From 127e2291bf02c39bba58eb9b8096a2670319a5bb Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 6 Jun 2016 23:04:43 -0400 Subject: [PATCH] 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 --- lib/ext2fs/unix_io.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c index 23f22e3..4403aa0 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; -- 1.8.3.1