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virtiofsd: Fix data corruption with O_APPEND write in writeback mode 

When writeback mode is enabled (-o writeback), O_APPEND handling is
done in kernel. Therefore virtiofsd clears O_APPEND flag when open.
Otherwise O_APPEND flag takes precedence over pwrite() and write
data may corrupt.

Currently clearing O_APPEND flag is done in lo_open(), but we also
need the same operation in lo_create(). So, factor out the flag
update operation in lo_open() to update_open_flags() and call it
in both lo_open() and lo_create().

This fixes the failure of xfstest generic/069 in writeback mode
(which tests O_APPEND write data integrity).

Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Misono Tomohiro 2019-10-23 21:25:23 +09:00 committed by Dr. David Alan Gilbert
parent 65da453980
commit 8e4e41e39e
1 changed files with 33 additions and 33 deletions
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66
tools/virtiofsd/passthrough_ll.c
View File

@ -1692,6 +1692,37 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino,
fuse_reply_err(req, 0);
}
static void update_open_flags(int writeback, struct fuse_file_info *fi)
{
/*
* With writeback cache, kernel may send read requests even
* when userspace opened write-only
*/
if (writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {
fi->flags &= ~O_ACCMODE;
fi->flags |= O_RDWR;
}
/*
* With writeback cache, O_APPEND is handled by the kernel.
* This breaks atomicity (since the file may change in the
* underlying filesystem, so that the kernel's idea of the
* end of the file isn't accurate anymore). In this example,
* we just accept that. A more rigorous filesystem may want
* to return an error here
*/
if (writeback && (fi->flags & O_APPEND)) {
fi->flags &= ~O_APPEND;
}
/*
* O_DIRECT in guest should not necessarily mean bypassing page
* cache on host as well. If somebody needs that behavior, it
* probably should be a configuration knob in daemon.
*/
fi->flags &= ~O_DIRECT;
}
static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
mode_t mode, struct fuse_file_info *fi)
{
@ -1721,12 +1752,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
goto out;
}
/*
* O_DIRECT in guest should not necessarily mean bypassing page
* cache on host as well. If somebody needs that behavior, it
* probably should be a configuration knob in daemon.
*/
fi->flags &= ~O_DIRECT;
update_open_flags(lo->writeback, fi);
fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
mode);
@ -1936,33 +1962,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino,
fi->flags);
/*
* With writeback cache, kernel may send read requests even
* when userspace opened write-only
*/
if (lo->writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {
fi->flags &= ~O_ACCMODE;
fi->flags |= O_RDWR;
}
/*
* With writeback cache, O_APPEND is handled by the kernel.
* This breaks atomicity (since the file may change in the
* underlying filesystem, so that the kernel's idea of the
* end of the file isn't accurate anymore). In this example,
* we just accept that. A more rigorous filesystem may want
* to return an error here
*/
if (lo->writeback && (fi->flags & O_APPEND)) {
fi->flags &= ~O_APPEND;
}
/*
* O_DIRECT in guest should not necessarily mean bypassing page
* cache on host as well. If somebody needs that behavior, it
* probably should be a configuration knob in daemon.
*/
fi->flags &= ~O_DIRECT;
update_open_flags(lo->writeback, fi);
sprintf(buf, "%i", lo_fd(req, ino));
fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);