Hello everyone,

The test below creates a sparse file and then fills a hole with
O_DIRECT.  As far as I can tell from reading generic_osync_inode, the
filesystem metadata is only forced to disk if i_size changes during the
file write.  I've tested ext3, xfs and reiserfs and they all skip the
commit when filling holes.

I would argue that filling holes via O_DIRECT is supposed to commit the
metadata required to find those file blocks later.  At least on ext3,
O_SYNC does force a commit on fill holes  (haven't tested others).

So, is the current behavior a bug or a feature?

dd if=/dev/zero of=foo bs=1M seek=1 count=1 oflag=direct

hexdump foo | head -n 2
0000000 62b1 ea2d 73e8 c64f f5ef 1af5 dd09 8ccd
0000010 75ec 9581 e0ea ae9b e28f b76d a700 4d5b

dd if=/dev/urandom of=foo bs=4k count=1 conv=notrunc oflag=direct
reboot -nf

(after reboot)

hexdump foo
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
0200000

-chris


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