linux-kernel - [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof where appropriate

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Message-Id: <20230519074047.1739879-4-dhowells@redhat.com>
Date:   Fri, 19 May 2023 08:40:18 +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>
Subject: [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof where appropriate

Make direct_read_splice() limit the read to the end of the file for regular
files and block devices, thereby reducing the amount of allocation it will
do in such a case.

This means that the blockdev code doesn't require any special handling as
filemap_read_splice() also limits to i_size.

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: linux-block@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
cc: linux-mm@...ck.org
---
 fs/splice.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/splice.c b/fs/splice.c
index 4db3eee49423..89c8516554d1 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -315,6 +315,19 @@ ssize_t direct_splice_read(struct file *in, loff_t *ppos,
 	size_t used, npages, chunk, remain, keep = 0;
 	int i;
 
+	if (!len)
+		return 0;
+
+	if (S_ISREG(file_inode(in)->i_mode) ||
+	    S_ISBLK(file_inode(in)->i_mode)) {
+		loff_t i_size = i_size_read(in->f_mapping->host);
+
+		if (*ppos >= i_size)
+			return 0;
+		if (len > i_size - *ppos)
+			len = i_size - *ppos;
+	}
+
 	/* Work out how much data we can actually add into the pipe */
 	used = pipe_occupancy(pipe->head, pipe->tail);
 	npages = max_t(ssize_t, pipe->max_usage - used, 0);