1 files changed, 146 insertions, 0 deletions
diff --git a/src/shared/loop-util.c b/src/shared/loop-util.c
new file mode 100644
index 0000000..bf426eb
--- /dev/null
+++ b/src/shared/loop-util.c
@@ -0,0 +1,146 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#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"
+#include "stat-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, r;
+
+        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,
+                        .relinquished = true, /* It's not allocated by us, don't destroy it when this object is freed */
+                };
+
+                *ret = d;
+                return d->fd;
+        }
+
+        r = stat_verify_regular(&st);
+        if (r < 0)
+                return r;
+
+        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 = TAKE_FD(loop),
+                .node = TAKE_PTR(loopdev),
+                .nr = nr,
+        };
+
+        *ret = d;
+        return d->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);
+        return mfree(d);
+}
+
+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;
+}