From a83b3ec1d7ce2d656a4c476d65486371d1a659b2 Mon Sep 17 00:00:00 2001
From: Carlos Maiolino <cmaiolino@redhat.com>
Date: Tue, 2 May 2017 12:46:10 +0200
Subject: [PATCH] From 4f8f034a8969a48f210bf00be78a67cfb6964c72 Mon Sep 17
 00:00:00 2001 From: Carlos Maiolino
 <cmaiolino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Date: Thu, 20 Apr 2017
 14:53:01 +0200 Subject: [PATCH] make buffer size match kernel max transfer
 size

Currently libfuse has a hardcoded buffer limit to 128kib, while fuse
kernel module has a limit up to 32 pages.

This patch changes buffer limit to match the current page size, instead
of assuming 4096 bytes pages, enabling architectures with bigger pages
to use larger buffers, improving performance.

Also, add a new macro (HEADER_SIZE) to specify the space needed to
accommodate the header, making it easier to understand why those extra
4096 bytes are needed

Signed-off-by: Carlos Maiolino <cmaiolino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
---
 lib/fuse_kern_chan.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/fuse_kern_chan.c b/lib/fuse_kern_chan.c
index 5f77bbf..4cc9b73 100644
--- a/lib/fuse_kern_chan.c
+++ b/lib/fuse_kern_chan.c
@@ -80,7 +80,10 @@ static void fuse_kern_chan_destroy(struct fuse_chan *ch)
 		close(fd);
 }
 
-#define MIN_BUFSIZE 0x21000
+#define KERNEL_BUF_PAGES 32
+
+/* room needed in buffer to accommodate header */
+#define HEADER_SIZE 0x1000
 
 struct fuse_chan *fuse_kern_chan_new(int fd)
 {
@@ -89,7 +92,6 @@ struct fuse_chan *fuse_kern_chan_new(int fd)
 		.send = fuse_kern_chan_send,
 		.destroy = fuse_kern_chan_destroy,
 	};
-	size_t bufsize = getpagesize() + 0x1000;
-	bufsize = bufsize < MIN_BUFSIZE ? MIN_BUFSIZE : bufsize;
+	size_t bufsize = KERNEL_BUF_PAGES * getpagesize() + HEADER_SIZE;
 	return fuse_chan_new(&op, fd, bufsize, NULL);
 }
-- 
2.9.3