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author | Theodore Ts'o <tytso@mit.edu> | 2016-06-06 23:04:43 -0400 |
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committer | Theodore Ts'o <tytso@mit.edu> | 2016-06-06 23:04:43 -0400 |
commit | 127e2291bf02c39bba58eb9b8096a2670319a5bb (patch) | |
tree | f5ea01341e61431ec5b5236900208ae26b5c6948 /lib | |
parent | be5ce275259e6216b618d3900786b365669a0b42 (diff) | |
download | e2fsprogs-127e2291bf02c39bba58eb9b8096a2670319a5bb.tar.gz |
libext2fs: fix Direct I/O fallback code so it implements RMW correctly
There is a bug in Unix I/O manager where if an aligned I/O is
required, it does not correctly do the read-modify-write cycle
correctly. Specifically, it was not doing an lseek between the read
and the write calls, so the update was going to block N+1 instead of
block N. Oops.
Fortunately in practice we almost never use this fallback path, so
file systems weren't getting horribly corrupted, because (a) we almost
never use Direct I/O in e2fsprogs, at least not by default, and (b)
when we do the buffers end up being aligned anyway, so it's OK.
We only noticed this because the new Undo I/O manager in e2fsprogs
1.43 was doing unaligned I/O and FreeBSD requires that I/O requests be
aligned even if you are not doing Direct I/O, and the e2undo
regression tests were all failing as a result.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/ext2fs/unix_io.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c index 23f22e30f..4403aa0e6 100644 --- a/lib/ext2fs/unix_io.c +++ b/lib/ext2fs/unix_io.c @@ -282,6 +282,10 @@ static errcode_t raw_write_blk(io_channel channel, if (size > channel->block_size) actual = channel->block_size; memcpy(data->bounce, buf, actual); + if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) { + retval = errno ? errno : EXT2_ET_LLSEEK_FAILED; + goto error_out; + } actual = write(data->dev, data->bounce, channel->block_size); if (actual != channel->block_size) goto short_write; |