At the Kernel Summit in Prague last week Kay Sievers and I lead a session on developing shared userspace libraries, for kernel hackers. More and more userspace interfaces of the kernel (for example many which deal with storage, audio, resource management, security, file systems or a number of other subsystems) nowadays rely on a dedicated userspace component. As people who work primarily in the plumbing layer of the Linux OS we noticed over and over again that these libraries written by people who usually are at home on the kernel side of things make the same mistakes repeatedly, thus making life for the users of the libraries unnecessarily difficult. In our session we tried to point out a number of these things, and in particular places where the usual kernel hacking style translates badly into userspace shared library hacking. Our hope is that maybe a few kernel developers have a look at our list of recommendations and consider the points we are raising.
To make things easy we have put together an example skeleton library we dubbed libabc, whose README file includes all our points in terse form. It's available on kernel.org:
This list of recommendations draws inspiration from David Zeuthen's and Ulrich Drepper's well known papers on the topic of writing shared libraries. In the README linked above we try to distill this wealth of information into a terse list of recommendations, with a couple of additions and with a strict focus on a kernel hacker background.
Please have a look, and even if you are not a kernel hacker there might be something useful to know in it, especially if you work on the lower layers of our stack.
If you have any questions or additions, just ping us, or comment below!