btrfs: Show detail information when mount failed on missing devices

When mount failed because missing device, we can see following
dmesg:
 [ 1060.267743] BTRFS: too many missing devices, writeable mount is not allowed
 [ 1060.273158] BTRFS: open_ctree failed

This patch add missing_device_number and tolerated_missing_device_number
to above output, to let user know what really happened, and helps
bug-report and debug.

dmesg after patch:
 [  127.050367] BTRFS: missing devices(1) exceeds the limit(0), writeable mount is not allowed
 [  127.056099] BTRFS: open_ctree failed

Changelog v1->v2:
1: Changed to more clear description, suggested-by:
   Anand Jain <anand.jain@oracle.com>

Suggested-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f556c3732c2c16e22e0bcbd35f9ee1277179be5b..e49ae5ea904036de3e13cc429205f947980c30b2 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2950,8 +2950,9 @@ retry_root_backup:
        if (fs_info->fs_devices->missing_devices >
             fs_info->num_tolerated_disk_barrier_failures &&
            !(sb->s_flags & MS_RDONLY)) {
-               printk(KERN_WARNING "BTRFS: "
-                       "too many missing devices, writeable mount is not allowed\n");
+               pr_warn("BTRFS: missing devices(%llu) exceeds the limit(%d), writeable mount is not allowed\n",
+                       fs_info->fs_devices->missing_devices,
+                       fs_info->num_tolerated_disk_barrier_failures);
                goto fail_sysfs;
        }