From 305bc4b370b20de81eaf10a1cf724374258b74d1 Mon Sep 17 00:00:00 2001 From: Christian Schwarz Date: Wed, 10 May 2017 00:36:53 +0200 Subject: [PATCH] Make createtxg and guid properties public Document the existence of `createtxg` and `guid` native properties in man pages and zfs command output. One of the great features of ZFS is incremental replication of snapshots, possibly between pools on different machines. Shell scripts are commonly used to auomate this procedure. They have to find the most recent common snapshot between both sides and then perform incremental send & recv. Currently, scripts rely on the sorting order of `zfs list`, which defaults to `createtxg`, and the assumption that snapshot names on either side do not change. By making `createtxg` and `guid` part of the public ZFS interface, scripts are enabled to use a) `createtxg` to determine the logical & temporal order of snapshots (the creation property is not an equivalent substitute since multiple snapshots may be created within one second) b) `guid` to uniquely identify a snapshot, independent of its current display name This has the potential of making scripts safer and correct. Reviewed-by: George Melikov Reviewed-by: Brian Behlendorf Reviewed-by: DHE Reviewed-by: Richard Laager Signed-off-by: Christian Schwarz Closes #6102 --- include/sys/fs/zfs.h | 2 +- lib/libzfs/libzfs_dataset.c | 1 + man/man8/zfs.8 | 24 ++++++++++++++++++++++++ module/zcommon/zfs_prop.c | 8 ++++---- 4 files changed, 30 insertions(+), 5 deletions(-) diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h index ba64876121..5b7bbb6898 100644 --- a/include/sys/fs/zfs.h +++ b/include/sys/fs/zfs.h @@ -113,7 +113,7 @@ typedef enum { ZFS_PROP_SNAPDIR, ZFS_PROP_PRIVATE, /* not exposed to user, temporary */ ZFS_PROP_ACLINHERIT, - ZFS_PROP_CREATETXG, /* not exposed to the user */ + ZFS_PROP_CREATETXG, ZFS_PROP_NAME, /* not exposed to the user */ ZFS_PROP_CANMOUNT, ZFS_PROP_ISCSIOPTIONS, /* not exposed to the user */ diff --git a/lib/libzfs/libzfs_dataset.c b/lib/libzfs/libzfs_dataset.c index 0f18fd6900..f1346b69c6 100644 --- a/lib/libzfs/libzfs_dataset.c +++ b/lib/libzfs/libzfs_dataset.c @@ -2695,6 +2695,7 @@ zfs_prop_get(zfs_handle_t *zhp, zfs_prop_t prop, char *propbuf, size_t proplen, break; case ZFS_PROP_GUID: + case ZFS_PROP_CREATETXG: /* * GUIDs are stored as numbers, but they are identifiers. * We don't want them to be pretty printed, because pretty diff --git a/man/man8/zfs.8 b/man/man8/zfs.8 index 6720796378..5d0b79b996 100644 --- a/man/man8/zfs.8 +++ b/man/man8/zfs.8 @@ -438,6 +438,18 @@ This property can also be referred to by its shortened column name, \fBavail\fR. For non-snapshots, the compression ratio achieved for the \fBused\fR space of this dataset, expressed as a multiplier. The \fBused\fR property includes descendant datasets, and, for clones, does not include the space shared with the origin snapshot. For snapshots, the \fBcompressratio\fR is the same as the \fBrefcompressratio\fR property. The \fBcompression\fR property controls whether compression is enabled on a dataset. .RE +.sp +.ne 2 +.na +\fB\fBcreatetxg\fR +.ad +.sp .6 +.RS 4n +The transaction group (TXG) in which the dataset was created. Bookmarks have the same \fBcreatetxg\fR as the snapshot they are initially tied to. +.sp +\fBcreatetxg\fR is suitable for ordering a list of snapshots, e.g. for incremental \fBsend\fR & \fBrecv\fR. +.RE + .sp .ne 2 .na @@ -485,6 +497,18 @@ dataset tree. This value is only available when a \fBfilesystem_limit\fR has been set somewhere in the tree under which the dataset resides. .RE +.sp +.ne 2 +.na +\fB\fBguid\fR +.ad +.sp .6 +.RS 4n +The 64 bit GUID of this dataset or bookmark, which does not change over its entire lifetime. +.sp +When a snapshot is sent to another pool, the received snapshot has the same GUID. Thus, \fBguid\fR is suitable to identify a snapshot across pools. +.RE + .sp .ne 2 .na diff --git a/module/zcommon/zfs_prop.c b/module/zcommon/zfs_prop.c index 82641b490c..97736ee278 100644 --- a/module/zcommon/zfs_prop.c +++ b/module/zcommon/zfs_prop.c @@ -439,6 +439,10 @@ zfs_prop_init(void) zprop_register_number(ZFS_PROP_SNAPSHOT_COUNT, "snapshot_count", UINT64_MAX, PROP_READONLY, ZFS_TYPE_FILESYSTEM | ZFS_TYPE_VOLUME, "", "SSCOUNT"); + zprop_register_number(ZFS_PROP_GUID, "guid", 0, PROP_READONLY, + ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "", "GUID"); + zprop_register_number(ZFS_PROP_CREATETXG, "createtxg", 0, PROP_READONLY, + ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "", "CREATETXG"); /* default number properties */ zprop_register_number(ZFS_PROP_QUOTA, "quota", 0, PROP_DEFAULT, @@ -466,8 +470,6 @@ zfs_prop_init(void) ZFS_TYPE_FILESYSTEM, "512 to 1M, power of 2", "RECSIZE"); /* hidden properties */ - zprop_register_hidden(ZFS_PROP_CREATETXG, "createtxg", PROP_TYPE_NUMBER, - PROP_READONLY, ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "CREATETXG"); zprop_register_hidden(ZFS_PROP_NUMCLONES, "numclones", PROP_TYPE_NUMBER, PROP_READONLY, ZFS_TYPE_SNAPSHOT, "NUMCLONES"); zprop_register_hidden(ZFS_PROP_NAME, "name", PROP_TYPE_STRING, @@ -477,8 +479,6 @@ zfs_prop_init(void) zprop_register_hidden(ZFS_PROP_STMF_SHAREINFO, "stmf_sbd_lu", PROP_TYPE_STRING, PROP_INHERIT, ZFS_TYPE_VOLUME, "STMF_SBD_LU"); - zprop_register_hidden(ZFS_PROP_GUID, "guid", PROP_TYPE_NUMBER, - PROP_READONLY, ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "GUID"); zprop_register_hidden(ZFS_PROP_USERACCOUNTING, "useraccounting", PROP_TYPE_NUMBER, PROP_READONLY, ZFS_TYPE_DATASET, "USERACCOUNTING");