Re: [PATCH v2 1/3] btrfs: introduce BTRFS_EXCLOP_BALANCE_PAUSED exclusive state

[Josef Bacik <josef@toxicpanda.com>]

On Mon, Nov 08, 2021 at 04:28:18PM +0200, Nikolay Borisov wrote:
> Current set of exclusive operation states is not sufficient to handle all
> practical use cases. In particular there is a need to be able to add a
> device to a filesystem that have paused balance. Currently there is no
> way to distinguish between a running and a paused balance. Fix this by
> introducing BTRFS_EXCLOP_BALANCE_PAUSED which is going to be set in 2
> occasions:
> 
> 1. When a filesystem is mounted with skip_balance and there is an
>    unfinished balance it will now be into BALANCE_PAUSED instead of
>    simply BALANCE state.
> 
> 2. When a running balance is paused.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/ctree.h   |  3 +++
>  fs/btrfs/ioctl.c   | 13 +++++++++++++
>  fs/btrfs/volumes.c | 11 +++++++++--
>  3 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 7553e9dc5f93..8376271bfed1 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -613,6 +613,7 @@ enum {
>   */
>  enum btrfs_exclusive_operation {
>  	BTRFS_EXCLOP_NONE,
> +	BTRFS_EXCLOP_BALANCE_PAUSED,
>  	BTRFS_EXCLOP_BALANCE,
>  	BTRFS_EXCLOP_DEV_ADD,
>  	BTRFS_EXCLOP_DEV_REMOVE,
> @@ -3305,6 +3306,8 @@ bool btrfs_exclop_start_try_lock(struct btrfs_fs_info *fs_info,
>  				 enum btrfs_exclusive_operation type);
>  void btrfs_exclop_start_unlock(struct btrfs_fs_info *fs_info);
>  void btrfs_exclop_finish(struct btrfs_fs_info *fs_info);
> +void btrfs_exclop_pause_balance(struct btrfs_fs_info *fs_info);
> +
>  
>  /* file.c */
>  int __init btrfs_auto_defrag_init(void);
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 92424a22d8d6..f4c05a9aab84 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -414,6 +414,15 @@ void btrfs_exclop_finish(struct btrfs_fs_info *fs_info)
>  	sysfs_notify(&fs_info->fs_devices->fsid_kobj, NULL, "exclusive_operation");
>  }
>  
> +void btrfs_exclop_pause_balance(struct btrfs_fs_info *fs_info)
> +{
> +	spin_lock(&fs_info->super_lock);
> +	ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE ||
> +	       fs_info->exclusive_operation == BTRFS_EXCLOP_DEV_ADD);
> +	fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE_PAUSED;
> +	spin_unlock(&fs_info->super_lock);
> +}
> +
>  static int btrfs_ioctl_getversion(struct file *file, int __user *arg)
>  {
>  	struct inode *inode = file_inode(file);
> @@ -4020,6 +4029,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
>  			if (fs_info->balance_ctl &&
>  			    !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
>  				/* this is (3) */
> +				spin_lock(&fs_info->super_lock);
> +				ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED);
> +				fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE;
> +				spin_unlock(&fs_info->super_lock);
>  				need_unlock = false;
>  				goto locked;
>  			}
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index cc80f2a97a0b..e87f9ac440c2 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4355,8 +4355,10 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
>  	ret = __btrfs_balance(fs_info);
>  
>  	mutex_lock(&fs_info->balance_mutex);
> -	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req))
> +	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) {
>  		btrfs_info(fs_info, "balance: paused");
> +		btrfs_exclop_pause_balance(fs_info);
> +	}
>  	/*
>  	 * Balance can be canceled by:
>  	 *
> @@ -4406,6 +4408,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
>  static int balance_kthread(void *data)
>  {
>  	struct btrfs_fs_info *fs_info = data;
> +	bool paused = false;

Unused variable.  Thanks,

Josef