linux-ext4 - Re: [PATCH RFC v3 for-6.8/block 11/17] erofs: use bdev api

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Message-ID: <20240104120207.ig7tfc3mgckwkp2n@quack3>
Date: Thu, 4 Jan 2024 13:02:07 +0100
From: Jan Kara <jack@...e.cz>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, roger.pau@...rix.com, colyli@...e.de,
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Subject: Re: [PATCH RFC v3 for-6.8/block 11/17] erofs: use bdev api

On Thu 21-12-23 16:58:26, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> Avoid to access bd_inode directly, prepare to remove bd_inode from
> block_device.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

I'm not erofs maintainer but IMO this is quite ugly and grows erofs_buf
unnecessarily. I'd rather store 'sb' pointer in erofs_buf and then do the
right thing in erofs_bread() which is the only place that seems to care
about the erofs_is_fscache_mode() distinction... Also blkszbits is then
trivially sb->s_blocksize_bits so it would all seem much more
straightforward.

								Honza

> ---
>  fs/erofs/data.c     | 18 ++++++++++++------
>  fs/erofs/internal.h |  2 ++
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index c98aeda8abb2..bbe2fe199bf3 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -32,8 +32,8 @@ void erofs_put_metabuf(struct erofs_buf *buf)
>  void *erofs_bread(struct erofs_buf *buf, erofs_blk_t blkaddr,
>  		  enum erofs_kmap_type type)
>  {
> -	struct inode *inode = buf->inode;
> -	erofs_off_t offset = (erofs_off_t)blkaddr << inode->i_blkbits;
> +	u8 blkszbits = buf->inode ? buf->inode->i_blkbits : buf->blkszbits;
> +	erofs_off_t offset = (erofs_off_t)blkaddr << blkszbits;
>  	pgoff_t index = offset >> PAGE_SHIFT;
>  	struct page *page = buf->page;
>  	struct folio *folio;
> @@ -43,7 +43,9 @@ void *erofs_bread(struct erofs_buf *buf, erofs_blk_t blkaddr,
>  		erofs_put_metabuf(buf);
>  
>  		nofs_flag = memalloc_nofs_save();
> -		folio = read_cache_folio(inode->i_mapping, index, NULL, NULL);
> +		folio = buf->inode ?
> +			read_mapping_folio(buf->inode->i_mapping, index, NULL) :
> +			bdev_read_folio(buf->bdev, offset);
>  		memalloc_nofs_restore(nofs_flag);
>  		if (IS_ERR(folio))
>  			return folio;
> @@ -67,10 +69,14 @@ void *erofs_bread(struct erofs_buf *buf, erofs_blk_t blkaddr,
>  
>  void erofs_init_metabuf(struct erofs_buf *buf, struct super_block *sb)
>  {
> -	if (erofs_is_fscache_mode(sb))
> +	if (erofs_is_fscache_mode(sb)) {
>  		buf->inode = EROFS_SB(sb)->s_fscache->inode;
> -	else
> -		buf->inode = sb->s_bdev->bd_inode;
> +		buf->bdev = NULL;
> +	} else {
> +		buf->inode = NULL;
> +		buf->bdev = sb->s_bdev;
> +		buf->blkszbits = EROFS_SB(sb)->blkszbits;
> +	}
>  }
>  
>  void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index b0409badb017..c9206351b485 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -224,8 +224,10 @@ enum erofs_kmap_type {
>  
>  struct erofs_buf {
>  	struct inode *inode;
> +	struct block_device *bdev;
>  	struct page *page;
>  	void *base;
> +	u8 blkszbits;
>  	enum erofs_kmap_type kmap_type;
>  };
>  #define __EROFS_BUF_INITIALIZER	((struct erofs_buf){ .page = NULL })
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR