[Qemu-devel] [PATCH 4/7] block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes

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

This efficiently writes zeroes on Linux if the kernel is capable enough.
FALLOC_FL_ZERO_RANGE correctly handles all cases, including and not
including file expansion.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Max Reitz <mreitz@redhat.com>
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 | 15 +++++++++++++--
 configure         | 19 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index d3910fd..5a777e7 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
-#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_FALLOCATE_ZERO_RANGE)
 #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)
+#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_FALLOCATE_ZERO_RANGE)
 static int do_fallocate(int fd, int mode, off_t offset, off_t len)
 {
     do {
@@ -954,6 +954,17 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
     }
 #endif
 
+#ifdef CONFIG_FALLOCATE_ZERO_RANGE
+    if (s->has_write_zeroes) {
+        int ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
+                               aiocb->aio_offset, aiocb->aio_nbytes);
+        if (ret == 0 || ret != -ENOTSUP) {
+            return ret;
+        }
+        s->has_write_zeroes = false;
+    }
+#endif
+
     return -ENOTSUP;
 }
 
diff --git a/configure b/configure
index f185dd0..e00e03a 100755
--- a/configure
+++ b/configure
@@ -3335,6 +3335,22 @@ if compile_prog "" "" ; then
   fallocate_punch_hole=yes
 fi
 
+# check that fallocate supports range zeroing inside the file
+fallocate_zero_range=no
+cat > $TMPC << EOF
+#include <fcntl.h>
+#include <linux/falloc.h>
+
+int main(void)
+{
+    fallocate(0, FALLOC_FL_ZERO_RANGE, 0, 0);
+    return 0;
+}
+EOF
+if compile_prog "" "" ; then
+  fallocate_zero_range=yes
+fi
+
 # check for posix_fallocate
 posix_fallocate=no
 cat > $TMPC << EOF
@@ -4567,6 +4583,9 @@ fi
 if test "$fallocate_punch_hole" = "yes" ; then
   echo "CONFIG_FALLOCATE_PUNCH_HOLE=y" >> $config_host_mak
 fi
+if test "$fallocate_zero_range" = "yes" ; then
+  echo "CONFIG_FALLOCATE_ZERO_RANGE=y" >> $config_host_mak
+fi
 if test "$posix_fallocate" = "yes" ; then
   echo "CONFIG_POSIX_FALLOCATE=y" >> $config_host_mak
 fi
-- 
1.9.1