At 04/07/2017 11:48 PM, Eric Sandeen wrote:
On 4/7/17 10:42 AM, Darrick J. Wong wrote:
On Fri, Apr 07, 2017 at 01:02:58PM +0800, Eryu Guan wrote:
On Thu, Apr 06, 2017 at 11:28:01AM -0500, Eric Sandeen wrote:
On 4/6/17 11:26 AM, Theodore Ts'o wrote:
On Wed, Apr 05, 2017 at 10:35:26AM +0800, Eryu Guan wrote:
Test fails with ext3/2 when driving with ext4 driver, fiemap changed
after umount/mount cycle, then changed back to original result after
sleeping some time. An ext4 bug? (cc'ed linux-ext4 list.)
I haven't had time to look at this, but I'm not sure this test is a
reasonable one on the face of it.
A file system may choose to optimize a file's extent tree for whatever
reason it wants, whenever it wants, including on an unmount --- and
that would not be an invalid thing to do. So to have an xfstests that
causes a test failure if a file system were to, say, do some cleanup
at mount or unmount time, or when the file is next opened, to merge
adjacent extents together (and hence change what is returned by
FIEMAP) might be strange, or even weird --- but is this any of user
space's business? Or anything we want to enforce as wrong wrong wrong
by xfstests?
So I was asking for a review from ext4 side instead of queuing it for
next xfstests update :)
In general FIEMAP can return pretty much whatever it wants, which
usually means that it won't report extents larger than the underlying
block mapping extents, though as we've seen it can split a single
on-disk extent into multiple FIEMAP records for the purpose of reporting
sharedness.
For ext3 I'm wondering if it's the case that the first time we FIEMAP an
indirect map file we see a possibly-merged version of whatever's in the
particular leaf node we land in; then that information gets cached &
merged with other records in the extent status tree, such that
subsequent FIEMAP calls see longer extents than the first time around.
I had the same question. If the exact behavior isn't defined anywhere,
I don't know what we can be testing, TBH.
Agreed, I was about to ask for the expected behavior today if there was
no new review comments on this patch.
I think the expected behavior is that any behavior is expected. :(
I suppose that if any particular filesystem wants to enforce stricter
rules for its own fiemap interface, that could be done in a
filesystem-specific test...
Well, then some test cases need to be moved from generic to filesystem
specified test, and some filsystems will have similar test cases.
I think it's a hell for maintainer to keep all these test cases consistent.
This is not the first time Btrfs failed to pass reflink and fiemap test
designed for xfs though.
Btrfs does skip some generic test case originally designed for xfs, like
generic/372.
But most of the time, xfs and btrfs can get consistent result.
And for btrfs side, we already have such fix now:
https://patchwork.kernel.org/patch/9668721/
It's OK that any fs can have either own fiemap behavior, but if it's a
not big fix and the behavior itself is somewhat wired, why not joining
the common behavior?
Thanks,
Qu
-Eric
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