Re: [PATCH 1/2] iomap: support tail packing inline read

[Christoph Hellwig]

On Sat, Jul 17, 2021 at 09:38:18PM +0800, Gao Xiang wrote:
> >From 62f367245492e389711bcebbf7da5adae586299f Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@xxxxxx>
> Date: Fri, 16 Jul 2021 10:52:48 +0200
> Subject: [PATCH] iomap: support tail packing inline read

I'd still credit this to you as you did all the hard work.

> +	/* inline source data must be inside a single page */
> +	BUG_ON(iomap->length > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	/* handle tail-packing blocks cross the current page into the next */
> +	if (size > PAGE_SIZE - poff)
> +		size = PAGE_SIZE - poff;

This should probably use min or min_t.

>  
>  	addr = kmap_atomic(page);
> -	memcpy(addr, iomap->inline_data, size);
> -	memset(addr + size, 0, PAGE_SIZE - size);
> +	memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
> +	memset(addr + poff + size, 0, PAGE_SIZE - poff - size);
>  	kunmap_atomic(addr);
> -	SetPageUptodate(page);
> +	flush_dcache_page(page);

The flush_dcache_page addition should be a separate patch.

>  
>  	if (dio->flags & IOMAP_DIO_WRITE) {
>  		loff_t size = inode->i_size;
> @@ -394,7 +395,8 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
>  			mark_inode_dirty(inode);
>  		}
>  	} else {
> -		copied = copy_to_iter(iomap->inline_data + pos, length, iter);
> +		copied = copy_to_iter(iomap->inline_data + pos - iomap->offset,
> +				length, iter);

We also need to take the offset into account for the write side.
I guess it would be nice to have a local variable for the inline
address to not duplicate that calculation multiple times.