On 14.12.18 11:06, David Hildenbrand wrote:
> Looking at what the kernel does, looks like we should
> - Check for more errors
> - Try to execute !FORCED read if the FORCED one is unknown
> - Set the function code to a normal write
> - Set control_mask[2] to 0x80 (no idea what that means)
It's great that they set that and never actually check for its effects...
It's (drum roll):
SCLP_VARIABLE_LENGTH_RESPONSE
>
> The kernel seems to set the function code to 0x80. Looking at where that
> comes from, turns out this is a "dump indicator" to produce more
> meaningful dumps. Looking for other function codes used in the kernel, I
> discovered 0x40, which is used for "single increment assign" to speed up
> memory hotplug. I was not able to find out what "control_mask[2] = 0x80"
> means.
>
> I guess we can just set the funcion code to 0 ("normal write). Let's
> document the other bits in case anybody ever wonders what they mean.
> Also, let's just set the other bits in the mask to 0, not sure if they
> will actually be used, but this is definetly not wrong.
>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
I rebased my series on top of this patch and it works under LPAR:
Tested-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Please update the description, but apart from that:
Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
[...]
> +static void sclp_read_scp_info(ReadInfo *ri, int length)
> +{
> + unsigned int commands[] = { SCLP_CMDW_READ_SCP_INFO_FORCED,
> + SCLP_CMDW_READ_SCP_INFO };
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(commands); i++) {
> + ri->h.length = length;
> + ri->h.function_code = SCLP_FC_NORMAL_WRITE;
> + ri->h.control_mask[0] = 0;
> + ri->h.control_mask[1] = 0;
> + ri->h.control_mask[2] = 0x80;
We could test for the SCLP_RC_INSUFFICIENT_SCCB_LENGTH and redrive with
a longer response space because we set SCLP_VARIABLE_LENGTH_RESPONSE but
4k should be enough for tests. I do not expect this to be executed with
a few hundred VCPUs anyway.
> +
> + if (sclp_service_call(commands[i], ri))
> + break;
> + if (ri->h.response_code == SCLP_RC_NORMAL_READ_COMPLETION)
> + return;
> + if (ri->h.response_code != SCLP_RC_INVALID_SCLP_COMMAND)
> + break;
[...]
> diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h
> index 21d482b..131813e 100644
> --- a/lib/s390x/sclp.h
> +++ b/lib/s390x/sclp.h
> @@ -76,6 +76,8 @@
> #define SCLP_EVENT_BUFFER_ACCEPTED 0x80
>
> #define SCLP_FC_NORMAL_WRITE 0
> +#define SCLP_FC_SINGLE_INCREMENT_ASSIGN 0x40
> +#define SCLP_FC_DUMP_INDICATOR 0x80
If you want I could take that into my cleanups.
>
> typedef struct SCCBHeader {
> uint16_t length;
>
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