On 11/17/2016 11:12 PM, Jarkko Sakkinen wrote: > On Thu, Nov 17, 2016 at 05:20:36PM +0530, Nayna wrote: > >> I tested this for capability TPM2_CAP_PCRS. It seems TPM2_CAP_PCRS >> capability always returns full PCR allocation, and more_data as 0, So, I >> think the idea of looping over based on more_data may not work for this >> capability. > > You can always request one value at a time until there's no more. > > If you request N values, depending on the hardware, the hardware returns > to you anything from 1 to N values. If you implement a function that > requests N values in the command, you *must* handle the case where > moreData is 1 even if the hardware you are testing that never happens. > > That's the reason why I would start with a function that you request one > property of one capability and optimize it in future if it doesn't scale > for some workload. > > Do you have a workload where it doesn't scale?
Thanks Jarkko for explaining in detail. If I understood correctly, the idea is to request for one property at a time, and if we need multiple properties, then to request for each of them in a loop. In case of TPM2_CAP_PCRS, property is always zero. This is how I am calling getcap_cmd for TPM2_CAP_PCRS. tpm2_getcap_cmd(chip, TPM2_CAP_PCRS, 0, &cap_data, "get active pcr banks"); Output : [ 17.081665] tpm: cap id to receive value is 2 [ 17.081666] tpm: TPM2_CAP_COMMANDS: more data 1 [ 17.081667] tpm: 2 [ 17.081668] tpm: tpm2_get_active_banks -------> cap is TPM2_CAP_PCRS [ 17.171665] tpm: cap id to receive value is 5 [ 17.171666] tpm: TPM2_CAP_PCRS: more data 0 ---> more data is zero. [ 17.171666] tpm: TPM2_CAP_PCRS: more data 0 [ 17.171667] tpm: count pcr banks is 2 ------> count of active pcr banks information returned more_data is always zero here, so am not sure how to handle more_data in this case ? Since property_id is always zero, I am not able to request for one property at a time. and response_buffer returns the details for both active banks. This is the expected behavior defined in TCG 2.0 Part 3 Commands Specification (Section 30.2.1): "TPM_CAP_PCRS – Returns the current allocation of PCR in a TPML_PCR_SELECTION. The property parameter shall be zero. The TPM will always respond to this command with the full PCR allocation and moreData will be NO." Please let me know, if I am missing something. Thanks & Regards, - Nayna > > /Jarkko > ------------------------------------------------------------------------------ _______________________________________________ tpmdd-devel mailing list tpmdd-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/tpmdd-devel