linux-kernel - Re: [PATCH v17 05/14] coda: Implement splice-read

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Date:   Mon, 13 Mar 2023 09:28:00 -0400
From:   Jan Harkes <jaharkes@...cmu.edu>
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>,
        John Hubbard <jhubbard@...dia.com>,
        linux-unionfs@...r.kernel.org
Subject: Re: [PATCH v17 05/14] coda: Implement splice-read

That actually looks better than the original code because this brings
in the experimental read intent hinting which allows userspace to
mediate access to partially cached files.

Jan


On Wed, Mar 08, 2023 at 11:53:19AM -0500, David Howells wrote:
> Implement splice-read for coda by passing the request down a layer rather
> than going through generic_file_splice_read() which is going to be changed
> to assume that ->read_folio() is present on buffered files.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Jan Harkes <jaharkes@...cmu.edu>

> cc: Jan Harkes <jaharkes@...cmu.edu>
> cc: Christoph Hellwig <hch@....de>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: John Hubbard <jhubbard@...dia.com>
> cc: David Hildenbrand <david@...hat.com>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: coda@...cmu.edu
> cc: codalist@...a.cs.cmu.edu
> cc: linux-unionfs@...r.kernel.org
> cc: linux-block@...r.kernel.org
> cc: linux-fsdevel@...r.kernel.org
> cc: linux-mm@...ck.org
> ---
> 
> Notes:
>     ver #17)
>      - Use vfs_splice_read() helper rather than open-coding checks.
> 
>  fs/coda/file.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/coda/file.c b/fs/coda/file.c
> index 3f3c81e6b1ab..12b26bd13564 100644
> --- a/fs/coda/file.c
> +++ b/fs/coda/file.c
> @@ -23,6 +23,7 @@
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
>  #include <linux/uio.h>
> +#include <linux/splice.h>
>  
>  #include <linux/coda.h>
>  #include "coda_psdev.h"
> @@ -94,6 +95,32 @@ coda_file_write_iter(struct kiocb *iocb, struct iov_iter *to)
>  	return ret;
>  }
>  
> +static ssize_t
> +coda_file_splice_read(struct file *coda_file, loff_t *ppos,
> +		      struct pipe_inode_info *pipe,
> +		      size_t len, unsigned int flags)
> +{
> +	struct inode *coda_inode = file_inode(coda_file);
> +	struct coda_file_info *cfi = coda_ftoc(coda_file);
> +	struct file *in = cfi->cfi_container;
> +	loff_t ki_pos = *ppos;
> +	ssize_t ret;
> +
> +	ret = venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
> +				  &cfi->cfi_access_intent,
> +				  len, ki_pos, CODA_ACCESS_TYPE_READ);
> +	if (ret)
> +		goto finish_read;
> +
> +	ret = vfs_splice_read(in, ppos, pipe, len, flags);
> +
> +finish_read:
> +	venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
> +			    &cfi->cfi_access_intent,
> +			    len, ki_pos, CODA_ACCESS_TYPE_READ_FINISH);
> +	return ret;
> +}
> +
>  static void
>  coda_vm_open(struct vm_area_struct *vma)
>  {
> @@ -302,5 +329,5 @@ const struct file_operations coda_file_operations = {
>  	.open		= coda_open,
>  	.release	= coda_release,
>  	.fsync		= coda_fsync,
> -	.splice_read	= generic_file_splice_read,
> +	.splice_read	= coda_file_splice_read,
>  };
> 
>