From 94789777b9e8f350ba815b07baa5383e99cd1944 Mon Sep 17 00:00:00 2001
From: Anand Jain <anand.jain@oracle.com>
Date: Tue, 15 Sep 2015 16:46:22 +0800
Subject: [PATCH] btrfs-progs: provide fail safe for BTRFS_IOC_GET_FSLABEL
 ioctl

Old kernels before 3.9 do not provide ioctl BTRFS_IOC_GET_FSLABEL.
So we need to provide a fail safe logic for btrfs-progs running
on those kernel.

In this patch when get_label_mounted() fails on the old kernel
it will fail back to the old method and uses get_label_unmounted(),
where it will read from the disk directly.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 cmds-filesystem.c |  8 +++++++-
 utils.c           | 18 +++++++++---------
 utils.h           |  1 +
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 8822695e..09cb37d9 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -468,7 +468,13 @@ static int btrfs_scan_kernel(void *search, unsigned unit_mode)
 			goto out;
 		}
 
-		if (get_label_mounted(mnt->mnt_dir, label)) {
+		ret = get_label_mounted(mnt->mnt_dir, label);
+		/* provide backward kernel compatibility */
+		if (ret == -ENOTTY)
+			ret = get_label_unmounted(
+				(const char *)dev_info_arg->path, label);
+
+		if (ret) {
 			kfree(dev_info_arg);
 			goto out;
 		}
diff --git a/utils.c b/utils.c
index 679be3cd..bb4091ec 100644
--- a/utils.c
+++ b/utils.c
@@ -1740,7 +1740,7 @@ static int set_label_mounted(const char *mount_path, const char *label)
 	return 0;
 }
 
-static int get_label_unmounted(const char *dev, char *label)
+int get_label_unmounted(const char *dev, char *label)
 {
 	struct btrfs_root *root;
 	int ret;
@@ -1750,11 +1750,6 @@ static int get_label_unmounted(const char *dev, char *label)
 	       fprintf(stderr, "FATAL: error checking %s mount status\n", dev);
 	       return -1;
 	}
-	if (ret > 0) {
-		fprintf(stderr, "ERROR: dev %s is mounted, use mount point\n",
-			dev);
-		return -1;
-	}
 
 	/* Open the super_block at the default location
 	 * and as read-only.
@@ -1779,6 +1774,7 @@ int get_label_mounted(const char *mount_path, char *labelp)
 {
 	char label[BTRFS_LABEL_SIZE];
 	int fd;
+	int ret;
 
 	fd = open(mount_path, O_RDONLY | O_NOATIME);
 	if (fd < 0) {
@@ -1787,10 +1783,14 @@ int get_label_mounted(const char *mount_path, char *labelp)
 	}
 
 	memset(label, '\0', sizeof(label));
-	if (ioctl(fd, BTRFS_IOC_GET_FSLABEL, label) < 0) {
-		fprintf(stderr, "ERROR: unable get label %s\n", strerror(errno));
+	ret = ioctl(fd, BTRFS_IOC_GET_FSLABEL, label);
+	if (ret < 0) {
+		if (errno != ENOTTY)
+			fprintf(stderr, "ERROR: unable to get label %s\n",
+					strerror(errno));
+		ret = -errno;
 		close(fd);
-		return -1;
+		return ret;
 	}
 
 	strncpy(labelp, label, sizeof(label));
diff --git a/utils.h b/utils.h
index dce0a47c..93e1de6b 100644
--- a/utils.h
+++ b/utils.h
@@ -164,6 +164,7 @@ u64 btrfs_device_size(int fd, struct stat *st);
 #define strncpy_null(dest, src) __strncpy__null(dest, src, sizeof(dest))
 int test_dev_for_mkfs(char *file, int force_overwrite);
 int get_label_mounted(const char *mount_path, char *labelp);
+int get_label_unmounted(const char *dev, char *label);
 int test_num_disk_vs_raid(u64 metadata_profile, u64 data_profile,
 	u64 dev_cnt, int mixed);
 int group_profile_max_safe_loss(u64 flags);