[Qemu-devel] [PATCH v5] raw-posix: add discard support

[Christoph Hellwig <hch@lst.de>]

Add support to discard blocks in a raw image residing on an XFS filesystem
by calling the XFS_IOC_UNRESVSP64 ioctl to punch holes.  Support for other
hole punching mechanisms can be added when they become available.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: qemu/block/raw-posix.c
===================================================================
--- qemu.orig/block/raw-posix.c	2010-12-17 11:30:21.455262819 +0100
+++ qemu/block/raw-posix.c	2010-12-17 11:32:00.131003705 +0100
@@ -69,6 +69,10 @@
 #include <sys/diskslice.h>
 #endif
 
+#ifdef CONFIG_XFS
+#include <xfs/xfs.h>
+#endif
+
 //#define DEBUG_FLOPPY
 
 //#define DEBUG_BLOCK
@@ -120,6 +124,9 @@ typedef struct BDRVRawState {
 #endif
     uint8_t *aligned_buf;
     unsigned aligned_buf_size;
+#ifdef CONFIG_XFS
+    bool is_xfs : 1;
+#endif
 } BDRVRawState;
 
 static int fd_open(BlockDriverState *bs);
@@ -196,6 +203,12 @@ static int raw_open_common(BlockDriverSt
 #endif
     }
 
+#ifdef CONFIG_XFS
+    if (platform_test_xfs_fd(s->fd)) {
+        s->is_xfs = 1;
+    }
+#endif
+
     return 0;
 
 out_free_buf:
@@ -740,6 +753,37 @@ static int raw_flush(BlockDriverState *b
     return qemu_fdatasync(s->fd);
 }
 
+#ifdef CONFIG_XFS
+static int xfs_discard(BDRVRawState *s, int64_t sector_num, int nb_sectors)
+{
+    struct xfs_flock64 fl;
+
+    memset(&fl, 0, sizeof(fl));
+    fl.l_whence = SEEK_SET;
+    fl.l_start = sector_num << 9;
+    fl.l_len = (int64_t)nb_sectors << 9;
+
+    if (xfsctl(NULL, s->fd, XFS_IOC_UNRESVSP64, &fl) < 0) {
+        DEBUG_BLOCK_PRINT("cannot punch hole (%s)\n", strerror(errno));
+        return -errno;
+    }
+
+    return 0;
+}
+#endif
+
+static int raw_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors)
+{
+#ifdef CONFIG_XFS
+    BDRVRawState *s = bs->opaque;
+
+    if (s->is_xfs) {
+        return xfs_discard(s, sector_num, nb_sectors);
+    }
+#endif
+
+    return 0;
+}
 
 static QEMUOptionParameter raw_create_options[] = {
     {
@@ -761,6 +805,7 @@ static BlockDriver bdrv_file = {
     .bdrv_close = raw_close,
     .bdrv_create = raw_create,
     .bdrv_flush = raw_flush,
+    .bdrv_discard = raw_discard,
 
     .bdrv_aio_readv = raw_aio_readv,
     .bdrv_aio_writev = raw_aio_writev,
Index: qemu/configure
===================================================================
--- qemu.orig/configure	2010-12-17 11:30:21.468254368 +0100
+++ qemu/configure	2010-12-17 11:30:40.080023610 +0100
@@ -288,6 +288,7 @@ xen=""
 linux_aio=""
 attr=""
 vhost_net=""
+xfs=""
 
 gprof="no"
 debug_tcg="no"
@@ -1399,6 +1400,27 @@ EOF
 fi
 
 ##########################################
+# xfsctl() probe, used for raw-posix
+if test "$xfs" != "no" ; then
+  cat > $TMPC << EOF
+#include <xfs/xfs.h>
+int main(void)
+{
+    xfsctl(NULL, 0, 0, NULL);
+    return 0;
+}
+EOF
+  if compile_prog "" "" ; then
+    xfs="yes"
+  else
+    if test "$xfs" = "yes" ; then
+      feature_not_found "xfs"
+    fi
+    xfs=no
+  fi
+fi
+
+##########################################
 # vde libraries probe
 if test "$vde" != "no" ; then
   vde_libs="-lvdeplug"
@@ -2403,6 +2425,7 @@ echo "Trace backend     $trace_backend"
 echo "Trace output file $trace_file-<pid>"
 echo "spice support     $spice"
 echo "rbd support       $rbd"
+echo "xfsctl support    $xfs"
 
 if test $sdl_too_old = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -2548,6 +2571,9 @@ fi
 if test "$uuid" = "yes" ; then
   echo "CONFIG_UUID=y" >> $config_host_mak
 fi
+if test "$xfs" = "yes" ; then
+  echo "CONFIG_XFS=y" >> $config_host_mak
+fi
 qemu_version=`head $source_path/VERSION`
 echo "VERSION=$qemu_version" >>$config_host_mak
 echo "PKGVERSION=$pkgversion" >>$config_host_mak