btrfs: add a btrfs_get_dev_args_from_path helperNotice: this object is not reachable from any branch.

We are going to want to populate our device lookup args outside of any
locks and then do the actual device lookup later, so add a helper to do
this work and make btrfs_find_device_by_devspec() use this helper for
now.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Notice: this object is not reachable from any branch.

2 files changed, 68 insertions, 32 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 40803d8a742f4..4a2322b9d35b4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2330,45 +2330,81 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
 	btrfs_free_device(tgtdev);
 }
 
-static struct btrfs_device *btrfs_find_device_by_path(
-		struct btrfs_fs_info *fs_info, const char *device_path)
+/**
+ * Populate args from device at path
+ *
+ * @fs_info:	the filesystem
+ * @args:	the args to populate
+ * @path:	the path to the device
+ *
+ * This will read the super block of the device at @path and populate @args with
+ * the devid, fsid, and uuid.  This is meant to be used for ioctls that need to
+ * lookup a device to operate on, but need to do it before we take any locks.
+ * This properly handles the special case of "missing" that a user may pass in,
+ * and does some basic sanity checks.  The caller must make sure that @path is
+ * properly NUL terminated before calling in, and must call
+ * btrfs_put_dev_args_from_path() in order to free up the temporary fsid and
+ * uuid buffers.
+ *
+ * Return: 0 for success, -errno for failure
+ */
+int btrfs_get_dev_args_from_path(struct btrfs_fs_info *fs_info,
+				 struct btrfs_dev_lookup_args *args,
+				 const char *path)
 {
-	BTRFS_DEV_LOOKUP_ARGS(args);
-	int ret = 0;
 	struct btrfs_super_block *disk_super;
 	struct block_device *bdev;
-	struct btrfs_device *device;
+	int ret;
 
-	ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
-				    fs_info->bdev_holder, 0, &bdev, &disk_super);
-	if (ret)
-		return ERR_PTR(ret);
+	if (!path || !path[0])
+		return -EINVAL;
+	if (!strcmp(path, "missing")) {
+		args->missing = true;
+		return 0;
+	}
+
+	args->uuid = kzalloc(BTRFS_UUID_SIZE, GFP_KERNEL);
+	args->fsid = kzalloc(BTRFS_FSID_SIZE, GFP_KERNEL);
+	if (!args->uuid || !args->fsid) {
+		btrfs_put_dev_args_from_path(args);
+		return -ENOMEM;
+	}
 
-	args.devid = btrfs_stack_device_id(&disk_super->dev_item);
-	args.uuid = disk_super->dev_item.uuid;
+	ret = btrfs_get_bdev_and_sb(path, FMODE_READ, fs_info->bdev_holder, 0,
+				    &bdev, &disk_super);
+	if (ret)
+		return ret;
+	args->devid = btrfs_stack_device_id(&disk_super->dev_item);
+	memcpy(args->uuid, disk_super->dev_item.uuid, BTRFS_UUID_SIZE);
 	if (btrfs_fs_incompat(fs_info, METADATA_UUID))
-		args.fsid = disk_super->metadata_uuid;
+		memcpy(args->fsid, disk_super->metadata_uuid, BTRFS_FSID_SIZE);
 	else
-		args.fsid = disk_super->fsid;
-
-	device = btrfs_find_device(fs_info->fs_devices, &args);
-
+		memcpy(args->fsid, disk_super->fsid, BTRFS_FSID_SIZE);
 	btrfs_release_disk_super(disk_super);
-	if (!device)
-		device = ERR_PTR(-ENOENT);
 	blkdev_put(bdev, FMODE_READ);
-	return device;
+	return 0;
 }
 
 /*
- * Lookup a device given by device id, or the path if the id is 0.
+ * Only use this jointly with btrfs_get_dev_args_from_path() because we will
+ * allocate our ->uuid and ->fsid pointers, everybody else uses local variables
+ * that don't need to be freed.
  */
+void btrfs_put_dev_args_from_path(struct btrfs_dev_lookup_args *args)
+{
+	kfree(args->uuid);
+	kfree(args->fsid);
+	args->uuid = NULL;
+	args->fsid = NULL;
+}
+
 struct btrfs_device *btrfs_find_device_by_devspec(
 		struct btrfs_fs_info *fs_info, u64 devid,
 		const char *device_path)
 {
 	BTRFS_DEV_LOOKUP_ARGS(args);
 	struct btrfs_device *device;
+	int ret;
 
 	if (devid) {
 		args.devid = devid;
@@ -2378,18 +2414,14 @@ struct btrfs_device *btrfs_find_device_by_devspec(
 		return device;
 	}
 
-	if (!device_path || !device_path[0])
-		return ERR_PTR(-EINVAL);
-
-	if (strcmp(device_path, "missing") == 0) {
-		args.missing = true;
-		device = btrfs_find_device(fs_info->fs_devices, &args);
-		if (!device)
-			return ERR_PTR(-ENOENT);
-		return device;
-	}
-
-	return btrfs_find_device_by_path(fs_info, device_path);
+	ret = btrfs_get_dev_args_from_path(fs_info, &args, device_path);
+	if (ret)
+		return ERR_PTR(ret);
+	device = btrfs_find_device(fs_info->fs_devices, &args);
+	btrfs_put_dev_args_from_path(&args);
+	if (!device)
+		return ERR_PTR(-ENOENT);
+	return device;
 }
 
 /*
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index bdcf7641e0bb7..acf7c1307e147 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -520,9 +520,13 @@ void btrfs_assign_next_active_device(struct btrfs_device *device,
 struct btrfs_device *btrfs_find_device_by_devspec(struct btrfs_fs_info *fs_info,
 						  u64 devid,
 						  const char *devpath);
+int btrfs_get_dev_args_from_path(struct btrfs_fs_info *fs_info,
+				 struct btrfs_dev_lookup_args *args,
+				 const char *path);
 struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
 					const u64 *devid,
 					const u8 *uuid);
+void btrfs_put_dev_args_from_path(struct btrfs_dev_lookup_args *args);
 void btrfs_free_device(struct btrfs_device *device);
 int btrfs_rm_device(struct btrfs_fs_info *fs_info,
 		    const char *device_path, u64 devid,