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... -Eric
