[PATCH v2 RESEND 4/4] btrfs-progs: Add mount point output for 'btrfs fi df'

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Add mount point output for 'btrfs fi df'.
Also since the patch uses find_mount_root() to find mount point,
now 'btrfs fi df' can output more meaningful error message when given a
non-btrfs path.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
v2:
  Call realpath() before find_mount_root() to deal with relative path
---
 cmds-filesystem.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 0a9b62a..d76a1a5 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -187,12 +187,28 @@ static int cmd_filesystem_df(int argc, char **argv)
 	int ret;
 	int fd;
 	char *path;
+	char *real_path = NULL;
+	char *mount_point = NULL;
 	DIR *dirstream = NULL;
 
 	if (check_argc_exact(argc, 2))
 		usage(cmd_filesystem_df_usage);
 
 	path = argv[1];
+	real_path = realpath(path, NULL);
+	if (!real_path) {
+		fprintf(stderr, "ERROR: Failed to resolve real path for %s: %s\n",
+			path, strerror(errno));
+		return 1;
+	}
+	ret = find_mount_root(real_path, &mount_point);
+	if (ret < 0) {
+		free(real_path);
+		return 1;
+	}
+	printf("Mounted on: %s\n", mount_point);
+	free(real_path);
+	free(mount_point);
 
 	fd = open_file_or_dir(path, &dirstream);
 	if (fd < 0) {
-- 
2.0.1