[PATCH] fbdevhw: fix sysfs path PCI device detection

[Thomas Zimmermann]

Hi

Am 15.07.24 um 12:21 schrieb Tj:
> Linux kernel v6.9 has changed the symlink to point to the parent device. This breaks fbdev_open() detection logic. Change it to use the subsystem symlink instead which will remain stable.
>
> Kernel v6.8:
>
> [    14.067] (II) fbdev_open() sysfs_path=/sys/class/graphics/fb0
> [    14.067] (II) fbdev_open() buf=../../devices/platform/vesa-framebuffer.0/graphics/fb0
>
> Kernel v6.9:
>
> [    15.609] (II) fbdev_open() sysfs_path=/sys/class/graphics/fb0
> [    15.609] (II) fbdev_open() buf=../../devices/pci0000:00/0000:00:01.0/vesa-framebuffer.0/graphics/fb0
>
> Originally found in automated Debian ISO QA testing [0] and confirmed in Linux [1].
>
> Tested on kernels v6.9.7 and v6.8.12
>
> [0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1075713
> [1] https://lore.kernel.org/lkml/lLyvPFC_APGHNfyGNHRpQy5izBikkaTPOpHooZIT3fFAoJPquSI31ZMueA99XTdr8ysir3X7O7IMdc6za-0m79vr_claeparHhoRouVgHOI=@proton.me/
>
> Fixes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1714
> Signed-off-by: Tj <tj.iam.tj at proton.me>

Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>

It might be more effective to open a merge request on 
https://gitlab.freedesktop.org/xorg/xserver

Best regards
Thomas

> ---
>   hw/xfree86/fbdevhw/fbdevhw.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/xfree86/fbdevhw/fbdevhw.c b/hw/xfree86/fbdevhw/fbdevhw.c
> index 76bc4809f..019af305b 100644
> --- a/hw/xfree86/fbdevhw/fbdevhw.c
> +++ b/hw/xfree86/fbdevhw/fbdevhw.c
> @@ -378,9 +378,9 @@ fbdev_open(int scrnIndex, const char *dev, char **namep)
>               node++;
>           }
>   
> -        if (asprintf(&sysfs_path, "/sys/class/graphics/%s", node) < 0 ||
> +        if (asprintf(&sysfs_path, "/sys/class/graphics/%s/device/subsystem", node) < 0 ||
>               readlink(sysfs_path, buf, sizeof(buf) - 1) < 0 ||
> -            strstr(buf, "devices/pci")) {
> +            strstr(buf, "bus/pci")) {
>               free(sysfs_path);
>               close(fd);
>               return -1;

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)