[libvirt] [PATCH v2] ZFS: Support sparse volumes
By default, `zfs create -V ...` reserves space for the entire volsize,
plus some extra (which attempts to account for overhead).
If `zfs create -s -V ...` is used instead, zvols are (fully) sparse.
A middle ground (partial allocation) can be achieved with
`zfs create -s -o refreservation=... -V ...`. Both libvirt and ZFS
support this approach, so the ZFS storage backend should support it.
Signed-off-by: Richard Laager <rlaager(a)wiktel.com>
---
Notes:
This version does not clamp allocation to capacity.
src/storage/storage_backend_zfs.c | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/src/storage/storage_backend_zfs.c b/src/storage/storage_backend_zfs.c
index 5238ecc..4d04a80 100644
--- a/src/storage/storage_backend_zfs.c
+++ b/src/storage/storage_backend_zfs.c
@@ -112,7 +112,7 @@ virStorageBackendZFSParseVol(virStoragePoolObjPtr pool,
if (!(tokens = virStringSplitCount(volume_string, "\t", 0, &count)))
return -1;
- if (count != 2)
+ if (count != 3)
goto cleanup;
if (!(name_tokens = virStringSplit(tokens[0], "/", 2)))
@@ -151,6 +151,15 @@ virStorageBackendZFSParseVol(virStoragePoolObjPtr pool,
goto cleanup;
}
+ if (virStrToLong_ull(tokens[2], NULL, 10, &volume->target.allocation) < 0)
{
+ virReportError(VIR_ERR_INTERNAL_ERROR,
+ "%s", _("malformed refreservation
reported"));
+ goto cleanup;
+ }
+
+ if (volume->target.allocation < volume->target.capacity)
+ volume->target.sparse = true;
+
if (is_new_vol &&
VIR_APPEND_ELEMENT(pool->volumes.objs,
pool->volumes.count,
@@ -190,7 +199,7 @@ virStorageBackendZFSFindVols(virStoragePoolObjPtr pool,
cmd = virCommandNewArgList(ZFS,
"list", "-Hp",
"-t", "volume", "-r",
- "-o", "name,volsize",
+ "-o", "name,volsize,refreservation",
pool->def->source.name,
NULL);
virCommandSetOutputBuffer(cmd, &volumes_list);
@@ -329,15 +338,28 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
goto cleanup;
/**
* $ zfs create -o volmode=dev -V 10240K test/volname
+ * $ zfs create -o volmode=dev -s -V 10240K test/volname
+ * $ zfs create -o volmode=dev -s -o refreservation=1024K -V 10240K test/volname
*
* -o volmode=dev -- we want to get volumes exposed as cdev
* devices. If we don't specify that zfs
* will lookup vfs.zfs.vol.mode sysctl value
+ * -s -- create a sparse volume
+ * -o refreservation -- reserve the specified amount of space
* -V -- tells to create a volume with the specified size
*/
cmd = virCommandNewArgList(ZFS, "create", NULL);
if (volmode_needed)
virCommandAddArgList(cmd, "-o", "volmode=dev", NULL);
+ if (vol->target.capacity != vol->target.allocation) {
+ virCommandAddArg(cmd, "-s");
+ if (vol->target.allocation > 0) {
+ virCommandAddArg(cmd, "-o");
+ virCommandAddArgFormat(cmd, "refreservation=%lluK",
+ VIR_DIV_UP(vol->target.allocation, 1024));
+ }
+ vol->target.sparse = true;
+ }
virCommandAddArg(cmd, "-V");
virCommandAddArgFormat(cmd, "%lluK",
VIR_DIV_UP(vol->target.capacity, 1024));
--
2.1.4