linux-ext4 - [PATCH v22 08/31] splice: Make splice from a DAX file use copy_splice

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Date:   Mon, 22 May 2023 14:49:55 +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>, Theodore Ts'o <tytso@....edu>,
        Gao Xiang <hsiangkao@...ux.alibaba.com>,
        linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: [PATCH v22 08/31] splice: Make splice from a DAX file use copy_splice_read()

Make a read splice from a DAX file go directly to copy_splice_read() to do
the reading as filemap_splice_read() is unlikely to find any pagecache to
splice.

I think this affects only erofs, Ext2, Ext4, fuse and XFS.

Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Christian Brauner <brauner@...nel.org>
Reviewed-by: Theodore Ts'o <tytso@....edu>
Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
cc: Al Viro <viro@...iv.linux.org.uk>
cc: Jens Axboe <axboe@...nel.dk>
cc: linux-erofs@...ts.ozlabs.org
cc: linux-ext4@...r.kernel.org
cc: linux-xfs@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
cc: linux-block@...r.kernel.org
cc: linux-mm@...ck.org
---

Notes:
    ver #21)
     - Don't need #ifdef CONFIG_FS_DAX as IS_DAX() is false if !CONFIG_FS_DAX.
     - Needs to be in vfs_splice_read(), not generic_file_splice_read().

 fs/splice.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 76126b1aafcb..8268248df3a9 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -908,10 +908,10 @@ long vfs_splice_read(struct file *in, loff_t *ppos,
 	if (unlikely(!in->f_op->splice_read))
 		return warn_unsupported(in, "read");
 	/*
-	 * O_DIRECT doesn't deal with the pagecache, so we allocate a buffer,
-	 * copy into it and splice that into the pipe.
+	 * O_DIRECT and DAX don't deal with the pagecache, so we allocate a
+	 * buffer, copy into it and splice that into the pipe.
 	 */
-	if ((in->f_flags & O_DIRECT))
+	if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host))
 		return copy_splice_read(in, ppos, pipe, len, flags);
 	return in->f_op->splice_read(in, ppos, pipe, len, flags);
 }