Fix btrfs_open_devices to deal with changes since the scan ioctls

Devices can change after the scan ioctls are done, and btrfs_open_devices
needs to be able to verify them as they are opened and used by the FS.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

3 files changed, 63 insertions, 15 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 38b0d9ecda6a..264f297260f8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1266,10 +1266,10 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 
         btrfs_parse_options(options, tree_root, NULL);
 
-        if (btrfs_super_num_devices(disk_super) > fs_devices->num_devices) {
+        if (btrfs_super_num_devices(disk_super) > fs_devices->open_devices) {
                 printk("Btrfs: wanted %llu devices, but found %llu\n",
                        (unsigned long long)btrfs_super_num_devices(disk_super),
-                       (unsigned long long)fs_devices->num_devices);
+                       (unsigned long long)fs_devices->open_devices);
                 if (btrfs_test_opt(tree_root, DEGRADED))
                         printk("continuing in degraded mode\n");
                 else {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 43f74d17bcea..501d23d3ebfd 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -71,6 +71,7 @@ int btrfs_cleanup_fs_uuids(void)
                                          dev_list);
                         if (dev->bdev) {
                                 close_bdev_excl(dev->bdev);
+                                fs_devices->open_devices--;
                         }
                         list_del(&dev->dev_list);
                         kfree(dev->name);
@@ -174,9 +175,10 @@ again:
         list_for_each(cur, head) {
                 device = list_entry(cur, struct btrfs_device, dev_list);
                 if (!device->in_fs_metadata) {
-printk("getting rid of extra dev %s\n", device->name);
-                        if (device->bdev)
+                        if (device->bdev) {
                                 close_bdev_excl(device->bdev);
+                                fs_devices->open_devices--;
+                        }
                         list_del(&device->dev_list);
                         list_del(&device->dev_alloc_list);
                         fs_devices->num_devices--;
@@ -188,6 +190,7 @@ printk("getting rid of extra dev %s\n", device->name);
         mutex_unlock(&uuid_mutex);
         return 0;
 }
+
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
         struct list_head *head = &fs_devices->devices;
@@ -199,10 +202,12 @@ int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
                 device = list_entry(cur, struct btrfs_device, dev_list);
                 if (device->bdev) {
                         close_bdev_excl(device->bdev);
+                        fs_devices->open_devices--;
                 }
                 device->bdev = NULL;
                 device->in_fs_metadata = 0;
         }
+        fs_devices->mounted = 0;
         mutex_unlock(&uuid_mutex);
         return 0;
 }
@@ -214,9 +219,19 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
         struct list_head *head = &fs_devices->devices;
         struct list_head *cur;
         struct btrfs_device *device;
-        int ret;
+        struct block_device *latest_bdev = NULL;
+        struct buffer_head *bh;
+        struct btrfs_super_block *disk_super;
+        u64 latest_devid = 0;
+        u64 latest_transid = 0;
+        u64 transid;
+        u64 devid;
+        int ret = 0;
 
         mutex_lock(&uuid_mutex);
+        if (fs_devices->mounted)
+                goto out;
+
         list_for_each(cur, head) {
                 device = list_entry(cur, struct btrfs_device, dev_list);
                 if (device->bdev)
@@ -229,21 +244,52 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 
                 if (IS_ERR(bdev)) {
                         printk("open %s failed\n", device->name);
-                        ret = PTR_ERR(bdev);
-                        goto fail;
+                        goto error;
                 }
                 set_blocksize(bdev, 4096);
-                if (device->devid == fs_devices->latest_devid)
-                        fs_devices->latest_bdev = bdev;
+
+                bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+                if (!bh)
+                        goto error_close;
+
+                disk_super = (struct btrfs_super_block *)bh->b_data;
+                if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
+                    sizeof(disk_super->magic)))
+                        goto error_brelse;
+
+                devid = le64_to_cpu(disk_super->dev_item.devid);
+                if (devid != device->devid)
+                        goto error_brelse;
+
+                transid = btrfs_super_generation(disk_super);
+                if (transid > latest_transid) {
+                        latest_devid = devid;
+                        latest_transid = transid;
+                        latest_bdev = bdev;
+                }
+
                 device->bdev = bdev;
                 device->in_fs_metadata = 0;
+                fs_devices->open_devices++;
+                continue;
 
+error_brelse:
+                brelse(bh);
+error_close:
+                close_bdev_excl(bdev);
+error:
+                continue;
         }
+        if (fs_devices->open_devices == 0) {
+                ret = -EIO;
+                goto out;
+        }
+        fs_devices->mounted = 1;
+        fs_devices->latest_bdev = latest_bdev;
+        fs_devices->latest_devid = latest_devid;
+        fs_devices->latest_trans = latest_transid;
+out:
         mutex_unlock(&uuid_mutex);
-        return 0;
-fail:
-        mutex_unlock(&uuid_mutex);
-        btrfs_close_devices(fs_devices);
         return ret;
 }
 
@@ -828,6 +874,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
         if (device->bdev) {
                 /* one close for the device struct or super_block */
                 close_bdev_excl(device->bdev);
+                root->fs_info->fs_devices->open_devices--;
         }
         if (bdev) {
                 /* one close for us */
@@ -914,6 +961,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
         list_add(&device->dev_alloc_list,
                  &root->fs_info->fs_devices->alloc_list);
         root->fs_info->fs_devices->num_devices++;
+        root->fs_info->fs_devices->open_devices++;
 out:
         btrfs_end_transaction(trans, root);
         mutex_unlock(&root->fs_info->fs_mutex);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 454fe8103329..4df6b1608f91 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -71,16 +71,16 @@ struct btrfs_fs_devices {
         /* the device with this id has the most recent coyp of the super */
         u64 latest_devid;
         u64 latest_trans;
-        u64 lowest_devid;
         u64 num_devices;
+        u64 open_devices;
         struct block_device *latest_bdev;
-        struct block_device *lowest_bdev;
         /* all of the devices in the FS */
         struct list_head devices;
 
         /* devices not currently being allocated */
         struct list_head alloc_list;
         struct list_head list;
+        int mounted;
 };
 
 struct btrfs_bio_stripe {