Illumos 4929 - want prevsnap property

4929 want prevsnap property
Reviewed by: Adam Leventhal <adam.leventhal@delphix.com>
Reviewed by: Matt Amdur <matt.amdur@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: Boris Protopopov <bprotopopov@hotmail.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Dan McDonald <danmcd@omniti.com>

References:
  https://www.illumos.org/issues/4929
  illumos/illumos-gate@b461c74

Porting notes:
- [include/sys/fs/zfs.h]
  - f67d70 Create an 'overlay' property
  - 11b9ec Add full SELinux support
- [fs/zfs/dsl_dataset.c]
  - This increases the stack size of dsl_dataset_stats() but
    nothing has been changed until this is shown to be an issue.

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

Author: ahrens

include/sys/fs/zfs.h

@@ -155,6 +155,7 @@ typedef enum {
 	ZFS_PROP_RELATIME,
 	ZFS_PROP_REDUNDANT_METADATA,
 	ZFS_PROP_OVERLAY,
+	ZFS_PROP_PREV_SNAP,
 	ZFS_NUM_PROPS
 } zfs_prop_t;
 

module/zcommon/zfs_prop.c

@@ -452,6 +452,8 @@ zfs_prop_init(void)
 	    PROP_READONLY, ZFS_TYPE_DATASET, "OBJSETID");
 	zprop_register_hidden(ZFS_PROP_INCONSISTENT, "inconsistent",
 	    PROP_TYPE_NUMBER, PROP_READONLY, ZFS_TYPE_DATASET, "INCONSISTENT");
+	zprop_register_hidden(ZFS_PROP_PREV_SNAP, "prevsnap", PROP_TYPE_STRING,
+	    PROP_READONLY, ZFS_TYPE_FILESYSTEM | ZFS_TYPE_VOLUME, "PREVSNAP");
 
 	/*
 	 * Property to be removed once libbe is integrated

module/zfs/dsl_dataset.c

@@ -1695,6 +1695,12 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 		    dsl_dataset_phys(ds)->ds_unique_bytes);
 		get_clones_stat(ds, nv);
 	} else {
+		if (ds->ds_prev != NULL && ds->ds_prev != dp->dp_origin_snap) {
+			char buf[MAXNAMELEN];
+			dsl_dataset_name(ds->ds_prev, buf);
+			dsl_prop_nvlist_add_string(nv, ZFS_PROP_PREV_SNAP, buf);
+		}
+
 		dsl_dir_stats(ds->ds_dir, nv);
 	}