Stuff I do

Thrift Thrift is apache's tool. It can generate client / server codes based on a file written in it's own descriptor language. At first I was thrilled how easy it'll be to write a Cassandra client with it: "you just have to generate the C files, #include them, call a few functions and it's done". Yeah. Like anything in the world works like that. And this particular thing is no exception.

I had to write a kernel module recently that implemented a block device. I've carefully read the LDD3 material on every topic I thought might be useful; I concentrated mainly on block devices of course. Linux block drivers can do their job by providing a function that the kernel will call if it needs to do IO on the device. The first method described in LDD3 was the "request" method. According to this, the driver had to provide a function (wich was called the "request" function after the name of the field in a struct that is registered with the kernel at driver initialization). This function is called whenever a so-called request is available in a so-called request queue. The request does not equal to a single IO request that the kernel received from userspace (like when you do a read() on a disk for example). Such user space originating requests are merged and/or splitted to form suitably sized and appropriately queued chunks of IO to do.