Stacking Protocols

Posted on by
Reply

I find myself writing a program in C that is supposed to handle multiple protocols. At its entry point, the protocol is Platform Communication Channel (extended memory, type 3 and type 4). Embedded in that is an Management Component Transport Protocol (MCTP) message, and embedded in that is one of many different protocols.

I might want to swap out the PCC layer in the future for….something else. MCTP can come over many different protocols, so there is a good be that the tool will be more useful if it can assume that the protocol outside of the MCTP layer is something other than MCTP.

One problem I have is that the MCTP header does not have a length field. We do not not know how long the payload is; all it has is version, source, destination, and flags. Thus, if we want to pass a buffer of type MCTP header along, and we want the length, we need to pass it in a separate field. This goes both for incoming (how many bytes to read) and outgoing (how many bytes to write).

Continue reading →

Install a custom Kernel inside a VM

Posted on by
Reply

When debugging Qemu, it might be helpoful to instrument Linux Kernel to see when interrupts get received, or see data on the other side of a transfer. If you have to modify the Kernel on a regular basis, it can be faster to build it in place than to build a customer RPM/DEB and install inside the VM. Here is how I have been going about updating the kernel.

Continue reading →

Viewing the Flattened Device Tree from Qemu

Posted on by
Reply

The Qemu implementation uses a Flattened Device Tree (FTD) to manage the virtual implementation of the physical devices in a machine. I need to create a FTD entry for the MCTP-PCC implementation I am writing in Qemu. Since this is new to me, and I am working (as I most often do) via Ttrial and error, I want to see the FTD entry after I write it. Here is how I am dumping it.

Continue reading →

Debugging Qemu with gdb

Posted on by
Reply

When developing Linux Kernel code, I have found myself wanting to have a test fixture inside the Firmware that lets me inspect the values communicated out of and into the Linux Kernel. I am currently writing one such fixture in Qemu. And I have an interrupt that is not getting handled by the Linux Kernel, I think because it is not getting delivered.

I have found it quite valuable to run this Qemu process in the Gnu Debugger. Here is how I (with help) got to the bottom of the mystery.

Continue reading →

Self hosting and installing from pip repos

Posted on by
Reply

I have an application that I want to share with my team. Fortunately, we have a shared server, so it is pretty easy to do so: if I put a file in /usr/local/bin it can A) be executed by anyone on the server and B) will not interfere with RPM packages. But, I do potentially want to put this code on other machines as well, so I am going to buld it as a pip package, upload it to a team repo (apache HTTPD instance on this machine) and then install it from pip as root.

Continue reading →

Tools First

Posted on by
Reply

I have wasted a lot of time as a developer waiting for long running processes to complete. Whether it is a Linux Kernel compile, and Ansible Playbook tearing down and recreating a system on a remote server, or a gitlab pipeline building and testing code, the common problem is that my head is in the problem being addressed there, but I cannot do anything to verify hypotheses until the process completes. I often get distracted while waiting, and find that what could have been a 5 minute turn around has become a 2 hour turn around.

Continue reading →