libbtrfsutil: add btrfs_util_is_subvolume() and btrfs_util_subvolume_id()

These are the most trivial helpers in the library and will be used to
implement several of the more involved functions.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 125 insertions, 0 deletions

diff --git a/libbtrfsutil/subvolume.c b/libbtrfsutil/subvolume.c
new file mode 100644
index 00000000..7ae8142c
--- /dev/null
+++ b/libbtrfsutil/subvolume.c
@@ -0,0 +1,125 @@
+/*
+ * Copyright (C) 2018 Facebook
+ *
+ * This file is part of libbtrfsutil.
+ *
+ * libbtrfsutil 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * libbtrfsutil 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 libbtrfsutil.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
+
+#include "btrfsutil_internal.h"
+
+/*
+ * This intentionally duplicates btrfs_util_is_subvolume_fd() instead of opening
+ * a file descriptor and calling it, because fstat() and fstatfs() don't accept
+ * file descriptors opened with O_PATH on old kernels (before v3.6 and before
+ * v3.12, respectively), but stat() and statfs() can be called on a path that
+ * the user doesn't have read or write permissions to.
+ */
+PUBLIC enum btrfs_util_error btrfs_util_is_subvolume(const char *path)
+{
+	struct statfs sfs;
+	struct stat st;
+	int ret;
+
+	ret = statfs(path, &sfs);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_STATFS_FAILED;
+
+	if (sfs.f_type != BTRFS_SUPER_MAGIC) {
+		errno = EINVAL;
+		return BTRFS_UTIL_ERROR_NOT_BTRFS;
+	}
+
+	ret = stat(path, &st);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_STAT_FAILED;
+
+	if (st.st_ino != BTRFS_FIRST_FREE_OBJECTID || !S_ISDIR(st.st_mode)) {
+		errno = EINVAL;
+		return BTRFS_UTIL_ERROR_NOT_SUBVOLUME;
+	}
+
+	return BTRFS_UTIL_OK;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_is_subvolume_fd(int fd)
+{
+	struct statfs sfs;
+	struct stat st;
+	int ret;
+
+	ret = fstatfs(fd, &sfs);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_STATFS_FAILED;
+
+	if (sfs.f_type != BTRFS_SUPER_MAGIC) {
+		errno = EINVAL;
+		return BTRFS_UTIL_ERROR_NOT_BTRFS;
+	}
+
+	ret = fstat(fd, &st);
+	if (ret == -1)
+		return BTRFS_UTIL_ERROR_STAT_FAILED;
+
+	if (st.st_ino != BTRFS_FIRST_FREE_OBJECTID || !S_ISDIR(st.st_mode)) {
+		errno = EINVAL;
+		return BTRFS_UTIL_ERROR_NOT_SUBVOLUME;
+	}
+
+	return BTRFS_UTIL_OK;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_subvolume_id(const char *path,
+						     uint64_t *id_ret)
+{
+	enum btrfs_util_error err;
+	int fd;
+
+	fd = open(path, O_RDONLY);
+	if (fd == -1)
+		return BTRFS_UTIL_ERROR_OPEN_FAILED;
+
+	err = btrfs_util_subvolume_id_fd(fd, id_ret);
+	SAVE_ERRNO_AND_CLOSE(fd);
+	return err;
+}
+
+PUBLIC enum btrfs_util_error btrfs_util_subvolume_id_fd(int fd,
+							uint64_t *id_ret)
+{
+	struct btrfs_ioctl_ino_lookup_args args = {
+		.treeid = 0,
+		.objectid = BTRFS_FIRST_FREE_OBJECTID,
+	};
+	int ret;
+
+	ret = ioctl(fd, BTRFS_IOC_INO_LOOKUP, &args);
+	if (ret == -1) {
+		close(fd);
+		return BTRFS_UTIL_ERROR_INO_LOOKUP_FAILED;
+	}
+
+	*id_ret = args.treeid;
+
+	return BTRFS_UTIL_OK;
+}