Re: [PATCH 4/4] btrfs: cleanup device states define BTRFS_DEV_STATE_CAN_DISCARD

[Nikolay Borisov <nborisov@suse.com>]

On 29.11.2017 06:45, Anand Jain wrote:
> Currently device state is being managed by each individual int
> variable such as struct btrfs_device::can_discard. Instead of that
> declare btrfs_device::dev_state BTRFS_DEV_STATE_CAN_DISCARD and use
> the bit operations.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/extent-tree.c | 3 ++-
>  fs/btrfs/volumes.c     | 6 +++---
>  fs/btrfs/volumes.h     | 2 +-
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index f81d928754e1..ee79f7cdc543 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2155,7 +2155,8 @@ int btrfs_discard_extent(struct btrfs_fs_info *fs_info, u64 bytenr,
>  
>  		for (i = 0; i < bbio->num_stripes; i++, stripe++) {
>  			u64 bytes;
> -			if (!stripe->dev->can_discard)
> +			if (!test_bit(BTRFS_DEV_STATE_CAN_DISCARD,
> +						&stripe->dev->dev_state))
>  				continue;

Given that we only check for discard support here I can't help but think
do we really need to duplicate the information. We already have struct
block_device in struct btrfs_device, why don't we query for discard
support directly the underlying device, rather than duplicating
information?

>  
>  			ret = btrfs_issue_discard(stripe->dev->bdev,
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 75839e07ce10..a9c6486f06f4 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -647,7 +647,7 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
>  
>  	q = bdev_get_queue(bdev);
>  	if (blk_queue_discard(q))
> -		device->can_discard = 1;
> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>  	if (!blk_queue_nonrot(q))
>  		fs_devices->rotating = 1;
>  
> @@ -2401,7 +2401,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>  
>  	q = bdev_get_queue(bdev);
>  	if (blk_queue_discard(q))
> -		device->can_discard = 1;
> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>  	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
>  	device->generation = trans->transid;
>  	device->io_width = fs_info->sectorsize;
> @@ -2601,7 +2601,7 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
>  
>  	q = bdev_get_queue(bdev);
>  	if (blk_queue_discard(q))
> -		device->can_discard = 1;
> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>  	mutex_lock(&fs_info->fs_devices->device_list_mutex);
>  	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
>  	device->generation = 0;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 2fbff6902c8d..85e4b2dcc071 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -50,6 +50,7 @@ struct btrfs_pending_bios {
>  #define BTRFS_DEV_STATE_WRITEABLE	(1UL << 1)
>  #define BTRFS_DEV_STATE_IN_FS_METADATA	(1UL << 2)
>  #define BTRFS_DEV_STATE_MISSING		(1UL << 3)
> +#define BTRFS_DEV_STATE_CAN_DISCARD	(1UL << 4)
>  
>  struct btrfs_device {
>  	struct list_head dev_list;
> @@ -74,7 +75,6 @@ struct btrfs_device {
>  	fmode_t mode;
>  
>  	unsigned long dev_state;
> -	int can_discard;
>  	int is_tgtdev_for_dev_replace;
>  	blk_status_t last_flush_error;
>  	int flush_bio_sent;
>