btrfs-progs: look up the containing tree root id

Find the tree id of the containing subvolume for a given file or
directory. For subvolume return it's own id.

$ btrfs inspect-internal rootid <path>

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/cmds-inspect.c b/cmds-inspect.c
index bdebf7d..f0c8e3d 100644 (file)
--- a/cmds-inspect.c
+++ b/cmds-inspect.c
@@ -301,6 +301,43 @@ out:
        return ret ? 1 : 0;
 }
 
+static const char* const cmd_rootid_usage[] = {
+       "btrfs inspect-internal rootid <path>",
+       "Get tree ID of the containing subvolume of path.",
+       NULL
+};
+
+static int cmd_rootid(int argc, char **argv)
+{
+       int ret;
+       int fd = -1;
+       u64 rootid;
+       DIR *dirstream = NULL;
+
+       if (check_argc_exact(argc, 2))
+               usage(cmd_rootid_usage);
+
+       fd = open_file_or_dir(argv[1], &dirstream);
+       if (fd < 0) {
+               fprintf(stderr, "ERROR: can't access '%s'\n", argv[1]);
+               ret = -ENOENT;
+               goto out;
+       }
+
+       ret = lookup_ino_rootid(fd, &rootid);
+       if (ret) {
+               fprintf(stderr, "%s: rootid failed with ret=%d\n",
+                       argv[0], ret);
+               goto out;
+       }
+
+       printf("%llu\n", (unsigned long long)rootid);
+out:
+       close_file_or_dir(fd, dirstream);
+
+       return !!ret;
+}
+
 const struct cmd_group inspect_cmd_group = {
        inspect_cmd_group_usage, NULL, {
                { "inode-resolve", cmd_inode_resolve, cmd_inode_resolve_usage,
@@ -309,6 +346,7 @@ const struct cmd_group inspect_cmd_group = {
                        cmd_logical_resolve_usage, NULL, 0 },
                { "subvolid-resolve", cmd_subvolid_resolve,
                        cmd_subvolid_resolve_usage, NULL, 0 },
+               { "rootid", cmd_rootid, cmd_rootid_usage, NULL, 0 },
                NULL_CMD_STRUCT
        }
 };

diff --git a/man/btrfs.8.in b/man/btrfs.8.in
index a2d4a8f..b94df2e 100644 (file)
--- a/man/btrfs.8.in
+++ b/man/btrfs.8.in
@@ -80,6 +80,8 @@ btrfs \- control a btrfs filesystem
 .PP
 \fBbtrfs\fP \fBinspect-internal subvolid-resolve\fP \fI<subvolid>\fP \fI<path>\fP
 .PP
+\fBbtrfs\fP \fBinspect-internal rootid\fP \fI<path>\fP
+.PP
 .PP
 \fBbtrfs\fP \fBsend\fP [-v] [-p \fI<parent>\fP] [-c \fI<clone-src>\fP] [-f \fI<outfile>\fP] \fI<subvol>\fP
 .PP
@@ -577,6 +579,13 @@ not enough to read all the resolved results. The max value one can set is 64k.
 Get file system paths for the given subvolume ID.
 .TP
 
+\fBinspect-internal rootid\fP \fI<path>\fP
+For a given file or directory, return the containing tree root id. For a
+subvolume return it's own tree id.
+
+The result is undefined for the so-called empty subvolumes (identified by inode number 2).
+.TP
+
 \fBsend\fP [-v] [-p \fI<parent>\fP] [-c \fI<clone-src>\fP] [-f \fI<outfile>\fP] \fI<subvol>\fP
 Send the subvolume to stdout.
 Sends the subvolume specified by \fI<subvol>\fR to stdout.

diff --git a/utils.c b/utils.c
index 86147f2..58d56f5 100644 (file)
--- a/utils.c
+++ b/utils.c
@@ -1975,3 +1975,33 @@ int ask_user(char *question)
               (answer = strtok_r(buf, " \t\n\r", &saveptr)) &&
               (!strcasecmp(answer, "yes") || !strcasecmp(answer, "y"));
 }
+
+/*
+ * For a given:
+ * - file or directory return the containing tree root id
+ * - subvolume return it's own tree id
+ * - BTRFS_EMPTY_SUBVOL_DIR_OBJECTID (directory with ino == 2) the result is
+ *   undefined and function returns -1
+ */
+int lookup_ino_rootid(int fd, u64 *rootid)
+{
+       struct btrfs_ioctl_ino_lookup_args args;
+       int ret;
+       int e;
+
+       memset(&args, 0, sizeof(args));
+       args.treeid = 0;
+       args.objectid = BTRFS_FIRST_FREE_OBJECTID;
+
+       ret = ioctl(fd, BTRFS_IOC_INO_LOOKUP, &args);
+       e = errno;
+       if (ret) {
+               fprintf(stderr, "ERROR: Failed to lookup root id - %s\n",
+                       strerror(e));
+               return ret;
+       }
+
+       *rootid = args.treeid;
+
+       return 0;
+}

diff --git a/utils.h b/utils.h
index fdef3f0..19f028f 100644 (file)
--- a/utils.h
+++ b/utils.h
@@ -81,4 +81,6 @@ int is_vol_small(char *file);
 int csum_tree_block(struct btrfs_root *root, struct extent_buffer *buf,
                           int verify);
 int ask_user(char *question);
+int lookup_ino_rootid(int fd, u64 *rootid);
+
 #endif