Re: compat_ioctl: unknown cmd on serial /dev/console

From: Arnd Bergmann
Date: Fri Jan 08 2010 - 11:18:31 EST

On Friday 08 January 2010, Atsushi Nemoto wrote:
> After the commit fb07a5f8 ("compat_ioctl: remove all VT ioctl
> handling"), I got this error message on 64-bit mips kernel with 32-bit
> busybox userland:
> ioctl32(init:1): Unknown cmd fd(0) cmd(00005600){t:'V';sz:0} arg(7fd76480) on /dev/console

Just to confirm: The behaviour of the kernel is still correct, it's only
the message you are worried about, right?

Sorry for this, it will be trivial to fix.

> The cmd 5600 is VT_OPENQRY. The busybox's init issues this ioctl to
> know vt-console or serial-console. If the console was serial console,
> VT ioctls are not handled by the serial driver.
> How this error should be fixed? Is this patch OK?
> diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
> index 332dd00..731478f 100644
> --- a/fs/compat_ioctl.c
> +++ b/fs/compat_ioctl.c
> #endif
> +/* Big V (for serial console case) */
> /* Little p (/dev/rtc, /dev/envctrl, etc.) */

I would probably write this as IGNORE_IOCTL() instead of COMPATIBLE_IOCTL
in order to document the intent, but it's functionally the same.

> And by quick search, I found some programs using VT_GETMODE to check
> vt-console is available or not. So VT_GETMODE might be an another
> candidate, but not sure.

Yes, that sounds reasonable, too.

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