LU-8900 snapshot: user space snapshot tools

LU-8900 snapshot: user space snapshot tools

The user space snapshot tools are implemented as part of the
lctl tools set. They use other user-space tools, such as lctl
commands for write barrier on all MDTs, fork/erase Lustre
configuration, zfs/zpool commands for backend zfs snapshot.

1. Create the snapshot
lctl snapshot_create [-b | --barrier [on | off]]
[-c | --comment comment] <-F | --fsname fsname> [-h | --help]
<-n | --name ssname> [-r | --rsh remote_shell]
[-t | --timeout timeout]

2. Destroy the snapshot
lctl snapshot_destroy [-f | --force] <-F | --fsname fsname>
[-h | --help] <-n | --name ssname> [-r | --rsh remote_shell]

3. Modify the snapshot
lctl snapshot_modify [-c | --comment comment]
<-F | --fsname fsname> [-h | --help] <-n | --name ssname>
[-N | --new new_ssname] [-r | --rsh remote_shell]

4. Query the snapshot(s)
lctl snapshot_list [-d | --detail] <-F | --fsname fsname>
[-h | --help] [-n | --name ssname] [-r | --rsh remote_shell]

5. Mount the snapshot
lctl snapshot_mount <-F | --fsname fsname> [-h | --help]
<-n | --name ssname> [-r | --rsh remote_shell]

6. Umount the snapshot
lctl snapshot_umount <-F | --fsname fsname> [-h | --help]
<-n | --name ssname> [-r | --rsh remote_shell]

The system config information, such as each target's hostname,
pool name, local filesystem name, role, index, and so on, will
be written in the snapshot config file "/etc/ldev.conf". To be
compatible with old snapshot usage, it will firstly check whether
the "/etc/ldev.conf" exists or not, it yes, it will load the
configuration from such file preferentially, otherwise, the file
"/etc/lsnapshot/${fsname}.conf" will be used.

Test-Parameters: alwaysuploadlogs envdefinitions=SLOW=yes mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs mdscount=2 mdtcount=4 testlist=sanity-lsnapshot
Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I1191c2ea35c355e8554bd2bd022c1b9d32741392
Reviewed-on: https://review.whamcloud.com/24269
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>