linux-kernel - Re: [PATCH v9 01/10] iomap: stash iomap read ctx in the private field of iomap

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Message-ID: <f3938037-1292-470d-aace-e5c620428a1d@linux.alibaba.com>
Date: Tue, 18 Nov 2025 01:08:56 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: brauner@...nel.org, djwong@...nel.org
Cc: linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, Chao Yu <chao@...nel.org>,
 Amir Goldstein <amir73il@...il.com>, Joanne Koong <joannelkoong@...il.com>,
 Hongbo Li <lihongbo22@...wei.com>
Subject: Re: [PATCH v9 01/10] iomap: stash iomap read ctx in the private field
 of iomap_iter

Hi Darrick, Christian,

On 2025/11/17 21:25, Hongbo Li wrote:
> It's useful to get filesystem-specific information using the
> existing private field in the @iomap_iter passed to iomap_{begin,end}
> for advanced usage for iomap buffered reads, which is much like the
> current iomap DIO.
> 
> For example, EROFS needs it to:
> 
>   - implement an efficient page cache sharing feature, since iomap
>     needs to apply to anon inode page cache but we'd like to get the
>     backing inode/fs instead, so filesystem-specific private data is
>     needed to keep such information;
> 
>   - pass in both struct page * and void * for inline data to avoid
>     kmap_to_page() usage (which is bogus).
> 
> Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22@...wei.com>

Could you help review this iomap change, since erofs uses iomap
and erofs page cache sharing needs this change, as I told
Joanne months ago.

Even without the page cache sharing feature, introducing
iomap_iter_ctx for .iomap_{begin,end}, like the current DIO
does, is still useful for erofs, as patch 2 mentioned.

Thanks,
Gao XIang