[PATCH v3 1/2] btrfs: fix device order consistency

[Anand Jain <anand.jain@oracle.com>]

By maintaining the device order consistency it makes reproducing
the problems related to missing chunk in the degraded mode much more
consistent. So fix this by sorting the devices by devid within the
kernel. So that we know which device is assigned to the struct
fs_info::latest_bdev when all the devices are having and same
SB generation.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/volumes.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b5036bd69e6a..0109f370ad5b 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -27,6 +27,7 @@
 #include <linux/raid/pq.h>
 #include <linux/semaphore.h>
 #include <linux/uuid.h>
+#include <linux/list_sort.h>
 #include <asm/div64.h>
 #include "ctree.h"
 #include "extent_map.h"
@@ -1102,6 +1103,20 @@ static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	return ret;
 }
 
+static int device_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct btrfs_device *dev1, *dev2;
+
+	dev1 = list_entry(a, struct btrfs_device, dev_list);
+	dev2 = list_entry(b, struct btrfs_device, dev_list);
+
+	if (dev1->devid < dev2->devid)
+		return -1;
+	else if (dev1->devid > dev2->devid)
+		return 1;
+	return 0;
+}
+
 int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder)
 {
@@ -1112,6 +1127,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		fs_devices->opened++;
 		ret = 0;
 	} else {
+		list_sort(NULL, &fs_devices->devices, device_cmp);
 		ret = __btrfs_open_devices(fs_devices, flags, holder);
 	}
 	mutex_unlock(&uuid_mutex);
-- 
2.7.0