def write(self, data):
if not self._valid:
raise exception.VolumeDriverException(name=self._vdiname)
length = len(data)
cmd = ('dog', 'vdi', 'write', '-a', self._addr, '-p', self._port,
self._vdiname, self._offset, length)
self._execute(cmd, data)
self._offset += length
return length
def read(self, length=None):
if not self._valid:
raise exception.VolumeDriverException(name=self._vdiname)
cmd = ['dog', 'vdi', 'read', '-a', self._addr, '-p', self._port]
if self._snapshot_name:
cmd.extend(('-s', self._snapshot_name))
cmd.extend((self._vdiname, self._offset))
if length:
cmd.append(length)
data = self._execute(cmd)
self._offset += len(data)
return data
def _execute(self, cmd, data=None):
try:
# NOTE(yamada-h): processutils.execute causes busy waiting
# under eventlet.
# To avoid wasting CPU resources, it should not be used for
# the command which takes long time to execute.
# For workaround, we replace a subprocess module with
# the original one while only executing a read/write command.
_processutils_subprocess = processutils.subprocess
processutils.subprocess = eventlet.patcher.original('subprocess')
return processutils.execute(*cmd, process_input=data)[0]
except (processutils.ProcessExecutionError, OSError):
self._valid = False
raise exception.VolumeDriverException(name=self._vdiname)
finally:
processutils.subprocess = _processutils_subprocess
def seek(self, offset, whence=0):
if not self._valid:
raise exception.VolumeDriverException(name=self._vdiname)
if whence == 0:
# SEEK_SET or 0 - start of the stream (the default);
# offset should be zero or positive
new_offset = offset
elif whence == 1:
# SEEK_CUR or 1 - current stream position; offset may be negative
new_offset = self._offset + offset
else:
# SEEK_END or 2 - end of the stream; offset is usually negative
# TODO(yamada-h): Support SEEK_END
raise IOError(
_("Invalid argument - whence=%s not supported.") % whence)
if new_offset < 0:
raise IOError(_("Invalid argument - negative seek offset."))
self._offset = new_offset