linux-kernel - [PATCH v5 1/4] fuse: reserve byteswapped init opcodes

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Message-Id: <20190910151206.4671-2-mszeredi@redhat.com>
Date:   Tue, 10 Sep 2019 17:12:03 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: [PATCH v5 1/4] fuse: reserve byteswapped init opcodes

From: "Michael S. Tsirkin" <mst@...hat.com>

virtio fs tunnels fuse over a virtio channel.  One issue is two sides might
be speaking different endian-ness. To detects this, host side looks at the
opcode value in the FUSE_INIT command.  Works fine at the moment but might
fail if a future version of fuse will use such an opcode for
initialization.  Let's reserve this opcode so we remember and don't do
this.

Same for CUSE_INIT.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 include/uapi/linux/fuse.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 2971d29a42e4..df2e12fb3381 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -425,6 +425,10 @@ enum fuse_opcode {
 
 	/* CUSE specific operations */
 	CUSE_INIT		= 4096,
+
+	/* Reserved opcodes: helpful to detect structure endian-ness */
+	CUSE_INIT_BSWAP_RESERVED	= 1048576,	/* CUSE_INIT << 8 */
+	FUSE_INIT_BSWAP_RESERVED	= 436207616,	/* FUSE_INIT << 24 */
 };
 
 enum fuse_notify_code {
-- 
2.21.0