linux-kernel - [PATCH] virtio: console: Make resizing compliant with virtio spec

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Message-ID: <20250225092135.1200551-1-maxbr@linux.ibm.com>
Date: Tue, 25 Feb 2025 10:21:35 +0100
From: Maximilian Immanuel Brandtner <maxbr@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev
Cc: amit@...nel.org, arnd@...db.de, gregkh@...uxfoundation.org,
        brueckner@...ux.ibm.com, schnelle@...ux.ibm.com, pasic@...ux.ibm.com,
        maxbr@...ux.ibm.com
Subject: [PATCH] virtio: console: Make resizing compliant with virtio spec

According to the virtio spec[0] the virtio console resize struct defines
cols before rows. In the kernel implementation it is the other way around
resulting in the two properties being switched.
While QEMU doesn't currently support resizing consoles, TinyEMU
does[1](and they implement resizing according to the spec). CrosVM has
prototypes for virtio console resizing, but no user[2]. With the JSLinux
kernel[3] and alpine config[4] resizing the kernel works. It strongly
seems that they patch the issue downstream as patching their kernel to
use the upstream ordering breaks resizing.

[0] https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.pdf
[1] https://bellard.org/tinyemu/
[2] https://github.com/search?q=repo%3Agoogle/crosvm%20virtio_console_resize&type=code
[3] https://bellard.org/jslinux/kernel-x86.bin
[4] https://bellard.org/jslinux/alpine-x86.cfg

Fixes: 8345adbf96fc1 ("virtio: console: Accept console size along with resize control message")
Signed-off-by: Maximilian Immanuel Brandtner <maxbr@...ux.ibm.com>
Cc: stable@...r.kernel.org # v2.6.35+
---
 drivers/char/virtio_console.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 24442485e73e..9668e89873cf 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1579,8 +1579,8 @@ static void handle_control_message(struct virtio_device *vdev,
 		break;
 	case VIRTIO_CONSOLE_RESIZE: {
 		struct {
-			__u16 rows;
 			__u16 cols;
+			__u16 rows;
 		} size;
 
 		if (!is_console_port(port))
-- 
2.48.1