linux-kernel - Re: [PATCH v22 25/31] zonefs: Provide a splice-read wrapper

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Message-ID: <12153db1-20af-040b-ded0-31286b5bafca@kernel.org>
Date:   Tue, 23 May 2023 11:48:17 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     David Howells <dhowells@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
Cc:     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>,
        Christian Brauner <brauner@...nel.org>,
        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>,
        "Darrick J . Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v22 25/31] zonefs: Provide a splice-read wrapper

On 5/22/23 22:50, David Howells wrote:
> Provide a splice_read wrapper for zonefs.  This does some checks before
> proceeding and locks the inode across the call to filemap_splice_read() and
> a size check in case of truncation.  Splicing from direct I/O is handled by
> the caller.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Christoph Hellwig <hch@....de>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Darrick J. Wong <djwong@...nel.org>
> cc: linux-xfs@...r.kernel.org
> cc: linux-fsdevel@...r.kernel.org
> cc: linux-block@...r.kernel.org
> cc: linux-mm@...ck.org

One comment below but otherwise looks OK.

Acked-by: Damien Le Moal <dlemoal@...nel.org>

> ---
>  fs/zonefs/file.c | 40 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/zonefs/file.c b/fs/zonefs/file.c
> index 132f01d3461f..65d4c4fe6364 100644
> --- a/fs/zonefs/file.c
> +++ b/fs/zonefs/file.c
> @@ -752,6 +752,44 @@ static ssize_t zonefs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	return ret;
>  }
>  
> +static ssize_t zonefs_file_splice_read(struct file *in, loff_t *ppos,
> +				       struct pipe_inode_info *pipe,
> +				       size_t len, unsigned int flags)
> +{
> +	struct inode *inode = file_inode(in);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	struct zonefs_zone *z = zonefs_inode_zone(inode);
> +	loff_t isize;
> +	ssize_t ret = 0;
> +
> +	/* Offline zones cannot be read */
> +	if (unlikely(IS_IMMUTABLE(inode) && !(inode->i_mode & 0777)))
> +		return -EPERM;
> +
> +	if (*ppos >= z->z_capacity)
> +		return 0;
> +
> +	inode_lock_shared(inode);
> +
> +	/* Limit read operations to written data */
> +	mutex_lock(&zi->i_truncate_mutex);
> +	isize = i_size_read(inode);
> +	if (*ppos >= isize)
> +		len = 0;
> +	else
> +		len = min_t(loff_t, len, isize - *ppos);
> +	mutex_unlock(&zi->i_truncate_mutex);
> +
> +	if (len > 0) {
> +		ret = filemap_splice_read(in, ppos, pipe, len, flags);
> +		if (ret == -EIO)

Is -EIO the only error that filemap_splice_read() may return ? There are other
IO error codes that we could get from the block layer, e.g. -ETIMEDOUT etc. So
"if (ret < 0)" may be better here ?

> +			zonefs_io_error(inode, false);
> +	}
> +
> +	inode_unlock_shared(inode);
> +	return ret;
> +}
> +
>  /*
>   * Write open accounting is done only for sequential files.
>   */
> @@ -896,7 +934,7 @@ const struct file_operations zonefs_file_operations = {
>  	.llseek		= zonefs_file_llseek,
>  	.read_iter	= zonefs_file_read_iter,
>  	.write_iter	= zonefs_file_write_iter,
> -	.splice_read	= generic_file_splice_read,
> +	.splice_read	= zonefs_file_splice_read,
>  	.splice_write	= iter_file_splice_write,
>  	.iopoll		= iocb_bio_iopoll,
>  };
> 

-- 
Damien Le Moal
Western Digital Research