Re: [Qemu-devel] [PATCH 3/3] pc-bios/s390-ccw/net: Try to load pxelinux.cfg file accoring to the UUID

[Thomas Huth]

On 04.06.2018 11:36, Cornelia Huck wrote:
> On Wed, 30 May 2018 11:16:58 +0200
> Thomas Huth <address@hidden> wrote:
> 
>> With the STSI instruction, we can get the UUID of the current VM instance,
>> so we can support loading pxelinux config files via UUID in the file name,
>> too.
>>
>> Signed-off-by: Thomas Huth <address@hidden>
>> ---
>>  pc-bios/s390-ccw/netmain.c | 46 
>> +++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 45 insertions(+), 1 deletion(-)
>>
>> diff --git a/pc-bios/s390-ccw/netmain.c b/pc-bios/s390-ccw/netmain.c
>> index e84bb2b..7ece302 100644
>> --- a/pc-bios/s390-ccw/netmain.c
>> +++ b/pc-bios/s390-ccw/netmain.c
>> @@ -235,6 +235,49 @@ static void net_release(filename_ip_t *fn_ip)
>>  }
>>  
>>  /**
>> + * Retrieve the Universally Unique Identifier of the VM.
>> + * @return UUID string, or NULL in case of errors
>> + */
>> +static const char *get_uuid(void)
>> +{
>> +    register int r0 asm("0");
>> +    register int r1 asm("1");
>> +    uint8_t *mem, *buf, uuid[16];
>> +    int i, chk = 0;
>> +    static char uuid_str[37];
>> +
>> +    mem = malloc(2 * PAGE_SIZE);
>> +    if (!mem) {
>> +        puts("Out of memory ... can not get UUID.");
>> +        return NULL;
>> +    }
>> +    buf = (uint8_t *)(((uint64_t)mem + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1));
>> +    memset(buf, 0, PAGE_SIZE);
>> +
>> +    /* Get SYSIB 3.2.2 */
>> +    r0 = (3 << 28) | 2;
>> +    r1 = 2;
>> +    asm volatile(" stsi 0(%2)\n" : : "d" (r0), "d" (r1), "a" (buf)
>> +                 : "cc", "memory");
> 
> Maybe check for cc == 3 here, just to be safe? (We can probably assume
> a dbct >= 1 if it is successful, I think.)

Sure, I can add that check. In case it's not available, this should have
been catched by the "if (!chk)" below, but let's better be safe than
sorry here.

>> +
>> +    for (i = 0; i < 16; i++) {
>> +        uuid[i] = buf[8 * 4 + 12 * 4 + i];
> 
> Is there some way to make this offset less magic (offset of first vmdb
> + offset of uuid inside vmdb)?

Would a comment be sufficient? Or shall I copy the SysIB_322 structure
from target/s390x/cpu.h over to the s390-ccw bios?

 Thomas