linux-kernel - Re: [RFC PATCH 02/12] netfs: Add an iov_iter to the read subreq for the network fs/cache to use

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Date:   Wed, 21 Jul 2021 13:16:56 -0400
From:   Jeff Layton <jlayton@...hat.com>
To:     David Howells <dhowells@...hat.com>, linux-fsdevel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Mike Marshall <hubcap@...ibond.com>,
        David Wysochanski <dwysocha@...hat.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        devel@...ts.orangefs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/12] netfs: Add an iov_iter to the read subreq for
 the network fs/cache to use

On Wed, 2021-07-21 at 14:44 +0100, David Howells wrote:
> Add an iov_iter to the read subrequest and set it up to define the
> destination buffer to write into.  This will allow future patches to point
> to a bounce buffer instead for purposes of handling oversize writes,
> decryption (where we want to save the encrypted data to the cache) and
> decompression.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
> 
>  fs/afs/file.c          |    6 +-----
>  fs/netfs/read_helper.c |    5 ++++-
>  include/linux/netfs.h  |    2 ++
>  3 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/afs/file.c b/fs/afs/file.c
> index c9c21ad0e7c9..ca529f23515a 100644
> --- a/fs/afs/file.c
> +++ b/fs/afs/file.c
> @@ -319,11 +319,7 @@ static void afs_req_issue_op(struct netfs_read_subrequest *subreq)
>  	fsreq->len	= subreq->len   - subreq->transferred;
>  	fsreq->key	= subreq->rreq->netfs_priv;
>  	fsreq->vnode	= vnode;
> -	fsreq->iter	= &fsreq->def_iter;
> -
> -	iov_iter_xarray(&fsreq->def_iter, READ,
> -			&fsreq->vnode->vfs_inode.i_mapping->i_pages,
> -			fsreq->pos, fsreq->len);
> +	fsreq->iter	= &subreq->iter;
>  
>  	afs_fetch_data(fsreq->vnode, fsreq);
>  }
> diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
> index 0b6cd3b8734c..715f3e9c380d 100644
> --- a/fs/netfs/read_helper.c
> +++ b/fs/netfs/read_helper.c
> @@ -150,7 +150,7 @@ static void netfs_clear_unread(struct netfs_read_subrequest *subreq)
>  {
>  	struct iov_iter iter;
>  
> -	iov_iter_xarray(&iter, WRITE, &subreq->rreq->mapping->i_pages,
> +	iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,

What's up with the WRITE -> READ change here? Was that a preexisting
bug?

>  			subreq->start + subreq->transferred,
>  			subreq->len   - subreq->transferred);
>  	iov_iter_zero(iov_iter_count(&iter), &iter);
> @@ -745,6 +745,9 @@ netfs_rreq_prepare_read(struct netfs_read_request *rreq,
>  	if (WARN_ON(subreq->len == 0))
>  		source = NETFS_INVALID_READ;
>  
> +	iov_iter_xarray(&subreq->iter, READ, &rreq->mapping->i_pages,
> +			subreq->start, subreq->len);
> +
>  out:
>  	subreq->source = source;
>  	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index fe9887768292..5e4fafcc9480 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -17,6 +17,7 @@
>  #include <linux/workqueue.h>
>  #include <linux/fs.h>
>  #include <linux/pagemap.h>
> +#include <linux/uio.h>
>  
>  /*
>   * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
> @@ -112,6 +113,7 @@ struct netfs_cache_resources {
>  struct netfs_read_subrequest {
>  	struct netfs_read_request *rreq;	/* Supervising read request */
>  	struct list_head	rreq_link;	/* Link in rreq->subrequests */
> +	struct iov_iter		iter;		/* Iterator for this subrequest */
>  	loff_t			start;		/* Where to start the I/O */
>  	size_t			len;		/* Size of the I/O */
>  	size_t			transferred;	/* Amount of data transferred */
> 
> 

-- 
Jeff Layton <jlayton@...hat.com>