About Adam Young

Once upon a time I was an Army Officer, but that was long ago. Now I work as a Software Engineer. I climb rocks, play saxophone, and spend way too much time in front of a computer.

Opening the perf file descriptor

A couple months back I recorded this line on my blog as part of investigating perf:

perf record --branch-filter any,save_type,u true 

What is the interface between the perf binary and the linux Kernel when I run this? There is a system call to open a file handle. The man page says this:

int syscall(SYS_perf_event_open, struct perf_event_attr *attr,
                    pid_t pid, int cpu, int group_fd, 
                    unsigned long flags);

But how does that get called by the perf binary…the answer is trickier than I originally thought.

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Testing an MCTP Driver via Echo request

MCTP stands for Management Component Transport Protocol. While it is designed around a server, it is also designed as a network protocol. As such, the Linux implementation makes use of the Socket interface and the Kernel plumbing for dealing with network protocols. To support a new transport mechanism, you implement a new device driver specific to that transport mechanism that implements the struct net_device contract, which includes implementing the functions for struct net_device_ops.

Before I write a full implementation, I want to write something that only echos a packet back to the receiver. This mimics the behavior of the mctp-echo server in the user tools, and can make use of the mctp-req echo client.

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Remote git with ssh

Working on a different architecture from my Laptop means that I am invariably working on a remote machine. My current development can be done on an Ampere AltraMax machine, which means I have 80 processors available; quite a nice benefit when doing a Linux Kernel compile that can use all of the processors available.

Because the machine is a shared resource out of out lab, I want to make sure I can recreate my work there on another machine; this one could be reclaimed or powered down due to lab priorities. Thus, all my remote work is done in git, and I use the ssh protocol to pull changes from my work server to my laptop fairly regularly…whenever I feel I have valuable work that could be potentially lost.

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Acronym Challenge Programmatic Interface

How do you know what is inside your computer? There are a couple tools. If the hardware is on the PCI bus, from the command line you can run lspci, which will in turn enumerate the discovered devices on that bus. But what if the hardware is not on the PCI bus? And how does the Kernel discover it in the first place? For the hardware that I have to work with, the answer is that it is enumerated by the Unified Extensible Firmware Interface (UEFI) coded embedded in the device and exposed via the Advanced Configuration and Power Interface (ACPI). This world is full of four letter acronyms. Here are my notes on some of them.

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