linux-kernel - [RFC PATCH 36/37] clean up copy_mc_pipe_to

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Date:   Sun,  6 Jun 2021 19:10:50 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Sterba <dsterba@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Anton Altaparmakov <anton@...era.com>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC PATCH 36/37] clean up copy_mc_pipe_to_iter()

... and we don't need kmap_atomic() there - kmap_local_page() is fine.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 33 +++++++++------------------------
 1 file changed, 9 insertions(+), 24 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 7471fb181643..0ee359b62afc 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -653,19 +653,6 @@ static int copyout_mc(void __user *to, const void *from, size_t n)
 	return n;
 }
 
-static unsigned long copy_mc_to_page(struct page *page, size_t offset,
-		const char *from, size_t len)
-{
-	unsigned long ret;
-	char *to;
-
-	to = kmap_atomic(page);
-	ret = copy_mc_to_kernel(to + offset, from, len);
-	kunmap_atomic(to);
-
-	return ret;
-}
-
 static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
 				struct iov_iter *i)
 {
@@ -677,25 +664,23 @@ static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
 	if (!sanity(i))
 		return 0;
 
-	bytes = n = push_pipe(i, bytes, &i_head, &off);
-	if (unlikely(!n))
-		return 0;
-	do {
+	n = push_pipe(i, bytes, &i_head, &off);
+	while (n) {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
+		char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
 		unsigned long rem;
-
-		rem = copy_mc_to_page(pipe->bufs[i_head & p_mask].page,
-					    off, addr, chunk);
+		rem = copy_mc_to_kernel(p + off, addr + xfer, chunk);
+		chunk -= rem;
+		kunmap_local(p);
 		i->head = i_head;
-		i->iov_offset = off + chunk - rem;
-		xfer += chunk - rem;
+		i->iov_offset = off + chunk;
+		xfer += chunk;
 		if (rem)
 			break;
 		n -= chunk;
-		addr += chunk;
 		off = 0;
 		i_head++;
-	} while (n);
+	}
 	i->count -= xfer;
 	return xfer;
 }
-- 
2.11.0