Re: [PATCH RFC v3 2/2] block: enable RWF_DONTCACHE for block devices

[Jan Kara <jack@suse.cz>]

On Fri 27-02-26 11:41:08, Tal Zussman wrote:
> Block device buffered reads and writes already pass through
> filemap_read() and iomap_file_buffered_write() respectively, both of
> which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
> by setting FOP_DONTCACHE in def_blk_fops.
> 
> For CONFIG_BUFFER_HEAD paths, add block_write_begin_iocb() which threads
> the kiocb through so that buffer_head-based I/O can use DONTCACHE
> behavior. The existing block_write_begin() is preserved as a wrapper
> that passes a NULL iocb.
> 
> This support is useful for databases that operate on raw block devices,
> among other userspace applications.
> 
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  block/fops.c                |  5 +++--
>  fs/buffer.c                 | 19 ++++++++++++++++---
>  include/linux/buffer_head.h |  3 +++
>  3 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index 4d32785b31d9..d8165f6ba71c 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -505,7 +505,8 @@ static int blkdev_write_begin(const struct kiocb *iocb,
>  			      unsigned len, struct folio **foliop,
>  			      void **fsdata)
>  {
> -	return block_write_begin(mapping, pos, len, foliop, blkdev_get_block);
> +	return block_write_begin_iocb(iocb, mapping, pos, len, foliop,
> +				     blkdev_get_block);
>  }
>  
>  static int blkdev_write_end(const struct kiocb *iocb,
> @@ -967,7 +968,7 @@ const struct file_operations def_blk_fops = {
>  	.splice_write	= iter_file_splice_write,
>  	.fallocate	= blkdev_fallocate,
>  	.uring_cmd	= blkdev_uring_cmd,
> -	.fop_flags	= FOP_BUFFER_RASYNC,
> +	.fop_flags	= FOP_BUFFER_RASYNC | FOP_DONTCACHE,
>  };
>  
>  static __init int blkdev_init(void)
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 838c0c571022..18f1d128bb19 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2241,14 +2241,19 @@ EXPORT_SYMBOL(block_commit_write);
>   *
>   * The filesystem needs to handle block truncation upon failure.
>   */
> -int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
> +int block_write_begin_iocb(const struct kiocb *iocb,
> +		struct address_space *mapping, loff_t pos, unsigned len,
>  		struct folio **foliop, get_block_t *get_block)
>  {
>  	pgoff_t index = pos >> PAGE_SHIFT;
> +	fgf_t fgp_flags = FGP_WRITEBEGIN;
>  	struct folio *folio;
>  	int status;
>  
> -	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
> +	if (iocb && iocb->ki_flags & IOCB_DONTCACHE)
> +		fgp_flags |= FGP_DONTCACHE;
> +
> +	folio = __filemap_get_folio(mapping, index, fgp_flags,
>  			mapping_gfp_mask(mapping));
>  	if (IS_ERR(folio))
>  		return PTR_ERR(folio);
> @@ -2263,6 +2268,13 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
>  	*foliop = folio;
>  	return status;
>  }
> +
> +int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
> +		struct folio **foliop, get_block_t *get_block)
> +{
> +	return block_write_begin_iocb(NULL, mapping, pos, len, foliop,
> +				      get_block);
> +}
>  EXPORT_SYMBOL(block_write_begin);
>  
>  int block_write_end(loff_t pos, unsigned len, unsigned copied,
> @@ -2591,7 +2603,8 @@ int cont_write_begin(const struct kiocb *iocb, struct address_space *mapping,
>  		(*bytes)++;
>  	}
>  
> -	return block_write_begin(mapping, pos, len, foliop, get_block);
> +	return block_write_begin_iocb(iocb, mapping, pos, len, foliop,
> +				     get_block);
>  }
>  EXPORT_SYMBOL(cont_write_begin);
>  
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index b16b88bfbc3e..ddf88ce290f2 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -260,6 +260,9 @@ int block_read_full_folio(struct folio *, get_block_t *);
>  bool block_is_partially_uptodate(struct folio *, size_t from, size_t count);
>  int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
>  		struct folio **foliop, get_block_t *get_block);
> +int block_write_begin_iocb(const struct kiocb *iocb,
> +		struct address_space *mapping, loff_t pos, unsigned len,
> +		struct folio **foliop, get_block_t *get_block);
>  int __block_write_begin(struct folio *folio, loff_t pos, unsigned len,
>  		get_block_t *get_block);
>  int block_write_end(loff_t pos, unsigned len, unsigned copied, struct folio *);
> 
> -- 
> 2.39.5
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR