[RFC PATCH 1/2] btrfs: Add missing device check in dev_info/rm_dev ioctl

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

Old btrfs can't find a missing btrfs device since there is no
mechanism for block layer to inform fs layer.

But we can use a workaround that only check status(by using
request_queue->queue_flags) of every device in a btrfs
filesystem when calling dev_info/rm_dev ioctl, since other ioctls
do not really cares about missing device.

Cc: Anand Jain <Anand.Jain@oracle.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
 fs/btrfs/ioctl.c   |  1 +
 fs/btrfs/volumes.c | 25 ++++++++++++++++++++++++-
 fs/btrfs/volumes.h |  2 ++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0401397..7680a40 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2606,6 +2606,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
 		goto out;
 	}
 
+	btrfs_check_dev_missing(root, dev, 1);
 	di_args->devid = dev->devid;
 	di_args->bytes_used = dev->bytes_used;
 	di_args->total_bytes = dev->total_bytes;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d241130a..c7d7908 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1548,9 +1548,10 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		 * is held.
 		 */
 		list_for_each_entry(tmp, devices, dev_list) {
+			btrfs_check_dev_missing(root, tmp, 0);
 			if (tmp->in_fs_metadata &&
 			    !tmp->is_tgtdev_for_dev_replace &&
-			    !tmp->bdev) {
+			    (!tmp->bdev || tmp->missing)) {
 				device = tmp;
 				break;
 			}
@@ -6300,3 +6301,25 @@ int btrfs_scratch_superblock(struct btrfs_device *device)
 
 	return 0;
 }
+
+/* If need_lock is set, uuid_mutex will be used */
+int btrfs_check_dev_missing(struct btrfs_root *root, struct btrfs_device *dev,
+			    int need_lock)
+{
+	struct request_queue *q;
+
+	if (unlikely(!dev || !dev->bdev || !dev->bdev->bd_queue))
+		return -ENOENT;
+	q = dev->bdev->bd_queue;
+
+	if (need_lock)
+		mutex_lock(&uuid_mutex);
+	if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags) ||
+	    test_bit(QUEUE_FLAG_DYING, &q->queue_flags)) {
+		dev->missing = 1;
+		root->fs_info->fs_devices->missing_devices++;
+	}
+	if (need_lock)
+		mutex_unlock(&uuid_mutex);
+	return 0;
+}
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 80754f9..47a44af 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -356,6 +356,8 @@ unsigned long btrfs_full_stripe_len(struct btrfs_root *root,
 int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 				struct btrfs_root *extent_root,
 				u64 chunk_offset, u64 chunk_size);
+int btrfs_check_dev_missing(struct btrfs_root *root, struct btrfs_device *dev,
+			    int need_lock);
 static inline void btrfs_dev_stat_inc(struct btrfs_device *dev,
 				      int index)
 {
-- 
1.9.2