7600 zfs rollback should pass target snapshot to kernel

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>

usr/src/lib/libzfs/common/libzfs_dataset.c

@@ -3996,14 +3996,19 @@ zfs_rollback(zfs_handle_t *zhp, zfs_handle_t *snap, boolean_t force)
 	}
 
 	/*
-	 * We rely on zfs_iter_children() to verify that there are no
-	 * newer snapshots for the given dataset.  Therefore, we can
-	 * simply pass the name on to the ioctl() call.  There is still
-	 * an unlikely race condition where the user has taken a
-	 * snapshot since we verified that this was the most recent.
+	 * Pass both the filesystem and the wanted snapshot names,
+	 * we would get an error back if the snapshot is destroyed or
+	 * a new snapshot is created before this request is processed.
 	 */
-	err = lzc_rollback(zhp->zfs_name, NULL, 0);
-	if (err != 0) {
+	err = lzc_rollback_to(zhp->zfs_name, snap->zfs_name);
+	if (err == EXDEV) {
+		zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
+		    "'%s' is not the latest snapshot"), snap->zfs_name);
+		(void) zfs_error_fmt(zhp->zfs_hdl, EZFS_BUSY,
+		    dgettext(TEXT_DOMAIN, "cannot rollback '%s'"),
+		    zhp->zfs_name);
+		return (err);
+	} else if (err != 0) {
 		(void) zfs_standard_error_fmt(zhp->zfs_hdl, errno,
 		    dgettext(TEXT_DOMAIN, "cannot rollback '%s'"),
 		    zhp->zfs_name);

usr/src/lib/libzfs_core/common/libzfs_core.c

@@ -736,6 +736,9 @@ lzc_receive_with_header(const char *snapname, nvlist_t *props,
  * Roll back this filesystem or volume to its most recent snapshot.
  * If snapnamebuf is not NULL, it will be filled in with the name
  * of the most recent snapshot.
+ * Note that the latest snapshot may change if a new one is concurrently
+ * created or the current one is destroyed.  lzc_rollback_to can be used
+ * to roll back to a specific latest snapshot.
  *
  * Return 0 on success or an errno on failure.
  */
@@ -758,6 +761,27 @@ lzc_rollback(const char *fsname, char *snapnamebuf, int snapnamelen)
 	return (err);
 }
 
+/*
+ * Roll back this filesystem or volume to the specified snapshot,
+ * if possible.
+ *
+ * Return 0 on success or an errno on failure.
+ */
+int
+lzc_rollback_to(const char *fsname, const char *snapname)
+{
+	nvlist_t *args;
+	nvlist_t *result;
+	int err;
+
+	args = fnvlist_alloc();
+	fnvlist_add_string(args, "target", snapname);
+	err = lzc_ioctl(ZFS_IOC_ROLLBACK, fsname, args, &result);
+	nvlist_free(args);
+	nvlist_free(result);
+	return (err);
+}
+
 /*
  * Creates bookmarks.
  *

usr/src/lib/libzfs_core/common/libzfs_core.h

@@ -84,6 +84,7 @@ int lzc_receive_with_header(const char *, nvlist_t *, const char *, boolean_t,
 boolean_t lzc_exists(const char *);
 
 int lzc_rollback(const char *, char *, int);
+int lzc_rollback_to(const char *, const char *);
 
 int lzc_channel_program(const char *, const char *, uint64_t, uint64_t,
     nvlist_t *, nvlist_t **);

usr/src/lib/libzfs_core/common/mapfile-vers

@@ -58,6 +58,7 @@ SYMBOL_VERSION ILLUMOS_0.1 {
 	lzc_receive_with_header;
 	lzc_release;
 	lzc_rollback;
+	lzc_rollback_to;
 	lzc_send;
 	lzc_send_resume;
 	lzc_send_space;

usr/src/uts/common/fs/zfs/dsl_dataset.c

@@ -2454,6 +2454,7 @@ dsl_dataset_handoff_check(dsl_dataset_t *ds, void *owner, dmu_tx_t *tx)
 
 typedef struct dsl_dataset_rollback_arg {
 	const char *ddra_fsname;
+	const char *ddra_tosnap;
 	void *ddra_owner;
 	nvlist_t *ddra_result;
 } dsl_dataset_rollback_arg_t;
@@ -2495,6 +2496,18 @@ dsl_dataset_rollback_check(void *arg, dmu_tx_t *tx)
 		return (SET_ERROR(EAGAIN));
 	}
 
+	/*
+	 * If the expected target snapshot is specified, then check that
+	 * the latest snapshot is it.
+	 */
+	if (ddra->ddra_tosnap != NULL) {
+		char namebuf[ZFS_MAX_DATASET_NAME_LEN];
+
+		dsl_dataset_name(ds->ds_prev, namebuf);
+		if (strcmp(namebuf, ddra->ddra_tosnap) != 0)
+			return (SET_ERROR(EXDEV));
+	}
+
 	/* must not have any bookmarks after the most recent snapshot */
 	nvlist_t *proprequest = fnvlist_alloc();
 	fnvlist_add_boolean(proprequest, zfs_prop_to_name(ZFS_PROP_CREATETXG));
@@ -2596,11 +2609,13 @@ dsl_dataset_rollback_sync(void *arg, dmu_tx_t *tx)
  * notes above zfs_suspend_fs() for further details.
  */
 int
-dsl_dataset_rollback(const char *fsname, void *owner, nvlist_t *result)
+dsl_dataset_rollback(const char *fsname, const char *tosnap, void *owner,
+    nvlist_t *result)
 {
 	dsl_dataset_rollback_arg_t ddra;
 
 	ddra.ddra_fsname = fsname;
+	ddra.ddra_tosnap = tosnap;
 	ddra.ddra_owner = owner;
 	ddra.ddra_result = result;
 

usr/src/uts/common/fs/zfs/sys/dsl_dataset.h

@@ -375,7 +375,8 @@ void dsl_dataset_set_refreservation_sync_impl(dsl_dataset_t *ds,
 void dsl_dataset_zapify(dsl_dataset_t *ds, dmu_tx_t *tx);
 boolean_t dsl_dataset_is_zapified(dsl_dataset_t *ds);
 boolean_t dsl_dataset_has_resume_receive_state(dsl_dataset_t *ds);
-int dsl_dataset_rollback(const char *fsname, void *owner, nvlist_t *result);
+int dsl_dataset_rollback(const char *fsname, const char *tosnap, void *owner,
+    nvlist_t *result);
 
 void dsl_dataset_deactivate_feature(uint64_t dsobj,
     spa_feature_t f, dmu_tx_t *tx);

usr/src/uts/common/fs/zfs/zfs_ioctl.c

@@ -3678,18 +3678,29 @@ zfs_ioc_destroy(zfs_cmd_t *zc)
 /*
  * fsname is name of dataset to rollback (to most recent snapshot)
  *
- * innvl is not used.
+ * innvl may contain name of expected target snapshot
  *
  * outnvl: "target" -> name of most recent snapshot
  * }
  */
 /* ARGSUSED */
 static int
-zfs_ioc_rollback(const char *fsname, nvlist_t *args, nvlist_t *outnvl)
+zfs_ioc_rollback(const char *fsname, nvlist_t *innvl, nvlist_t *outnvl)
 {
 	zfsvfs_t *zfsvfs;
+	char *target = NULL;
 	int error;
 
+	(void) nvlist_lookup_string(innvl, "target", &target);
+	if (target != NULL) {
+		int fslen = strlen(fsname);
+
+		if (strncmp(fsname, target, fslen) != 0)
+			return (SET_ERROR(EINVAL));
+		if (target[fslen] != '@')
+			return (SET_ERROR(EINVAL));
+	}
+
 	if (getzfsvfs(fsname, &zfsvfs) == 0) {
 		dsl_dataset_t *ds;
 
@@ -3698,13 +3709,14 @@ zfs_ioc_rollback(const char *fsname, nvlist_t *args, nvlist_t *outnvl)
 		if (error == 0) {
 			int resume_err;
 
-			error = dsl_dataset_rollback(fsname, zfsvfs, outnvl);
+			error = dsl_dataset_rollback(fsname, target, zfsvfs,
+			    outnvl);
 			resume_err = zfs_resume_fs(zfsvfs, ds);
 			error = error ? error : resume_err;
 		}
 		VFS_RELE(zfsvfs->z_vfs);
 	} else {
-		error = dsl_dataset_rollback(fsname, NULL, outnvl);
+		error = dsl_dataset_rollback(fsname, target, NULL, outnvl);
 	}
 	return (error);
 }