# Copyright 2011 Red Hat, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Support for mounting images with qemu-nbd."""

import os
import random
import re

try:
    from oslo_config import cfg
except BaseException:
    from oslo.config import cfg

try:
    from oslo_log import log as logging
except BaseException:
    from nova.openstack.common import log as logging

from nova import utils
from nova.virt.disk.mount import api

LOG = logging.getLogger(__name__)

nbd_opts = [
    cfg.IntOpt(
        "timeout_nbd",
        default=10,
        help="Amount of time, in seconds, to wait for NBD device start up.",
    )
]

CONF = cfg.CONF
CONF.register_opts(nbd_opts)

NBD_DEVICE_RE = re.compile("nbd[0-9]+")


class NbdMount(api.Mount):
    """qemu-nbd support disk images."""

    mode = "nbd"

    def _detect_nbd_devices(self):
        """Detect nbd device files."""
        return list(filter(NBD_DEVICE_RE.match, os.listdir("/sys/block/")))

    def _find_unused(self, devices):
        for device in devices:
            if not os.path.exists(os.path.join("/sys/block/", device, "pid")):
                if not os.path.exists("/var/lock/qemu-nbd-%s" % device):
                    return device
                else:
                    LOG.error(
                        "NBD error - previous umount did not "
                        "cleanup /var/lock/qemu-nbd-%s.",
                        device,
                    )
        LOG.warning("No free nbd devices")
        return None

    def _allocate_nbd(self):
        if not os.path.exists("/sys/block/nbd0"):
            LOG.error("nbd module not loaded")
            self.error = "nbd unavailable: module not loaded"
            return None

        devices = self._detect_nbd_devices()
        random.shuffle(devices)
        device = self._find_unused(devices)
        if not device:
            # really want to log this info, not raise
            self.error = "No free nbd devices"
            return None
        return os.path.join("/dev", device)

    @utils.synchronized("nbd-allocation-lock")
    def _inner_get_dev(self):
        device = self._allocate_nbd()
        if not device:
            return False

        # NOTE(mikal): qemu-nbd will return an error if the device file is
        # already in use.
        LOG.debug(
            "Get nbd device %(dev)s for %(imgfile)s",
            {"dev": device, "imgfile": self.image},
        )
        _out, err = utils.trycmd(
            "qemu-nbd",
            "-c",
            device,
            self.image,
            "--aio=native",
            "--nocache",
            run_as_root=True,
        )
        if err:
            self.error = "qemu-nbd error: %s" % err
            LOG.info("NBD mount error: %s", self.error)
            _out, err = utils.trycmd("qemu-nbd", "-d", device, run_as_root=True)
            if err:
                LOG.warning(
                    "Detaching from erroneous nbd device returned error: %s", err,
                )
            return False

        # NOTE(vish): this forks into another process, so give it a chance
        # to set up before continuing
        pidfile = "/sys/block/%s/pid" % os.path.basename(device)
        for _i in range(CONF.timeout_nbd):
            if os.path.exists(pidfile):
                self.device = device
                break
            else:
                self.error = "nbd device %s did not show up" % device
                LOG.info("NBD mount error: %s", self.error)

                # Cleanup
                _out, err = utils.trycmd("qemu-nbd", "-d", device, run_as_root=True)
                if err:
                    LOG.warning(
                        "Detaching from erroneous nbd device returned error: %s",
                        err,
                    )
                return False

        self.error = ""
        self.linked = True
        return True

    def get_dev(self):
        """Retry requests for NBD devices."""
        return self._get_dev_retry_helper()

    def unget_dev(self):
        if not self.linked:
            return
        LOG.debug("Release nbd device %s", self.device)
        utils.execute("qemu-nbd", "-d", self.device, run_as_root=True)
        self.linked = False
        self.device = None

    def flush_dev(self):
        """flush NBD block device buffer."""
        # Perform an explicit BLKFLSBUF to support older qemu-nbd(s).
        # Without this flush, when a nbd device gets re-used the
        # qemu-nbd intermittently hangs.
        if self.device:
            utils.execute("blockdev", "--flushbufs", self.device, run_as_root=True)