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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 <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: DHE <git@dehacked.net>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Christian Schwarz <me@cschwarz.com>
Closes #6102
This commit is contained in:
Christian Schwarz 2017-05-10 00:36:53 +02:00 committed by Brian Behlendorf
parent 78d95eaa73
commit 305bc4b370
4 changed files with 30 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/sys/fs/zfs.h
View File

@ -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 */

1
lib/libzfs/libzfs_dataset.c
View File

@ -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

24
man/man8/zfs.8
View File

@ -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

8
module/zcommon/zfs_prop.c
View File

@ -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,
"<count>", "SSCOUNT");
zprop_register_number(ZFS_PROP_GUID, "guid", 0, PROP_READONLY,
ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "<uint64>", "GUID");
zprop_register_number(ZFS_PROP_CREATETXG, "createtxg", 0, PROP_READONLY,
ZFS_TYPE_DATASET | ZFS_TYPE_BOOKMARK, "<uint64>", "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");