On 28.11.2017 03:47, Darrick J. Wong wrote: > On Mon, Nov 27, 2017 at 09:44:34AM -0800, Darrick J. Wong wrote: >> On Thu, Nov 23, 2017 at 01:40:03PM +0200, Nikolay Borisov wrote: >>> For file extents xfs currently calls xfs_bmapi_read with flag set to 0, >>> meaning extents are going to be truncated to the requested range. Since the >>> same codepath is used for fiemap this means xfs is special in that regard, since >>> other filesystems (ext4/btrfs) do not trim extents for fiemap. Make the behavior >>> consistent by always passing XFS_BMAPI_ENTIRE. A full xfstest run validated that >>> this doesn't regress on ordinary read/write IO. >>> >>> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx> >> >> Looks ok, will also test... >> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > ...and now withdrawn. > > Looking at iomap_apply, it seems we call ->iomap_begin, and at line 73 we > trim an iomap that is longer than the range we requested: > > /* > * Cut down the length to the one actually provided by the filesystem, > * as it might not be able to give us the whole size that we requested. > */ > if (iomap.offset + iomap.length < pos + length) > length = iomap.offset + iomap.length - pos; This actually trims the requested length to match what iomap has given is. I.e if we request a range between [50, 100] (length 50, offset 50) but iomap returns [40,60] (offset 40, length 20) then the trimmer range is : [50, 10]. SO it's actually trimming the requested range against what was actually returned by the filesystem not the other way around. > > However, we do not trim the beginning off an iomap that starts before > the 'pos' we passed to ->iomap_begin, so we're left with an iomap that > can begin before the range. > > FWIW I ran xfstests (like I told you to on IRC) and saw regressions > in a whole bunch of tests: > > generic/170 generic/287 generic/295 generic/326 generic/330 generic/333 > generic/372 xfs/214 xfs/237 xfs/249 xfs/258 xfs/346 xfs/420 xfs/421 > > From a brief glance it looks as though most of the iomap_apply'ers > try to trim the iomap before using it, but clearly there's something > wrong here. > > --D > >> >>> --- >>> fs/xfs/xfs_iomap.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c >>> index f179bdf1644d..8942324a4d3d 100644 >>> --- a/fs/xfs/xfs_iomap.c >>> +++ b/fs/xfs/xfs_iomap.c >>> @@ -1008,7 +1008,7 @@ xfs_file_iomap_begin( >>> end_fsb = XFS_B_TO_FSB(mp, offset + length); >>> >>> error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap, >>> - &nimaps, 0); >>> + &nimaps, XFS_BMAPI_ENTIRE); >>> if (error) >>> goto out_unlock; >>> >>> -- >>> 2.7.4 >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
