[libvirt PATCH 2/4] storage: convert to use virFileSetCOW

[Daniel P. Berrangé]

When disabling COW on individual files, we now use the virFileSetCOW
method. Note that this change has a slight semantic difference to the
old implementation.

The original code reported errors but returned success when disabling
COW failed.

With this new code, we will always report an error if the user requested
disabling of COW and we could not honour it, either because btrfs
returned an error, or because the filesystem is not btrfs.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/storage/storage_util.c | 27 +++++----------------------
 1 file changed, 5 insertions(+), 22 deletions(-)

diff --git a/src/storage/storage_util.c b/src/storage/storage_util.c
index ee048f02fe..2595162a61 100644
--- a/src/storage/storage_util.c
+++ b/src/storage/storage_util.c
@@ -28,9 +28,6 @@
 #ifdef __linux__
 # include <sys/ioctl.h>
 # include <linux/fs.h>
-# ifndef FS_NOCOW_FL
-#  define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
-# endif
 # define default_mount_opts "nodev,nosuid,noexec"
 #elif defined(__FreeBSD__)
 # define default_mount_opts "nosuid,noexec"
@@ -456,25 +453,11 @@ storageBackendCreateRaw(virStoragePoolObjPtr pool,
     }
     created = true;
 
-    if (vol->target.nocow) {
-#ifdef __linux__
-        int attr;
-
-        /* Set NOCOW flag. This is an optimisation for btrfs.
-         * The FS_IOC_SETFLAGS ioctl return value will be ignored since any
-         * failure of this operation should not block the volume creation.
-         */
-        if (ioctl(fd, FS_IOC_GETFLAGS, &attr) < 0) {
-            virReportSystemError(errno, "%s", _("Failed to get fs flags"));
-        } else {
-            attr |= FS_NOCOW_FL;
-            if (ioctl(fd, FS_IOC_SETFLAGS, &attr) < 0) {
-                virReportSystemError(errno, "%s",
-                                     _("Failed to set NOCOW flag"));
-            }
-        }
-#endif
-    }
+    /* NB, COW flag can only be toggled when the file is zero-size,
+     * so must go before the createRawFile call allocates payload */
+    if (vol->target.nocow &&
+        virFileSetCOW(vol->target.path, VIR_TRISTATE_BOOL_NO) < 0)
+        goto cleanup;
 
     if ((ret = createRawFile(fd, vol, inputvol, reflink_copy)) < 0)
         /* createRawFile already reported the exact error. */
-- 
2.26.2