linux-kernel - Re: [PATCH] virtio: console: Make resize control event handling compliant with spec

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Message-ID: <20250323134010.30ea007d.pasic@linux.ibm.com>
Date: Sun, 23 Mar 2025 13:40:10 +0100
From: Halil Pasic <pasic@...ux.ibm.com>
To: Maximilian Immanuel Brandtner <maxbr@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
        mst@...hat.com, amit@...nel.org, schnelle@...ux.ibm.com,
        Halil Pasic
 <pasic@...ux.ibm.com>
Subject: Re: [PATCH] virtio: console: Make resize control event handling
 compliant with spec

On Thu, 20 Mar 2025 18:26:54 +0100
Maximilian Immanuel Brandtner <maxbr@...ux.ibm.com> wrote:

Let my try to do some nitpicking here. First on the subject. I would go
with something more specific like "fix order of fields cols and rows",
especially now that we have figured out the byte order handling is absent
as well.

> According to section 5.3.6.2 of the virtio spec a control buffer with

I would refrain form referencing section from the spec only by its
number without also telling which incarnation of the spec you mean. I
don't think those numbers are set in stone.

> the event VIRITO_CONSOLE_RESIZE is followed by a virtio_console_resize
> struct containing 2 little endian 16bit integerts cols,rows. 

s/integerts/integers/

I think technically it is still the same buffer. I would opt for struct
virtio_console_control is followed by struct virtio_console_resize. 

> The kernel
> implementation assums native endianness (which results in mangled
> values on big endian architectures)(a seperate patch by Halil Pasic
> will deal with that issue) and swaps the ordering of columns and rows.

I would simply omit the reference to the other patch. I understand that
you introduced this because your patch does not deliver everything that
the short description promises.

I didn't realize that addressing the byte order stuff would cause
a merge conflict, but it does. So maybe it would make sense to rebase
your fix on top of mine and send it as a series titled.
"Make resize control event handling compliant with spec". Just an idea.

> This patch changes the ordering of rows and columns to columns then
> rows.
> 
> 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))