[Qemu-devel] [PATCH 6/7] block/raw-posix: call plain fallocate in handle_aiocb_write_zeroes

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

There is a possibility that we are extending our image and thus writing
zeroes beyond the end of the file. In this case we do not need to care
about the hole to make sure that there is no data in the file under
this offset (pre-condition to fallocate(0) to work). We could simply call
fallocate(0).

This improves the performance of writing zeroes even on really old
platforms which do not have even FALLOC_FL_PUNCH_HOLE.

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 | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index c039bef..fa05239 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -60,7 +60,7 @@
 #define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
 #endif
 #endif
-#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_FALLOCATE_ZERO_RANGE)
+#ifdef CONFIG_FALLOCATE
 #include <linux/falloc.h>
 #endif
 #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
@@ -902,7 +902,7 @@ static int translate_err(int err)
     return err;
 }
 
-#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_FALLOCATE_ZERO_RANGE)
+#ifdef CONFIG_FALLOCATE
 static int do_fallocate(int fd, int mode, off_t offset, off_t len)
 {
     do {
@@ -981,6 +981,12 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
     }
 #endif
 
+#ifdef CONFIG_FALLOCATE
+    if (aiocb->aio_offset >= aiocb->bs->total_sectors << BDRV_SECTOR_BITS) {
+        return do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
+    }
+#endif
+
     s->has_write_zeroes = false;
     return ret;
 }
-- 
1.9.1