Tag owner bit in Request message

[chandu-tmba]

I am working on sending a request from the BMC, and I want to utilize my own tag rather than the tag generated by the kernel. For this request, I am using:

addrlen = sizeof(struct sockaddr_mctp_ext);
addr.smctp_base.smctp_family = AF_MCTP;
addr.smctp_base.smctp_network = MCTP_NET_ANY;
addr.smctp_base.smctp_type = MCTP_CTRL_TYPE;
addr.smctp_halen = I3C_PID_SIZE;
addr.smctp_ifindex = ifaceindex;
uint8_t tag = 0x05;
addr.smctp_base.smctp_tag = tag & MCTP_TAG_MASK;

Is this approach correct?

[jk-ozlabs]

Is this approach correct?

It will work, provided this is a non-owned tag (ie, TO is not set).

Given you're using a tag value of 0x05, this will send a message with the tag value of 0x05, which indicates a non-owned tag.

However, you also say:

I am working on sending a request from the BMC

If this is a request from the BMC, you will need the TO bit set, in which case your code is not correct.

[chandu-tmba]

thanks

[chandu-tmba]

@jk-ozlabs so if i want to create my own tag and send request with my own tag(i am the tag owner and i will set tag owner bit)

its not possible in existing mctp sockets ?

[jk-ozlabs]

You cannot specify your own tag if you need the TO bit set.

The kernel is responsible for owned-tag allocation, and the tag you specify may conflict with tags that the kernel has allocated. So, we do not permit arbitrary TO=1 tags to be specified here.

Can I ask why you're trying to use your own tag here?

[chandu-tmba]

i am trying to use libmctp , there tag handling is done by library

[jk-ozlabs]

You should not be using libmctp if you are using the Linux kernel MCTP implementation.

libmctp is intended for stand-alone environments - typically embedded - where the entire MCTP stack is implemented in the one library. This is not the case when using the Linux MCTP stack.