block/raw-posix: use seek_hole ahead of fiemap

try_fiemap() uses FIEMAP_FLAG_SYNC which has a significant performance
impact.

Prefer seek_hole() over fiemap() to avoid this impact where possible.
seek_hole is more widely used and, arguably, has potential to be
optimised in the kernel.

Reported-By: Michael Steffens <michael_steffens@posteo.de>
Signed-off-by: Tony 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: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/raw-posix.c b/block/raw-posix.c
index d672c73..eb76f0e 100644 (file)
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1571,9 +1571,9 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
 
     start = sector_num * BDRV_SECTOR_SIZE;
 
-    ret = try_fiemap(bs, start, &data, &hole, nb_sectors, pnum);
+    ret = try_seek_hole(bs, start, &data, &hole, pnum);
     if (ret < 0) {
-        ret = try_seek_hole(bs, start, &data, &hole, pnum);
+        ret = try_fiemap(bs, start, &data, &hole, nb_sectors, pnum);
         if (ret < 0) {
             /* Assume everything is allocated. */
             data = 0;