[PATCH] udevProcessCSS: fix segfault

[Erik Skultety]

On Mon, Sep 21, 2020 at 07:06:32PM +0200, Marc Hartmayer wrote:
> Don't process subchannel devices where `def->driver` is not set. This
> fixes the following segfault:
> 
> Thread 21 "nodedev-init" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x3ffb08fc910 (LWP 64303)]
> (gdb) bt
>  #0  0x000003fffd1272b4 in __strcmp_vx () at /lib64/libc.so.6
>  #1  0x000003ffc260c3a8 in udevProcessCSS (device=0x3ff9018d130, def=0x3ff90194a90)
>  #2  0x000003ffc260cb78 in udevGetDeviceDetails (device=0x3ff9018d130, def=0x3ff90194a90)
>  #3  0x000003ffc260d126 in udevAddOneDevice (device=0x3ff9018d130)
>  #4  0x000003ffc260d414 in udevProcessDeviceListEntry (udev=0x3ffa810d800, list_entry=0x3ff90001990)
>  #5  0x000003ffc260d638 in udevEnumerateDevices (udev=0x3ffa810d800)
>  #6  0x000003ffc260e08e in nodeStateInitializeEnumerate (opaque=0x3ffa810d800)
>  #7  0x000003fffdaa14b6 in virThreadHelper (data=0x3ffa810df00)
>  #8  0x000003fffc309ed6 in start_thread ()
>  #9  0x000003fffd185e66 in thread_start ()
> (gdb) p *def
> $2 = {
>   name = 0x0,
>   sysfs_path = 0x3ff90198e80 "/sys/devices/css0/0.0.ff40",

Okay, this patch fixes the segfault. However, if ^this generated it because the
driver name is not set, how do we even get to the resulting device tree as
outlined in 05e6cdafa6e0?

+- css_0_0_003a
    |
    +- ccw_0_0_1a2b
        |
        +- scsi_host0

What kind of CSS device is the one causing the error? If we skip this CSS
device, we don't generate a name for it and don't put it in the list, so I'm
quite puzzled on what I missed in the IBM document and thus in the review
process.

FWIW:
Reviewed-by: Erik Skultety <eskultet at redhat.com>