| Message ID | 20160712003537.GA27653@vader.dhcp.thefacebook.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > Hey, Darrick, > > generic/182 is failing on Btrfs for me with the following output: > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > @@ -1,12 +1,10 @@ > QA output created by 182 > Create the original files > -dedupe: Extents did not match. > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > Compare against check files > Make the original file almost dedup-able > -dedupe: Extents did not match. > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > It looks like that test is checking that a dedupe with length == 0 is > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > can tell, it never did, but maybe I'm just confused. What was the > behavior when you introduced that test? That seems like a reasonable > thing to do, but I wanted to clear this up before changing/fixing Btrfs. It's a shortcut that we're introducing in the upcoming XFS implementation, since it shares the same back end as clone/clonerange, which both have this behavior. --D > > Thanks. > > 1: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/ioctl.c?h=v4.7-rc7#n3122 > -- > Omar -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > > Hey, Darrick, > > > > generic/182 is failing on Btrfs for me with the following output: > > > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > > @@ -1,12 +1,10 @@ > > QA output created by 182 > > Create the original files > > -dedupe: Extents did not match. > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > > Compare against check files > > Make the original file almost dedup-able > > -dedupe: Extents did not match. > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > > > It looks like that test is checking that a dedupe with length == 0 is > > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > > can tell, it never did, but maybe I'm just confused. What was the > > behavior when you introduced that test? That seems like a reasonable > > thing to do, but I wanted to clear this up before changing/fixing Btrfs. > > It's a shortcut that we're introducing in the upcoming XFS implementation, > since it shares the same back end as clone/clonerange, which both have > this behavior. The support for zero length does not seem to be mentioned anywhere with the dedupe range ioctl [1], so the current implemetnation is "up to spec". That it should be valid is hidden in clone_verify_area where a zero length is substituted with OFFSET_MAX http://lxr.free-electrons.com/source/fs/read_write.c#L1607 So it looks like it's up to the implementation in the filesystem to handle that. As the btrfs ioctl was extent-based, a zero length extent does not make sense, so this case was not handled. But in your patch 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 btrfs: use new dedupe data function pointer it was suddenly expected to work. So the missing bits are either 'not supported' for zero length or actually implement iteration over the whole file. [1] https://www.mankier.com/2/ioctl_fideduperange -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > It's a shortcut that we're introducing in the upcoming XFS implementation, > since it shares the same back end as clone/clonerange, which both have > this behavior. We will have to preserve the existing btrfs semantics when reusing the ioctl number. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Jul 13, 2016 at 03:19:38PM +0200, David Sterba wrote: > On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > > On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > > > Hey, Darrick, > > > > > > generic/182 is failing on Btrfs for me with the following output: > > > > > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > > > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > > > @@ -1,12 +1,10 @@ > > > QA output created by 182 > > > Create the original files > > > -dedupe: Extents did not match. > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > > > Compare against check files > > > Make the original file almost dedup-able > > > -dedupe: Extents did not match. > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > > > > > It looks like that test is checking that a dedupe with length == 0 is > > > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > > > can tell, it never did, but maybe I'm just confused. What was the > > > behavior when you introduced that test? That seems like a reasonable > > > thing to do, but I wanted to clear this up before changing/fixing Btrfs. > > > > It's a shortcut that we're introducing in the upcoming XFS implementation, > > since it shares the same back end as clone/clonerange, which both have > > this behavior. > > The support for zero length does not seem to be mentioned anywhere with > the dedupe range ioctl [1], so the current implemetnation is "up to > spec". That it should be valid is hidden in clone_verify_area where a > zero length is substituted with OFFSET_MAX > > http://lxr.free-electrons.com/source/fs/read_write.c#L1607 > > So it looks like it's up to the implementation in the filesystem to > handle that. As the btrfs ioctl was extent-based, a zero length extent > does not make sense, so this case was not handled. But in your patch > > 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 > btrfs: use new dedupe data function pointer > > it was suddenly expected to work. So the missing bits are either 'not > supported' for zero length or actually implement iteration over the > whole file. > > [1] https://www.mankier.com/2/ioctl_fideduperange Well, we can't change the semantics now because there could be programs that aren't expecting a nonzero return from a length == 0 dedupe, so like Christoph said, I'll just change generic/182 and make the VFS wrapper emulate the btrfs behavior so that any subsequent implementation won't hit this. I'll update the clone/clonerange manpages to mention the 0 -> EOF behavior. Would've been awesome if anyone had bothered to document the damn ioctls and write tests to call out these subtleties rather than leave the next implementer to clean up all the technical debt. I dunno, maybe there /is/ a secret cache of btrfs regression tests somewhere that I haven't found. <grumble> --D -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/14/2016 02:06 PM, Darrick J. Wong wrote: > On Wed, Jul 13, 2016 at 03:19:38PM +0200, David Sterba wrote: >> On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: >>> On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: >>>> Hey, Darrick, >>>> >>>> generic/182 is failing on Btrfs for me with the following output: >>>> >>>> --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 >>>> +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 >>>> @@ -1,12 +1,10 @@ >>>> QA output created by 182 >>>> Create the original files >>>> -dedupe: Extents did not match. >>>> f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 >>>> 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 >>>> 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk >>>> Compare against check files >>>> Make the original file almost dedup-able >>>> -dedupe: Extents did not match. >>>> f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 >>>> 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 >>>> 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk >>>> >>>> It looks like that test is checking that a dedupe with length == 0 is >>>> treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I >>>> can tell, it never did, but maybe I'm just confused. What was the >>>> behavior when you introduced that test? That seems like a reasonable >>>> thing to do, but I wanted to clear this up before changing/fixing Btrfs. >>> >>> It's a shortcut that we're introducing in the upcoming XFS implementation, >>> since it shares the same back end as clone/clonerange, which both have >>> this behavior. >> >> The support for zero length does not seem to be mentioned anywhere with >> the dedupe range ioctl [1], so the current implemetnation is "up to >> spec". That it should be valid is hidden in clone_verify_area where a >> zero length is substituted with OFFSET_MAX >> >> https://urldefense.proofpoint.com/v2/url?u=http-3A__lxr.free-2Delectrons.com_source_fs_read-5Fwrite.c-23L1607&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=ZymMvbZ2mZOYBKya3guibggSaaqOHZUqedhz0pT5PPc&e= >> >> So it looks like it's up to the implementation in the filesystem to >> handle that. As the btrfs ioctl was extent-based, a zero length extent >> does not make sense, so this case was not handled. But in your patch >> >> 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 >> btrfs: use new dedupe data function pointer >> >> it was suddenly expected to work. So the missing bits are either 'not >> supported' for zero length or actually implement iteration over the >> whole file. >> >> [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mankier.com_2_ioctl-5Ffideduperange&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=NYdHr9JyZZNKPLsOf_VmtZ-3X2B1azTYfyE4Lf1Fa5w&e= > > Well, we can't change the semantics now because there could be programs that > aren't expecting a nonzero return from a length == 0 dedupe, so like Christoph > said, I'll just change generic/182 and make the VFS wrapper emulate the btrfs > behavior so that any subsequent implementation won't hit this. > > I'll update the clone/clonerange manpages to mention the 0 -> EOF behavior. Its fine with me if we change btrfs to do the 0->EOF. It's a corner case I'm happy to include. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Jul 14, 2016 at 02:12:58PM -0400, Chris Mason wrote: > > > On 07/14/2016 02:06 PM, Darrick J. Wong wrote: > > On Wed, Jul 13, 2016 at 03:19:38PM +0200, David Sterba wrote: > > > On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > > > > On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > > > > > Hey, Darrick, > > > > > > > > > > generic/182 is failing on Btrfs for me with the following output: > > > > > > > > > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > > > > > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > > > > > @@ -1,12 +1,10 @@ > > > > > QA output created by 182 > > > > > Create the original files > > > > > -dedupe: Extents did not match. > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > > > > > Compare against check files > > > > > Make the original file almost dedup-able > > > > > -dedupe: Extents did not match. > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > > > > > > > > > It looks like that test is checking that a dedupe with length == 0 is > > > > > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > > > > > can tell, it never did, but maybe I'm just confused. What was the > > > > > behavior when you introduced that test? That seems like a reasonable > > > > > thing to do, but I wanted to clear this up before changing/fixing Btrfs. > > > > > > > > It's a shortcut that we're introducing in the upcoming XFS implementation, > > > > since it shares the same back end as clone/clonerange, which both have > > > > this behavior. > > > > > > The support for zero length does not seem to be mentioned anywhere with > > > the dedupe range ioctl [1], so the current implemetnation is "up to > > > spec". That it should be valid is hidden in clone_verify_area where a > > > zero length is substituted with OFFSET_MAX > > > > > > https://urldefense.proofpoint.com/v2/url?u=http-3A__lxr.free-2Delectrons.com_source_fs_read-5Fwrite.c-23L1607&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=ZymMvbZ2mZOYBKya3guibggSaaqOHZUqedhz0pT5PPc&e= > > > > > > So it looks like it's up to the implementation in the filesystem to > > > handle that. As the btrfs ioctl was extent-based, a zero length extent > > > does not make sense, so this case was not handled. But in your patch > > > > > > 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 > > > btrfs: use new dedupe data function pointer > > > > > > it was suddenly expected to work. So the missing bits are either 'not > > > supported' for zero length or actually implement iteration over the > > > whole file. > > > > > > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mankier.com_2_ioctl-5Ffideduperange&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=NYdHr9JyZZNKPLsOf_VmtZ-3X2B1azTYfyE4Lf1Fa5w&e= > > > > Well, we can't change the semantics now because there could be programs that > > aren't expecting a nonzero return from a length == 0 dedupe, so like Christoph > > said, I'll just change generic/182 and make the VFS wrapper emulate the btrfs > > behavior so that any subsequent implementation won't hit this. > > > > I'll update the clone/clonerange manpages to mention the 0 -> EOF behavior. > > Its fine with me if we change btrfs to do the 0->EOF. It's a corner case > I'm happy to include. > > -chris Yeah, I think it's a nice shortcut. Are there any programs which wouldn't want this, though? It's a milder sort of correctness problem since dedupe is "safe", but maybe there's some tool which is being dumb and trying to dedupe nothing.
On Thu, Jul 14, 2016 at 11:16:47AM -0700, Omar Sandoval wrote: > On Thu, Jul 14, 2016 at 02:12:58PM -0400, Chris Mason wrote: > > > > > > On 07/14/2016 02:06 PM, Darrick J. Wong wrote: > > > On Wed, Jul 13, 2016 at 03:19:38PM +0200, David Sterba wrote: > > > > On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > > > > > On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > > > > > > Hey, Darrick, > > > > > > > > > > > > generic/182 is failing on Btrfs for me with the following output: > > > > > > > > > > > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > > > > > > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > > > > > > @@ -1,12 +1,10 @@ > > > > > > QA output created by 182 > > > > > > Create the original files > > > > > > -dedupe: Extents did not match. > > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > > > > > > Compare against check files > > > > > > Make the original file almost dedup-able > > > > > > -dedupe: Extents did not match. > > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > > > > > > > > > > > It looks like that test is checking that a dedupe with length == 0 is > > > > > > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > > > > > > can tell, it never did, but maybe I'm just confused. What was the > > > > > > behavior when you introduced that test? That seems like a reasonable > > > > > > thing to do, but I wanted to clear this up before changing/fixing Btrfs. > > > > > > > > > > It's a shortcut that we're introducing in the upcoming XFS implementation, > > > > > since it shares the same back end as clone/clonerange, which both have > > > > > this behavior. > > > > > > > > The support for zero length does not seem to be mentioned anywhere with > > > > the dedupe range ioctl [1], so the current implemetnation is "up to > > > > spec". That it should be valid is hidden in clone_verify_area where a > > > > zero length is substituted with OFFSET_MAX > > > > > > > > https://urldefense.proofpoint.com/v2/url?u=http-3A__lxr.free-2Delectrons.com_source_fs_read-5Fwrite.c-23L1607&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=ZymMvbZ2mZOYBKya3guibggSaaqOHZUqedhz0pT5PPc&e= > > > > > > > > So it looks like it's up to the implementation in the filesystem to > > > > handle that. As the btrfs ioctl was extent-based, a zero length extent > > > > does not make sense, so this case was not handled. But in your patch > > > > > > > > 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 > > > > btrfs: use new dedupe data function pointer > > > > > > > > it was suddenly expected to work. So the missing bits are either 'not > > > > supported' for zero length or actually implement iteration over the > > > > whole file. > > > > > > > > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mankier.com_2_ioctl-5Ffideduperange&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=NYdHr9JyZZNKPLsOf_VmtZ-3X2B1azTYfyE4Lf1Fa5w&e= > > > > > > Well, we can't change the semantics now because there could be programs that > > > aren't expecting a nonzero return from a length == 0 dedupe, so like Christoph > > > said, I'll just change generic/182 and make the VFS wrapper emulate the btrfs > > > behavior so that any subsequent implementation won't hit this. > > > > > > I'll update the clone/clonerange manpages to mention the 0 -> EOF behavior. > > > > Its fine with me if we change btrfs to do the 0->EOF. It's a corner case > > I'm happy to include. > > > > -chris > > Yeah, I think it's a nice shortcut. Are there any programs which > wouldn't want this, though? It's a milder sort of correctness problem > since dedupe is "safe", but maybe there's some tool which is being dumb > and trying to dedupe nothing. <shrug> The only problems I can see here is some program that calls dedupe with a length == 0 /and/ doesn't expect a non-zero return value... or gets confused that bytes_deduped > 0. I don't think duperemove has either of those problems. Is that the only client? --D > > -- > Omar -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Jul 14, 2016 at 11:16:47AM -0700, Omar Sandoval wrote: > On Thu, Jul 14, 2016 at 02:12:58PM -0400, Chris Mason wrote: > > > > > > On 07/14/2016 02:06 PM, Darrick J. Wong wrote: > > > On Wed, Jul 13, 2016 at 03:19:38PM +0200, David Sterba wrote: > > > > On Tue, Jul 12, 2016 at 10:26:43PM -0700, Darrick J. Wong wrote: > > > > > On Mon, Jul 11, 2016 at 05:35:37PM -0700, Omar Sandoval wrote: > > > > > > Hey, Darrick, > > > > > > > > > > > > generic/182 is failing on Btrfs for me with the following output: > > > > > > > > > > > > --- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 > > > > > > +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 > > > > > > @@ -1,12 +1,10 @@ > > > > > > QA output created by 182 > > > > > > Create the original files > > > > > > -dedupe: Extents did not match. > > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 > > > > > > 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk > > > > > > Compare against check files > > > > > > Make the original file almost dedup-able > > > > > > -dedupe: Extents did not match. > > > > > > f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 > > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 > > > > > > 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk > > > > > > > > > > > > It looks like that test is checking that a dedupe with length == 0 is > > > > > > treated as a dedupe to EOF, but Btrfs doesn't do that [1]. As far as I > > > > > > can tell, it never did, but maybe I'm just confused. What was the > > > > > > behavior when you introduced that test? That seems like a reasonable > > > > > > thing to do, but I wanted to clear this up before changing/fixing Btrfs. > > > > > > > > > > It's a shortcut that we're introducing in the upcoming XFS implementation, > > > > > since it shares the same back end as clone/clonerange, which both have > > > > > this behavior. > > > > > > > > The support for zero length does not seem to be mentioned anywhere with > > > > the dedupe range ioctl [1], so the current implemetnation is "up to > > > > spec". That it should be valid is hidden in clone_verify_area where a > > > > zero length is substituted with OFFSET_MAX > > > > > > > > https://urldefense.proofpoint.com/v2/url?u=http-3A__lxr.free-2Delectrons.com_source_fs_read-5Fwrite.c-23L1607&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=ZymMvbZ2mZOYBKya3guibggSaaqOHZUqedhz0pT5PPc&e= > > > > > > > > So it looks like it's up to the implementation in the filesystem to > > > > handle that. As the btrfs ioctl was extent-based, a zero length extent > > > > does not make sense, so this case was not handled. But in your patch > > > > > > > > 2b3909f8a7fe94e0234850aa9d120cca15b6e1f7 > > > > btrfs: use new dedupe data function pointer > > > > > > > > it was suddenly expected to work. So the missing bits are either 'not > > > > supported' for zero length or actually implement iteration over the > > > > whole file. > > > > > > > > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mankier.com_2_ioctl-5Ffideduperange&d=CwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=CKo3CgE8Up_NBDdC9t7fCuwHwsdf6nZG2nKcl5-NqnI&s=NYdHr9JyZZNKPLsOf_VmtZ-3X2B1azTYfyE4Lf1Fa5w&e= > > > > > > Well, we can't change the semantics now because there could be programs that > > > aren't expecting a nonzero return from a length == 0 dedupe, so like Christoph > > > said, I'll just change generic/182 and make the VFS wrapper emulate the btrfs > > > behavior so that any subsequent implementation won't hit this. > > > > > > I'll update the clone/clonerange manpages to mention the 0 -> EOF behavior. > > > > Its fine with me if we change btrfs to do the 0->EOF. It's a corner case > > I'm happy to include. > > > > -chris > > Yeah, I think it's a nice shortcut. Are there any programs which > wouldn't want this, though? It's a milder sort of correctness problem > since dedupe is "safe", but maybe there's some tool which is being dumb > and trying to dedupe nothing. The only users of extent-same that I know of are duperemove and xfs_io. duperemove doesn't seem to send zero-length dedupe requests. xfs_io will if you tell it to, but the xfs_io feature is there primarily to run xfstests. Christoph has a valid point that we don't know the full set of users, so we could be breaking them by changing this aspect. OTOH this was an undocumented ioctl for quite a while... --D > > -- > Omar -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- tests/generic/182.out 2016-07-07 19:51:54.000000000 -0700 +++ /tmp/fixxfstests/xfstests/results//generic/182.out.bad 2016-07-11 17:28:28.230039216 -0700 @@ -1,12 +1,10 @@ QA output created by 182 Create the original files -dedupe: Extents did not match. f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2 69ad53078a16243d98e21d9f8704a071 TEST_DIR/test-182/file2.chk Compare against check files Make the original file almost dedup-able -dedupe: Extents did not match. f4820540fc0ac02750739896fe028d56 TEST_DIR/test-182/file1 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2 158d4e3578b94b89cbb44493a2110fb9 TEST_DIR/test-182/file2.chk