Re: [PATCH 11/13] btrfs: open code set_io_stripe for RAID56

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 13.12.23 09:58, Christoph Hellwig wrote:
> 
> I think raid stripe tree handling also really should move out of
> set_io_stripe.  Below is the latest I have, although it probably won't
> apply to your tree:

I've decided to add that one afterwards giving the attribution to you.
There are some other patches in your tree as well, which I want to have 
a look at too.

> ---
>  From ac208da48d7f9d11eef8a01ac0c6fbf9681665b5 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Thu, 22 Jun 2023 05:53:13 +0200
> Subject: btrfs: move raid-stripe-tree handling out of set_io_stripe
> 
> set_io_stripe gets a little too complicated with the raid-stripe-tree
> handling.  Move it out into the only callers that actually needs it.
> 
> The only reads with more than a single stripe is the parity raid recovery
> case thast will need very special handling anyway once implemented.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/btrfs/volumes.c | 61 ++++++++++++++++++++--------------------------
>   1 file changed, 27 insertions(+), 34 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 30ee5d1670d034..e32eefa242b0a4 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6233,22 +6233,12 @@ static u64 btrfs_max_io_len(struct map_lookup *map, enum btrfs_map_op op,
>   	return U64_MAX;
>   }
>   
> -static int set_io_stripe(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> -		      u64 logical, u64 *length, struct btrfs_io_stripe *dst,
> -		      struct map_lookup *map, u32 stripe_index,
> -		      u64 stripe_offset, u64 stripe_nr)
> +static void set_io_stripe(struct btrfs_io_stripe *dst, const struct map_lookup *map,
> +			  u32 stripe_index, u64 stripe_offset, u32 stripe_nr)
>   {
>   	dst->dev = map->stripes[stripe_index].dev;
> -
> -	if (op == BTRFS_MAP_READ &&
> -	    btrfs_use_raid_stripe_tree(fs_info, map->type))
> -		return btrfs_get_raid_extent_offset(fs_info, logical, length,
> -						    map->type, stripe_index,
> -						    dst);
> -
>   	dst->physical = map->stripes[stripe_index].physical +
>   			stripe_offset + ((u64)stripe_nr << BTRFS_STRIPE_LEN_SHIFT);
> -	return 0;
>   }
>   
>   int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
> @@ -6423,15 +6413,24 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
>   	 * physical block information on the stack instead of allocating an
>   	 * I/O context structure.
>   	 */
> -	if (smap && num_alloc_stripes == 1 &&
> -	    !(btrfs_use_raid_stripe_tree(fs_info, map->type) &&
> -	      op != BTRFS_MAP_READ) &&
> -	    !((map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) && mirror_num > 1)) {
> -		ret = set_io_stripe(fs_info, op, logical, length, smap, map,
> -				    stripe_index, stripe_offset, stripe_nr);
> -		*mirror_num_ret = mirror_num;
> -		*bioc_ret = NULL;
> -		goto out;
> +	if (smap && num_alloc_stripes == 1) {
> +		if (op == BTRFS_MAP_READ &&
> +		    btrfs_use_raid_stripe_tree(fs_info, map->type)) {
> +			ret = btrfs_get_raid_extent_offset(fs_info, logical,
> +							   length, map->type,
> +							   stripe_index, smap);
> +			*mirror_num_ret = mirror_num;
> +			*bioc_ret = NULL;
> +			goto out;
> +		} else if (!(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) ||
> +			   mirror_num == 0) {
> +			set_io_stripe(smap, map, stripe_index, stripe_offset,
> +				      stripe_nr);
> +			*mirror_num_ret = mirror_num;
> +			*bioc_ret = NULL;
> +			ret = 0;
> +			goto out;
> +		}
>   	}
>   
>   	bioc = alloc_btrfs_io_context(fs_info, logical, num_alloc_stripes);
> @@ -6448,6 +6447,8 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
>   	 *
>   	 * It's still mostly the same as other profiles, just with extra rotation.
>   	 */
> +	ASSERT(op != BTRFS_MAP_READ ||
> +	       btrfs_use_raid_stripe_tree(fs_info, map->type));
>   	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
>   	    (op != BTRFS_MAP_READ || mirror_num > 1)) {
>   		/*
> @@ -6461,29 +6462,21 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
>   		bioc->full_stripe_logical = em->start +
>   			((stripe_nr * data_stripes) << BTRFS_STRIPE_LEN_SHIFT);
>   		for (i = 0; i < num_stripes; i++)
> -			ret = set_io_stripe(fs_info, op, logical, length,
> -					    &bioc->stripes[i], map,
> -					    (i + stripe_nr) % num_stripes,
> -					    stripe_offset, stripe_nr);
> +			set_io_stripe(&bioc->stripes[i], map,
> +				      (i + stripe_nr) % num_stripes,
> +				      stripe_offset, stripe_nr);
>   	} else {
>   		/*
>   		 * For all other non-RAID56 profiles, just copy the target
>   		 * stripe into the bioc.
>   		 */
>   		for (i = 0; i < num_stripes; i++) {
> -			ret = set_io_stripe(fs_info, op, logical, length,
> -					    &bioc->stripes[i], map, stripe_index,
> -					    stripe_offset, stripe_nr);
> +			set_io_stripe(&bioc->stripes[i], map, stripe_index,
> +				      stripe_offset, stripe_nr);
>   			stripe_index++;
>   		}
>   	}
>   
> -	if (ret) {
> -		*bioc_ret = NULL;
> -		btrfs_put_bioc(bioc);
> -		goto out;
> -	}
> -
>   	if (op != BTRFS_MAP_READ)
>   		max_errors = btrfs_chunk_max_errors(map);
>