[libvirt] [PATCH 1/2] storage: zfs: enable on Linux

[Roman Bogorodskiy]

ZFS-on-Linux implementation of ZFS starting with version 0.6.4
contains all the features we use, so there's no reason to limit
libvirt ZFS storage backend to FreeBSD only.

There's still one difference between these implementations: ZFS on
FreeBSD requires to set 'volmode' option to 'dev' when creating
volumes, while ZFS-on-Linux does not need that.

Handle it by checking if 'volmode' option is needed by parsing usage
information of the 'zfs get' command.
---
 configure.ac                      |  8 ------
 src/storage/storage_backend_zfs.c | 51 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 10 deletions(-)

diff --git a/configure.ac b/configure.ac
index a566f5b..d768341 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2005,14 +2005,6 @@ if test "$with_storage_gluster" = "yes"; then
 fi
 AM_CONDITIONAL([WITH_STORAGE_GLUSTER], [test "$with_storage_gluster" = "yes"])
 
-if test "$with_storage_zfs" = "check"; then
-    with_storage_zfs=$with_freebsd
-fi
-
-if test "$with_storage_zfs" = "yes" && test "$with_freebsd" = "no"; then
-    AC_MSG_ERROR([The ZFS storage driver can be enabled on FreeBSD only.])
-fi
-
 if test "$with_storage_zfs" = "yes" ||
    test "$with_storage_zfs" = "check"; then
   AC_PATH_PROG([ZFS], [zfs], [], [$PATH:/sbin:/usr/sbin])
diff --git a/src/storage/storage_backend_zfs.c b/src/storage/storage_backend_zfs.c
index cb2662a..6bf7963 100644
--- a/src/storage/storage_backend_zfs.c
+++ b/src/storage/storage_backend_zfs.c
@@ -39,6 +39,47 @@ VIR_LOG_INIT("storage.storage_backend_zfs");
  *       for size, show just a number instead of 2G etc
  */
 
+/**
+ * virStorageBackendZFSVolModeNeeded:
+ *
+ * Checks if it's necessary to specify 'volmode' (i.e. that
+ * we're working with BSD ZFS implementation).
+ *
+ * Returns 1 if 'volmode' is need, 0 if not needed, -1 on error
+ */
+static int
+virStorageBackendZFSVolModeNeeded(void)
+{
+    virCommandPtr cmd = NULL;
+    int ret = -1, exit = -1;
+    char *error = NULL;
+
+    /* 'zfs get' without arguments prints out
+     * usage information to stderr, including
+     * list of supported options, and exits with
+     * exit code 2
+     */
+    cmd = virCommandNewArgList(ZFS, "get", NULL);
+    virCommandAddEnvString(cmd, "LC_ALL=C");
+    virCommandSetErrorBuffer(cmd, &error);
+
+    ret = virCommandRun(cmd, &exit);
+    if ((ret < 0) || (exit != 2)) {
+        VIR_WARN("Command 'zfs get' either failed "
+                 "to run or exited with unexpected status");
+        goto cleanup;
+    }
+
+    if (strstr(error, " volmode "))
+        ret = 1;
+    else
+        ret = 0;
+
+ cleanup:
+    virCommandFree(cmd);
+    VIR_FREE(error);
+    return ret;
+}
 
 static int
 virStorageBackendZFSCheckPool(virStoragePoolObjPtr pool ATTRIBUTE_UNUSED,
@@ -258,6 +299,7 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
 {
     virCommandPtr cmd = NULL;
     int ret = -1;
+    int volmode_needed = -1;
 
     vol->type = VIR_STORAGE_VOL_BLOCK;
 
@@ -273,6 +315,9 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
     if (VIR_STRDUP(vol->key, vol->target.path) < 0)
         goto cleanup;
 
+    volmode_needed = virStorageBackendZFSVolModeNeeded();
+    if (volmode_needed < 0)
+        goto cleanup;
     /**
      * $ zfs create -o volmode=dev -V 10240K test/volname
      *
@@ -281,8 +326,10 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
      *                   will lookup vfs.zfs.vol.mode sysctl value
      * -V -- tells to create a volume with the specified size
      */
-    cmd = virCommandNewArgList(ZFS, "create", "-o", "volmode=dev",
-                               "-V", NULL);
+    cmd = virCommandNewArgList(ZFS, "create", NULL);
+    if (volmode_needed)
+        virCommandAddArgList(cmd, "-o", "volmode=dev", NULL);
+    virCommandAddArg(cmd, "-V");
     virCommandAddArgFormat(cmd, "%lluK",
                            VIR_DIV_UP(vol->target.capacity, 1024));
     virCommandAddArgFormat(cmd, "%s/%s",
-- 
1.9.1