block: introduce preallocate filter

It's intended to be inserted between format and protocol nodes to
preallocate additional space (expanding protocol file) on writes
crossing EOF. It improves performance for file-systems with slow
allocation.

Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
[mreitz: Two comment fixes, and bumped the version from 5.2 to 6.0]
Signed-off-by: Max Reitz <[email protected]>

Author: Vladimir Sementsov-Ogievskiy

block/meson.build

@@ -12,6 +12,7 @@ block_ss.add(files(
   'block-copy.c',
   'commit.c',
   'copy-on-read.c',
+  'preallocate.c',
   'create.c',
   'crypto.c',
   'dirty-bitmap.c',