Re: [PATCH] cramfs: convert cramfs_blkdev_read() to use folios

[Tal Zussman <tz2294@columbia.edu>]

On 9/6/26 7:45 PM, Tal Zussman wrote:
> Read the block device pages through read_mapping_folio() and copy with
> memcpy_from_folio() instead of going through a page.
> 
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>
> ---
>  fs/cramfs/inode.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 

Following up on this - I don't see a cramfs tree, so could this go
through vfs if everything looks ok? It gets us one step closer to
removing read_mapping_page().

Thanks,
Tal

> diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
> index d4cd03f4f60d..b55eb3bd29c1 100644
> --- a/fs/cramfs/inode.c
> +++ b/fs/cramfs/inode.c
> @@ -194,7 +194,7 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
>  {
>  	struct address_space *mapping = sb->s_bdev->bd_mapping;
>  	struct file_ra_state ra = {};
> -	struct page *pages[BLKS_PER_BUF];
> +	struct folio *folios[BLKS_PER_BUF];
>  	unsigned i, blocknr, buffer;
>  	unsigned long devsize;
>  	char *data;
> @@ -227,15 +227,15 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
>  	page_cache_sync_readahead(mapping, &ra, NULL, blocknr, BLKS_PER_BUF);
>  
>  	for (i = 0; i < BLKS_PER_BUF; i++) {
> -		struct page *page = NULL;
> +		struct folio *folio = NULL;
>  
>  		if (blocknr + i < devsize) {
> -			page = read_mapping_page(mapping, blocknr + i, NULL);
> +			folio = read_mapping_folio(mapping, blocknr + i, NULL);
>  			/* synchronous error? */
> -			if (IS_ERR(page))
> -				page = NULL;
> +			if (IS_ERR(folio))
> +				folio = NULL;
>  		}
> -		pages[i] = page;
> +		folios[i] = folio;
>  	}
>  
>  	buffer = next_buffer;
> @@ -245,11 +245,14 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
>  
>  	data = read_buffers[buffer];
>  	for (i = 0; i < BLKS_PER_BUF; i++) {
> -		struct page *page = pages[i];
> +		struct folio *folio = folios[i];
>  
> -		if (page) {
> -			memcpy_from_page(data, page, 0, PAGE_SIZE);
> -			put_page(page);
> +		if (folio) {
> +			size_t offset = offset_in_folio(folio,
> +					(loff_t)(blocknr + i) << PAGE_SHIFT);
> +
> +			memcpy_from_folio(data, folio, offset, PAGE_SIZE);
> +			folio_put(folio);
>  		} else
>  			memset(data, 0, PAGE_SIZE);
>  		data += PAGE_SIZE;
> 
> ---
> base-commit: df2908090cda368b01ff43709f51890076c56157
> change-id: 20260906-cramfs-blkdev-read-folio-16fecf6908ac
> 
> Best regards,
> --  
> Tal Zussman <tz2294@columbia.edu>