkfs_allocation allocation = { 0 };
 	struct btrfs_mkfs_config mkfs_cfg;
 
+	features = btrfs_features_allowed_by_kernel();
+	features &= BTRFS_MKFS_DEFAULT_FEATURES;
+
 	while(1) {
 		int c;
 		static const struct option long_options[] = {