terom@0: #!/usr/bin/python
terom@0: 
terom@0: import subprocess
terom@0: import os, os.path
terom@0: 
terom@0: import contextlib
terom@0: import logging
terom@0: 
terom@0: logging.basicConfig(
terom@0:     format  = '%(processName)s: %(name)s: %(levelname)s %(funcName)s : %(message)s',
terom@0:     level   = logging.DEBUG,
terom@0: )
terom@0: log = logging.getLogger()
terom@0: 
terom@0: LVM                 = '/sbin/lvm'
terom@0: LVM_VG              = 'asdf'
terom@0: LVM_SNAPSHOT_SIZE   = '5G'
terom@0: 
terom@0: def lvm_name (vg, lv) :
terom@0:     """
terom@0:         LVM vg/lv name.
terom@0:     """
terom@0: 
terom@0:     return '{vg}/{lv}'.format(vg=vg, lv=lv)
terom@0: 
terom@0: def lvm_path (vg, lv) :
terom@0:     """
terom@0:         Map LVM VG+LV to /dev path.
terom@0:     """
terom@0: 
terom@0:     return '/dev/{vg}/{lv}'.format(vg=vg, lv=lv)
terom@0: 
terom@0: def lvm_invoke (cmd, args) :
terom@0:     """
terom@0:         Invoke LVM command directly.
terom@0: 
terom@0:         Doesn't give any data on stdin, and keeps process stderr.
terom@0:         Returns stdout.
terom@0:     """
terom@0:     
terom@0:     log.debug("cmd={cmd}, args={args}".format(cmd=cmd, args=args))
terom@0: 
terom@0:     p = subprocess.Popen([LVM, cmd] + args, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
terom@0: 
terom@0:     # get output
terom@0:     stdout, stderr = p.communicate(input=None)
terom@0: 
terom@0:     if p.returncode :
terom@0:         raise Exception("LVM ({cmd}) failed: {returncode}".format(cmd=cmd, returncode=p.returncode))
terom@0: 
terom@0:     return stdout
terom@0: 
terom@0: def lvm (cmd, *args, **opts) :
terom@0:     """
terom@0:         Invoke simple LVM command with options/arguments, and no output.
terom@0:     """
terom@0: 
terom@0:     log.debug("cmd={cmd}, opts={opts}, args={args}".format(cmd=cmd, args=args, opts=opts))
terom@0: 
terom@0:     # process
terom@0:     opts = [('--{opt}'.format(opt=opt), value if value != True else None) for opt, value in opts.iteritems() if value]
terom@0: 
terom@0:     # flatten
terom@0:     opts = [str(opt_part) for opt_parts in opts for opt_part in opt_parts if opt_part]
terom@0: 
terom@0:     args = [str(arg) for arg in args if arg]
terom@0: 
terom@0:     # invoke
terom@0:     lvm_invoke(cmd, opts + args)
terom@0: 
terom@0: def lvm_snapshot_create (vg, lv, size=LVM_SNAPSHOT_SIZE) :
terom@0:     """
terom@0:         Create a new LVM snapshot of the given LV.
terom@0:         
terom@0:         Returns a (snapshot_name, dev_path) tuple.
terom@0:     """
terom@0: 
terom@0:     # path to device
terom@0:     lv_name = lvm_name(vg, lv)
terom@0:     lv_path = lvm_path(vg, lv)
terom@0: 
terom@0:     # snapshot name
terom@0:     snap_lv = '{lv}-backup'.format(lv=lv)
terom@0:     snap_name = lvm_name(vg, snap_lv)
terom@0:     snap_path = lvm_path(vg, snap_lv)
terom@0: 
terom@0:     # verify LV exists
terom@0:     lvm('lvs', lv_name)
terom@0:     
terom@0:     if not os.path.exists(lv_path) :
terom@0:         raise Exception("lvm_snapshot: source LV does not exist: {path}".format(path=lv_path))
terom@0: 
terom@0:     if os.path.exists(snap_path) :
terom@0:         raise Exception("lvm_snapshot: target LV snapshot already exists: {path}".format(path=snap_path))
terom@0: 
terom@0:     # create
terom@0:     lvm('lvcreate', lv_name, snapshot=True, name=snap_lv, size=size)
terom@0: 
terom@0:     # verify
terom@0:     if not os.path.exists(snap_path) :
terom@0:         raise Exception("lvm_snapshot: target LV snapshot did not appear: {path}".format(path=snap_path))
terom@0: 
terom@0:     # yay
terom@0:     return snap_name, snap_path
terom@0: 
terom@0: def lvm_snapshot_remove (name) :
terom@0:     """
terom@0:         Remove given snapshot volume.
terom@0:     """
terom@0: 
terom@0:     # XXX: can't deactivate snapshot volume
terom@0:     #lvm('lvchange', name, available='n')
terom@0: 
terom@0:     # XXX: risky!
terom@0:     lvm('lvremove', '-f', name)
terom@0: 
terom@0: @contextlib.contextmanager
terom@0: def lvm_snapshot (*args, **kwargs) :
terom@0:     """
terom@0:         A Context Manager for handling an LVM snapshot.
terom@0: 
terom@0:         with lvm_snapshot(vg, lv) as (snapshot_name, snapshot_path) : ...
terom@0:     """
terom@0: 
terom@0:     log.debug("creating snapshot: {0}".format(args))
terom@0:     name, path = lvm_snapshot_create(*args, **kwargs)
terom@0: 
terom@0:     log.debug("got name={0}, path={1}".format(name, path))
terom@0:     yield name, path
terom@0: 
terom@0:     log.debug("cleanup: {0}".format(name))
terom@0:     lvm_snapshot_remove(name)
terom@0: 
terom@0: def main (argv) :
terom@0:     # XXX: get LV from rsync command
terom@0:     lvm_vg='asdf'
terom@0:     backup_lv='test'
terom@0: 
terom@0:     # snapshot
terom@0:     log.info("Open snapshot...")
terom@0: 
terom@0:     with lvm_snapshot(lvm_vg, backup_lv) as (snapshot_name, snapshot_path):
terom@0:         log.info("Snapshot opened: {name}".format(name=snapshot_name))
terom@0: 
terom@0:         # ...
terom@0: 
terom@0: 
terom@0:         log.info("Done, cleaning up")
terom@0: 
terom@0:     return 1
terom@0: 
terom@0: if __name__ == '__main__' :
terom@0:     import sys
terom@0: 
terom@0:     sys.exit(main(sys.argv))
terom@0: