src/shared/loop-util.c

/***
  This file is part of systemd.

  Copyright 2016 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <fcntl.h>
#include <linux/loop.h>
#include <sys/ioctl.h>
#include <sys/stat.h>

#include "alloc-util.h"
#include "fd-util.h"
#include "loop-util.h"

int loop_device_make(int fd, int open_flags, LoopDevice **ret) {
        const struct loop_info64 info = {
                .lo_flags = LO_FLAGS_AUTOCLEAR|LO_FLAGS_PARTSCAN|(open_flags == O_RDONLY ? LO_FLAGS_READ_ONLY : 0),
        };

        _cleanup_close_ int control = -1, loop = -1;
        _cleanup_free_ char *loopdev = NULL;
        struct stat st;
        LoopDevice *d;
        int nr;

        assert(fd >= 0);
        assert(ret);
        assert(IN_SET(open_flags, O_RDWR, O_RDONLY));

        if (fstat(fd, &st) < 0)
                return -errno;

        if (S_ISBLK(st.st_mode)) {
                int copy;

                /* If this is already a block device, store a copy of the fd as it is */

                copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
                if (copy < 0)
                        return -errno;

                d = new0(LoopDevice, 1);
                if (!d)
                        return -ENOMEM;

                *d = (LoopDevice) {
                        .fd = copy,
                        .nr = -1,
                };

                *ret = d;

                return 0;
        }

        if (!S_ISREG(st.st_mode))
                return -EINVAL;

        control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
        if (control < 0)
                return -errno;

        nr = ioctl(control, LOOP_CTL_GET_FREE);
        if (nr < 0)
                return -errno;

        if (asprintf(&loopdev, "/dev/loop%i", nr) < 0)
                return -ENOMEM;

        loop = open(loopdev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
        if (loop < 0)
                return -errno;

        if (ioctl(loop, LOOP_SET_FD, fd) < 0)
                return -errno;

        if (ioctl(loop, LOOP_SET_STATUS64, &info) < 0)
                return -errno;

        d = new(LoopDevice, 1);
        if (!d)
                return -ENOMEM;

        *d = (LoopDevice) {
                .fd = loop,
                .node = loopdev,
                .nr = nr,
        };

        loop = -1;
        loopdev = NULL;

        *ret = d;

        return (*ret)->fd;
}

int loop_device_make_by_path(const char *path, int open_flags, LoopDevice **ret) {
        _cleanup_close_ int fd = -1;

        assert(path);
        assert(ret);
        assert(IN_SET(open_flags, O_RDWR, O_RDONLY));

        fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
        if (fd < 0)
                return -errno;

        return loop_device_make(fd, open_flags, ret);
}

LoopDevice* loop_device_unref(LoopDevice *d) {
        if (!d)
                return NULL;

        if (d->fd >= 0) {

                if (d->nr >= 0 && !d->relinquished) {
                        if (ioctl(d->fd, LOOP_CLR_FD) < 0)
                                log_debug_errno(errno, "Failed to clear loop device: %m");

                }

                safe_close(d->fd);
        }

        if (d->nr >= 0 && !d->relinquished) {
                _cleanup_close_ int control = -1;

                control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
                if (control < 0)
                        log_debug_errno(errno, "Failed to open loop control device: %m");
                else {
                        if (ioctl(control, LOOP_CTL_REMOVE, d->nr) < 0)
                                log_debug_errno(errno, "Failed to remove loop device: %m");
                }
        }

        free(d->node);
        free(d);

        return NULL;
}

void loop_device_relinquish(LoopDevice *d) {
        assert(d);

        /* Don't attempt to clean up the loop device anymore from this point on. Leave the clean-ing up to the kernel
         * itself, using the loop device "auto-clear" logic we already turned on when creating the device. */

        d->relinquished = true;
}