[Qemu-devel] [PATCH] raw-posix: Support discard on more filesystems

[Kusanagi Kouichi <slash@ac.auone-net.jp>]

Linux 2.6.38 introduced the filesystem independent interface to
deallocate part of a file. As of Linux 3.7, btrfs, ext4, ocfs2,
tmpfs and xfs support it.

Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
---
 block/raw-posix.c |   22 ++++++++++++++++++++--
 configure         |   19 +++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 87d888e..66ba0b5 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -59,6 +59,9 @@
 #ifdef CONFIG_FIEMAP
 #include <linux/fiemap.h>
 #endif
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+#include <linux/falloc.h>
+#endif
 #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
 #include <sys/disk.h>
 #include <sys/cdio.h>
@@ -1098,15 +1101,30 @@ static int xfs_discard(BDRVRawState *s, int64_t sector_num, int nb_sectors)
 static coroutine_fn int raw_co_discard(BlockDriverState *bs,
     int64_t sector_num, int nb_sectors)
 {
-#ifdef CONFIG_XFS
+#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_XFS)
     BDRVRawState *s = bs->opaque;
+#endif
+    int ret = 0;
 
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+    do {
+        if (fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                      sector_num << BDRV_SECTOR_BITS,
+                      nb_sectors << BDRV_SECTOR_BITS) == 0) {
+            return 0;
+        }
+    } while (errno == EINTR);
+
+    ret = -errno;
+#endif
+
+#ifdef CONFIG_XFS
     if (s->is_xfs) {
         return xfs_discard(s, sector_num, nb_sectors);
     }
 #endif
 
-    return 0;
+    return ret;
 }
 
 static QEMUOptionParameter raw_create_options[] = {
diff --git a/configure b/configure
index 837a84a..ff2e373 100755
--- a/configure
+++ b/configure
@@ -2576,6 +2576,22 @@ if compile_prog "" "" ; then
   fallocate=yes
 fi
 
+# check for fallocate hole punching
+fallocate_punch_hole=no
+cat > $TMPC << EOF
+#include <fcntl.h>
+#include <linux/falloc.h>
+
+int main(void)
+{
+    fallocate(0, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, 0);
+    return 0;
+}
+EOF
+if compile_prog "" "" ; then
+  fallocate_punch_hole=yes
+fi
+
 # check for sync_file_range
 sync_file_range=no
 cat > $TMPC << EOF
@@ -3485,6 +3501,9 @@ fi
 if test "$fallocate" = "yes" ; then
   echo "CONFIG_FALLOCATE=y" >> $config_host_mak
 fi
+if test "$fallocate_punch_hole" = "yes" ; then
+  echo "CONFIG_FALLOCATE_PUNCH_HOLE=y" >> $config_host_mak
+fi
 if test "$sync_file_range" = "yes" ; then
   echo "CONFIG_SYNC_FILE_RANGE=y" >> $config_host_mak
 fi
-- 
1.7.10.4