[Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files

["Denis V. Lunev" <den@openvz.org>]

fallocate() works fine and could handle properly with arbitrary size
requests. There is no sense to reduce the amount of space to fallocate.
The bigger is the size, the better is the performance as the amount of
journal updates is reduced.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Peter Lieven <pl@kamp.de>
CC: Fam Zheng <famz@redhat.com>
---
 block/raw-posix.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index fa05239..e0b35c9 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -292,6 +292,20 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp)
     }
 }
 
+static void raw_probe_max_write_zeroes(BlockDriverState *bs)
+{
+    BDRVRawState *s = bs->opaque;
+    struct stat st;
+
+    if (fstat(s->fd, &st) < 0) {
+        return; /* no problem, keep default value */
+    }
+    if (!S_ISREG(st.st_mode) || !s->discard_zeroes) {
+        return;
+    }
+    bs->bl.max_write_zeroes = INT_MAX;
+}
+
 static void raw_parse_flags(int bdrv_flags, int *open_flags)
 {
     assert(open_flags != NULL);
@@ -598,6 +612,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
     /* Fail already reopen_prepare() if we can't get a working O_DIRECT
      * alignment with the new fd. */
     if (raw_s->fd != -1) {
+        raw_probe_max_write_zeroes(state->bs);
         raw_probe_alignment(state->bs, raw_s->fd, &local_err);
         if (local_err) {
             qemu_close(raw_s->fd);
@@ -651,6 +666,8 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
 
     raw_probe_alignment(bs, s->fd, errp);
     bs->bl.opt_mem_alignment = s->buf_align;
+
+    raw_probe_max_write_zeroes(bs);
 }
 
 static ssize_t handle_aiocb_ioctl(RawPosixAIOData *aiocb)
-- 
1.9.1