[PATCH procd] utils: fix get_active_console when kernel returns multiple values

[Daniel Golle]

Hi Mathew,

On Tue, Jan 25, 2022 at 03:12:08AM +0000, Mathew McBride wrote:
> /sys/class/tty/console/active may return multiple values on
> kernels where framebuffer support is enabled but the system
> is supposed to be using a serial console.
> e.g
> $ cat /sys/class/tty/console/active
> tty0 ttyS0

On BPi-R2 (which got HDMI with console) I'm seeing this:
root at OpenWrt:~# cat /sys/class/tty/console/active
ttyS2 tty1

And I suspect it will be the same at least for

linux/tegra/image/generic-bootscript:setenv bootargs "root=PARTUUID=${ptuuid} rw rootwait console=ttyS0,115200 console=tty0"
linux/bcm27xx/image/cmdline.txt:console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=squashfs,ext4 rootwait
linux/rockchip/image/mmc.bootscript:setenv bootargs "console=ttyS2,1500000 console=tty1 earlycon=uart8250,mmio32,0xff1a0000 root=PARTUUID=${uuid} rw rootwait"

as the order of console in that sysfs file apparently corresponds to
the order of console= arguments passed via kernel cmdline.

bcm27xx, mt7623 and tegra enable the frame-buffer console via inittab,
while rockchip doesn't ship /etc/inittab.

> 
> On such systems, tty0 is a dummy console:
> [    0.008273] Console: colour dummy device 80x25
> [    0.012742] printk: console [tty0] enabled
> 
> The serial console doesn't appear until much later:
> [    0.092468] 21c0500.serial: ttyS0 at MMIO 0x21c0500
> [    1.713893] printk: console [ttyS0] enabled
> 
> So far this only appears to happen on systems using
> device tree.
> 
> In these circumstances, use the last console device
> shown in the sysfs active file.

While I agree that we need to somehow unify and solve this, just
changing the current behavior will break serial console access at least
on the targets listed above.

So either you should suggest to change the affected target to ship
/etc/inittab or supply console= kernel parameter, or we change all the
other targets above (and maybe more where console= parameter originates
from existing non-OpenWrt-built bootchain).

Does our current behaviour (using first active console) violate any
universal convention we should obey?


Cheers


Daniel

> 
> Fixes: 2cfc26f ("inittab: detect active console from kernel if no console= specified")
> Signed-off-by: Mathew McBride <matt at traverse.com.au>
> ---
>  utils/utils.c | 25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/utils/utils.c b/utils/utils.c
> index f0c4a90..43b24c6 100644
> --- a/utils/utils.c
> +++ b/utils/utils.c
> @@ -138,6 +138,10 @@ blobmsg_list_equal(struct blobmsg_list *l1, struct blobmsg_list *l2)
>  char *get_active_console(char *out, int len)
>  {
>  	char line[CMDLINE_SIZE + 1];
> +	char *sptr, *token;
> +	char *console = NULL;
> +
> +	memset(line, 0, sizeof(line));
>  	int fd = open("/sys/class/tty/console/active", O_RDONLY);
>  	ssize_t r;
>  
> @@ -152,15 +156,22 @@ char *get_active_console(char *out, int len)
>  	if (r <= 0)
>  		return NULL;
>  
> -	/* The active file is terminated by a newline which we need to strip */
> -	char *newline = strtok(line, "\n");
> -
> -	if (newline != NULL) {
> -		strncpy(out, newline, len);
> -		return out;
> +	/* There may be multiple 'active' consoles.
> +	 * On kernels that support both graphical and
> +	 * serial consoles, Linux may create a 'dummy'
> +	 * framebuffer console on tty0 if no other console
> +	 * device has been probed yet. Often a serial
> +	 * driver (e.g ttyS0) might only be probed later
> +	 * in the boot process.
> +	 */
> +	for (token = strtok_r(line, " \t\n", &sptr); token;
> +	     token = strtok_r(NULL, " \t\n", &sptr)) {
> +		strncpy(out, token, len);
> +		console = out;
>  	}
> +	out[len-1] = '\0';
>  
> -	return NULL;
> +	return console;
>  }
>  
>  char* get_cmdline_val(const char* name, char* out, int len)
> -- 
> 2.30.1
> 
> 
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