linux-kernel - Re: [PATCH v21 03/30] splice: Rename direct_splice_read() to copy_splice

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Date:   Mon, 22 May 2023 14:53:31 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>,
        Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org
Subject: Re: [PATCH v21 03/30] splice: Rename direct_splice_read() to
 copy_splice_read()

On Mon, May 22, 2023 at 08:55:14AM +0100, David Howells wrote:
> > For the future it'd be nice if exported functions would always get
> > proper kernel doc,
> 
> Something like the attached?
> 
> David
> ---
> commit 0362042ba0751fc5457b0548fb9006f9d7dfbeca
> Author: David Howells <dhowells@...hat.com>
> Date:   Mon May 22 08:34:24 2023 +0100
> 
>     splice: kdoc for filemap_splice_read() and copy_splice_read()
>     
>     Provide kerneldoc comments for filemap_splice_read() and
>     copy_splice_read().
>     
>     Signed-off-by: David Howells <dhowells@...hat.com>
>     cc: Christian Brauner <brauner@...nel.org>
>     cc: Christoph Hellwig <hch@....de>
>     cc: Jens Axboe <axboe@...nel.dk>
>     cc: Steve French <smfrench@...il.com>
>     cc: Al Viro <viro@...iv.linux.org.uk>
>     cc: linux-mm@...ck.org
>     cc: linux-block@...r.kernel.org
>     cc: linux-cifs@...r.kernel.org
>     cc: linux-fsdevel@...r.kernel.org
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 9be4cb3b9879..5292a8fa929d 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -299,8 +299,25 @@ void splice_shrink_spd(struct splice_pipe_desc *spd)
>  	kfree(spd->partial);
>  }
>  
> -/*
> - * Copy data from a file into pages and then splice those into the output pipe.
> +/**
> + * copy_splice_read -  Copy data from a file and splice the copy into a pipe
> + * @in: The file to read from
> + * @ppos: Pointer to the file position to read from
> + * @pipe: The pipe to splice into
> + * @len: The amount to splice
> + * @flags: The SPLICE_F_* flags
> + *
> + * This function allocates a bunch of pages sufficient to hold the requested
> + * amount of data (but limited by the remaining pipe capacity), passes it to
> + * the file's ->read_iter() to read into and then splices the used pages into
> + * the pipe.
> + *
> + * On success, the number of bytes read will be returned and *@...s will be
> + * updated if appropriate; 0 will be returned if there is no more data to be
> + * read; -EAGAIN will be returned if the pipe had no space, and some other
> + * negative error code will be returned on error.  A short read may occur if
> + * the pipe has insufficient space, we reach the end of the data or we hit a
> + * hole.
>   */

I think kdoc expects:

* Return: On success, the number of bytes read will be returned and *@...s will be
* updated if appropriate; 0 will be returned if there is no more data to be
* read; -EAGAIN will be returned if the pipe had no space, and some other
* negative error code will be returned on error.  A short read may occur if
* the pipe has insufficient space, we reach the end of the data or we hit a
* hole.

and similar for filemap_splice_read() other than that this looks good!

>  ssize_t copy_splice_read(struct file *in, loff_t *ppos,
>  			 struct pipe_inode_info *pipe,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 603b562d69b1..1f235a6430fd 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2871,9 +2871,24 @@ size_t splice_folio_into_pipe(struct pipe_inode_info *pipe,
>  	return spliced;
>  }
>  
> -/*
> - * Splice folios from the pagecache of a buffered (ie. non-O_DIRECT) file into
> - * a pipe.
> +/**
> + * filemap_splice_read -  Splice data from a file's pagecache into a pipe
> + * @in: The file to read from
> + * @ppos: Pointer to the file position to read from
> + * @pipe: The pipe to splice into
> + * @len: The amount to splice
> + * @flags: The SPLICE_F_* flags
> + *
> + * This function gets folios from a file's pagecache and splices them into the
> + * pipe.  Readahead will be called as necessary to fill more folios.  This may
> + * be used for blockdevs also.
> + *
> + * On success, the number of bytes read will be returned and *@...s will be
> + * updated if appropriate; 0 will be returned if there is no more data to be
> + * read; -EAGAIN will be returned if the pipe had no space, and some other
> + * negative error code will be returned on error.  A short read may occur if
> + * the pipe has insufficient space, we reach the end of the data or we hit a
> + * hole.
>   */
>  ssize_t filemap_splice_read(struct file *in, loff_t *ppos,
>  			    struct pipe_inode_info *pipe,
>