linux-kernel - [PATCH v20 24/32] splice: Do splice read from a file without using ITER

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Message-Id: <20230519074047.1739879-25-dhowells@redhat.com>
Date:   Fri, 19 May 2023 08:40:39 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        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>,
        Steve French <smfrench@...il.com>,
        John Hubbard <jhubbard@...dia.com>, linux-cifs@...r.kernel.org
Subject: [PATCH v20 24/32] splice: Do splice read from a file without using ITER_PIPE

Make generic_file_splice_read() use filemap_splice_read() and
direct_splice_read() rather than using an ITER_PIPE and call_read_iter().

With this, ITER_PIPE is no longer used.

Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: 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: David Hildenbrand <david@...hat.com>
cc: John Hubbard <jhubbard@...dia.com>
cc: linux-mm@...ck.org
cc: linux-block@...r.kernel.org
cc: linux-cifs@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
---

Notes:
    ver #20)
     - Use s_maxbytes from the backing store (in->f_mapping), not the front
       inode (especially for a blockdev).
    
    ver #18)
     - Split out the change to cifs to make it use generic_file_splice_read().
     - Split out the unexport of filemap_splice_read() (still needed by cifs).

 fs/splice.c | 31 +++++++------------------------
 1 file changed, 7 insertions(+), 24 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 7b818b5b18d4..56d9802729d0 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -417,34 +417,17 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 				 struct pipe_inode_info *pipe, size_t len,
 				 unsigned int flags)
 {
-	struct iov_iter to;
-	struct kiocb kiocb;
-	int ret;
-
+	if (unlikely(*ppos >= in->f_mapping->host->i_sb->s_maxbytes))
+		return 0;
+	if (unlikely(!len))
+		return 0;
 #ifdef CONFIG_FS_DAX
 	if (IS_DAX(in->f_mapping->host))
 		return direct_splice_read(in, ppos, pipe, len, flags);
 #endif
-
-	iov_iter_pipe(&to, ITER_DEST, pipe, len);
-	init_sync_kiocb(&kiocb, in);
-	kiocb.ki_pos = *ppos;
-	ret = call_read_iter(in, &kiocb, &to);
-	if (ret > 0) {
-		*ppos = kiocb.ki_pos;
-		file_accessed(in);
-	} else if (ret < 0) {
-		/* free what was emitted */
-		pipe_discard_from(pipe, to.start_head);
-		/*
-		 * callers of ->splice_read() expect -EAGAIN on
-		 * "can't put anything in there", rather than -EFAULT.
-		 */
-		if (ret == -EFAULT)
-			ret = -EAGAIN;
-	}
-
-	return ret;
+	if ((in->f_flags & O_DIRECT))
+		return direct_splice_read(in, ppos, pipe, len, flags);
+	return filemap_splice_read(in, ppos, pipe, len, flags);
 }
 EXPORT_SYMBOL(generic_file_splice_read);