btrfs-util: Move subvolume creation to basic/btrfs.h

Also make btrfs_subvol_make() an openat style function.

src/basic/btrfs.c

@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <linux/btrfs.h>
+#include <sys/ioctl.h>
+
+#include "btrfs.h"
+#include "fd-util.h"
+#include "fs-util.h"
+#include "path-util.h"
+
+int btrfs_validate_subvolume_name(const char *name) {
+
+        if (!filename_is_valid(name))
+                return -EINVAL;
+
+        if (strlen(name) > BTRFS_SUBVOL_NAME_MAX)
+                return -E2BIG;
+
+        return 0;
+}
+
+static int extract_subvolume_name(const char *path, char **ret) {
+        _cleanup_free_ char *fn = NULL;
+        int r;
+
+        assert(path);
+        assert(ret);
+
+        r = path_extract_filename(path, &fn);
+        if (r < 0)
+                return r;
+
+        r = btrfs_validate_subvolume_name(fn);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(fn);
+        return 0;
+}
+
+int btrfs_subvol_make(int dir_fd, const char *path) {
+        struct btrfs_ioctl_vol_args args = {};
+        _cleanup_free_ char *subvolume = NULL;
+        _cleanup_close_ int fd = -EBADF;
+        int r;
+
+        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(!isempty(path));
+
+        r = extract_subvolume_name(path, &subvolume);
+        if (r < 0)
+                return r;
+
+        r = path_extract_directory(path, NULL);
+        if (r >= 0) {
+                fd = open_parent_at(dir_fd, path, O_RDONLY|O_CLOEXEC|O_CLOEXEC, 0);
+                if (fd < 0)
+                        return fd;
+
+                dir_fd = fd;
+        }
+
+        strncpy(args.name, subvolume, sizeof(args.name)-1);
+
+        return RET_NERRNO(ioctl(dir_fd, BTRFS_IOC_SUBVOL_CREATE, &args));
+}
+
+int btrfs_subvol_make_fallback(int dir_fd, const char *path, mode_t mode) {
+        mode_t old, combined;
+        int r;
+
+        assert(path);
+
+        /* Let's work like mkdir(), i.e. take the specified mode, and mask it with the current umask. */
+        old = umask(~mode);
+        combined = old | ~mode;
+        if (combined != ~mode)
+                umask(combined);
+        r = btrfs_subvol_make(dir_fd, path);
+        umask(old);
+
+        if (r >= 0)
+                return 1; /* subvol worked */
+        if (r != -ENOTTY)
+                return r;
+
+        if (mkdirat(dir_fd, path, mode) < 0)
+                return -errno;
+
+        return 0; /* plain directory */
+}

src/basic/btrfs.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <fcntl.h>
+
+int btrfs_validate_subvolume_name(const char *name);
+
+int btrfs_subvol_make(int dir_fd, const char *path);
+
+int btrfs_subvol_make_fallback(int dir_fd, const char *path, mode_t mode);

src/basic/meson.build

@@ -8,6 +8,7 @@ basic_sources = files(
         'argv-util.c',
         'arphrd-util.c',
         'audit-util.c',
+        'btrfs.c',
         'build.c',
         'bus-label.c',
         'cap-list.c',