[V2] target: allow changing dbroot if there are no registered devices

The target driver prevents the users from changing
the database root directory if a target module like ib_srpt has
been registered, this makes it difficult for users to
set their preferred database directory if the module
gets loaded during the system boot.

Let the users modify dbroot if there are no registered devices

v2: add a mutex to protect against possible race conditions

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
 drivers/target/target_core_configfs.c | 47 ++++++++++++++++-----------
 1 file changed, 28 insertions(+), 19 deletions(-)

On 3/28/22 5:39 AM, Maurizio Lombardi wrote:
> The target driver prevents the users from changing
> the database root directory if a target module like ib_srpt has
> been registered, this makes it difficult for users to
> set their preferred database directory if the module
> gets loaded during the system boot.
> 
> Let the users modify dbroot if there are no registered devices
> 
> v2: add a mutex to protect against possible race conditions
> 
> Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
> ---
>  drivers/target/target_core_configfs.c | 47 ++++++++++++++++-----------
>  1 file changed, 28 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
> index 023bd4516a68..fed1e7bdc013 100644
> --- a/drivers/target/target_core_configfs.c
> +++ b/drivers/target/target_core_configfs.c
> @@ -72,6 +72,9 @@ static struct config_group target_core_hbagroup;
>  static struct config_group alua_group;
>  static struct config_group alua_lu_gps_group;
>  
> +static unsigned int target_devices;
> +static DEFINE_MUTEX(target_devices_lock);
> +
>  static inline struct se_hba *
>  item_to_hba(struct config_item *item)
>  {
> @@ -105,51 +108,48 @@ static ssize_t target_core_item_dbroot_store(struct config_item *item,
>  {
>  	ssize_t read_bytes;
>  	struct file *fp;
> +	ssize_t r = -EINVAL;
>  
> -	mutex_lock(&g_tf_lock);
> -	if (!list_empty(&g_tf_list)) {
> -		mutex_unlock(&g_tf_lock);
> -		pr_err("db_root: cannot be changed: target drivers registered");
> -		return -EINVAL;
> +	mutex_lock(&target_devices_lock);
> +	if (target_devices) {
> +		pr_err("db_root: cannot be changed because it's in use\n");
> +		goto unlock;
>  	}
>  
>  	if (count > (DB_ROOT_LEN - 1)) {
> -		mutex_unlock(&g_tf_lock);
>  		pr_err("db_root: count %d exceeds DB_ROOT_LEN-1: %u\n",
>  		       (int)count, DB_ROOT_LEN - 1);
> -		return -EINVAL;
> +		goto unlock;
>  	}
>  
>  	read_bytes = snprintf(db_root_stage, DB_ROOT_LEN, "%s", page);
> -	if (!read_bytes) {
> -		mutex_unlock(&g_tf_lock);
> -		return -EINVAL;
> -	}
> +	if (!read_bytes)
> +		goto unlock;
> +
>  	if (db_root_stage[read_bytes - 1] == '\n')
>  		db_root_stage[read_bytes - 1] = '\0';
>  
>  	/* validate new db root before accepting it */
>  	fp = filp_open(db_root_stage, O_RDONLY, 0);
>  	if (IS_ERR(fp)) {
> -		mutex_unlock(&g_tf_lock);
>  		pr_err("db_root: cannot open: %s\n", db_root_stage);
> -		return -EINVAL;
> +		goto unlock;
>  	}
>  	if (!S_ISDIR(file_inode(fp)->i_mode)) {
>  		filp_close(fp, NULL);
> -		mutex_unlock(&g_tf_lock);
>  		pr_err("db_root: not a directory: %s\n", db_root_stage);
> -		return -EINVAL;
> +		goto unlock;
>  	}
>  	filp_close(fp, NULL);
>  
>  	strncpy(db_root, db_root_stage, read_bytes);
> -
> -	mutex_unlock(&g_tf_lock);
> -
>  	pr_debug("Target_Core_ConfigFS: db_root set to %s\n", db_root);
>  
> -	return read_bytes;
> +	r = read_bytes;
> +
> +unlock:
> +	mutex_unlock(&target_devices_lock);
> +	return r;
>  }
>  
>  CONFIGFS_ATTR(target_core_item_, dbroot);
> @@ -3315,6 +3315,10 @@ static struct config_group *target_core_make_subdev(
>  	 */
>  	target_stat_setup_dev_default_groups(dev);
>  
> +	mutex_lock(&target_devices_lock);
> +	target_devices++;
> +	mutex_unlock(&target_devices_lock);
> +
>  	mutex_unlock(&hba->hba_access_mutex);
>  	return &dev->dev_group;
>  
> @@ -3353,6 +3357,11 @@ static void target_core_drop_subdev(
>  	 * se_dev is released from target_core_dev_item_ops->release()
>  	 */
>  	config_item_put(item);
> +
> +	mutex_lock(&target_devices_lock);
> +	target_devices--;
> +	mutex_unlock(&target_devices_lock);
> +
>  	mutex_unlock(&hba->hba_access_mutex);
>  }
>  

Reviewed-by: Mike Christie <michael.christie@oracle.com>

Maurizio,

> The target driver prevents the users from changing the database root
> directory if a target module like ib_srpt has been registered, this
> makes it difficult for users to set their preferred database directory
> if the module gets loaded during the system boot.
>
> Let the users modify dbroot if there are no registered devices

Applied to 5.19/scsi-staging, thanks!