block/raw-posix: Fix disk corruption in try_fiemap

Using fiemap without FIEMAP_FLAG_SYNC is a known corrupter.

Add the FIEMAP_FLAG_SYNC flag to the FS_IOC_FIEMAP ioctl.  This has
the downside of significantly reducing performance.
Reported-By: NMichael Steffens <michael_steffens@posteo.de>
Signed-off-by: NTony Breeds <tony@bakeyournoodle.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Pádraig Brady <pbrady@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/raw-posix.c

@@ -1482,7 +1482,7 @@ static int64_t try_fiemap(BlockDriverState *bs, off_t start, off_t *data,
 
     f.fm.fm_start = start;
     f.fm.fm_length = (int64_t)nb_sectors * BDRV_SECTOR_SIZE;
-    f.fm.fm_flags = 0;
+    f.fm.fm_flags = FIEMAP_FLAG_SYNC;
     f.fm.fm_extent_count = 1;
     f.fm.fm_reserved = 0;
     if (ioctl(s->fd, FS_IOC_FIEMAP, &f) == -1) {