Fix generation of kernel uevents for snapshot rename on linux

`zvol_rename_minors()` needs to be given the full path not just the
snapshot name.  Use code removed in a0bd735 as a guide
to providing the necessary values.

Add ZTS check for /dev changes after snapshot rename.  After
renaming a snapshot with 'snapdev=visible' ensure that the /dev
entries are updated to reflect the rename.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: James Dingwall <james@dingwall.me.uk>
Closes #14223 
Closes #16600

module/zfs/dsl_dataset.c

@@ -2987,6 +2987,7 @@ dsl_dataset_rename_snapshot_sync_impl(dsl_pool_t *dp,
 	dsl_dataset_t *ds;
 	uint64_t val;
 	dmu_tx_t *tx = ddrsa->ddrsa_tx;
+	char *oldname, *newname;
 	int error;
 
 	error = dsl_dataset_snap_lookup(hds, ddrsa->ddrsa_oldsnapname, &val);
@@ -3011,8 +3012,14 @@ dsl_dataset_rename_snapshot_sync_impl(dsl_pool_t *dp,
 	VERIFY0(zap_add(dp->dp_meta_objset,
 	    dsl_dataset_phys(hds)->ds_snapnames_zapobj,
 	    ds->ds_snapname, 8, 1, &ds->ds_object, tx));
-	zvol_rename_minors(dp->dp_spa, ddrsa->ddrsa_oldsnapname,
-	    ddrsa->ddrsa_newsnapname, B_TRUE);
+
+	oldname = kmem_asprintf("%s@%s", ddrsa->ddrsa_fsname,
+	    ddrsa->ddrsa_oldsnapname);
+	newname = kmem_asprintf("%s@%s", ddrsa->ddrsa_fsname,
+	    ddrsa->ddrsa_newsnapname);
+	zvol_rename_minors(dp->dp_spa, oldname, newname, B_TRUE);
+	kmem_strfree(oldname);
+	kmem_strfree(newname);
 
 	dsl_dataset_rele(ds, FTAG);
 	return (0);

tests/zfs-tests/tests/functional/zvol/zvol_misc/zvol_misc_snapdev.ksh

@@ -117,5 +117,18 @@ log_must zfs set snapdev=visible $TESTPOOL
 verify_inherited 'snapdev' 'hidden' $SUBZVOL $VOLFS
 blockdev_missing $SUBSNAPDEV
 blockdev_exists $SNAPDEV
+log_must zfs destroy $SNAP
+
+# 4. Verify "rename" is correctly reflected when "snapdev=visible"
+# 4.1 First create a snapshot and verify the device is present
+log_must zfs snapshot $SNAP
+log_must zfs set snapdev=visible $ZVOL
+blockdev_exists $SNAPDEV
+# 4.2 rename the snapshot and verify the devices are updated
+log_must zfs rename $SNAP $SNAP-new
+blockdev_missing $SNAPDEV
+blockdev_exists $SNAPDEV-new
+# 4.3 cleanup
+log_must zfs destroy $SNAP-new
 
 log_pass "ZFS volume property 'snapdev' works as expected"