Hi Brian, Thanks for the suggestion. Yes, the ioctl call that xfs_io makes is basically identical to the one the test makes, except it has the SYNC flag set. Adding this flag (or calling fsync) results in expected behaviour (mapped_extents > 0).
I assume that the bcachefs fiemap impl ignores unwritten data and only responds with flushed extents? I'm not sure if this is correct; for comparison, XFS, Btfs, zfs, and ext4, all return the extent map immediately after write without syncing. You're right that bcachefs seems to split extents that would be contiguous on some other FSs, but that's fine here. Thanks, Steve On Wed, 6 Dec 2023 at 01:53, Brian Foster <[email protected]> wrote: > > On Tue, Dec 05, 2023 at 04:26:40PM +1100, Steve Smith wrote: > > Hi, > > > > I'm doing some testing of xcp[1] against bcachefs, and having issues > > with fiemap. Using fiemap on both sparse and non-sparse files always > > returns `mapped_extents` of 0. The same tests on other extent-based > > FSs return non-zero extents, with consistent values. This is against > > -rc4 and master. > > > > I've broken the relevant tests (in Rust) out into a standalone crate > > if you want to reproduce: > > > > https://github.com/tarka/bcachefs-test > > > > The FS in question was created with a simple `bcachefs -L xcp-test > > /dev/sdh1`. > > > > Hi Steve, > > Well I'm not really familiar with xcp or your test harness here, but > have you checked the results you're seeing against known working tools? > For example, one of the subtests just seems to perform a simple write > followed by an fiemap check/assert for a single extent. That is roughly > equivalent to: > > # xfs_io -fc "pwrite 0 128k" -c "fiemap -v" ./file > wrote 131072/131072 bytes at offset 0 > 128 KiB, 32 ops; 0.0011 sec (108.790 MiB/sec and 27850.3046 ops/sec) > ./file: > EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS > 0: [0..127]: 339968..340095 128 0x0 > 1: [128..255]: 340096..340223 128 0x1 > > ... which mostly seems to DTRT. I have noticed in the past that bcachefs > fiemap seems to break extents into bucket size or some such segments, > regardless of contiguity, but this doesn't seem to be the issue you are > reporting here. I.e. an strace of the above shows the following for the > fiemap ioctl(): > > ioctl(3, FS_IOC_FIEMAP, {fm_start=0, fm_length=18446744073709551615, > fm_flags=FIEMAP_FLAG_SYNC, fm_extent_count=32} => {fm_flags=FIEMAP_FLAG_SYNC, > fm_mapped_extents=2, ...}) = 0 > > ... which shows fm_mapped_extents == 2. Hm? > > Brian > > > Cheers, > > Steve > > > > [1]: https://github.com/tarka/xcp > > >
