GSoC Idea: per-process filesystem namespaces for FreeBSD

[Theron]

Hello All,

I am an undergraduate a Boston University looking to contribute to 
FreeBSD this summer under GSoC.

The idea I would like to implement is to bring to FreeBSD a per-process 
mounting / namespaces functionality similar to that of the Plan9 
operating system as a means to give greater flexibility in combination 
with less overhead than is associated with chroots and jails for 
purposes of isolating software setups from one another and from the 
underlying system.

For those unfamiliar with Plan9, here is a rough explanation of the 
namespace feature: unlike in Unix, where all processes share the same 
virtual filesystem, each process instead has its own view of the 
filesystem according to what has been mounted, which, unlike Unix mount, 
as an unpriviliged operation changing only what is seen by the 
particular process and any processes it later spawns.  Thus it is 
possible for one process's /bin to be completely different from another 
process's /bin, and neither need be the same as the system's /bin, 
should one exist.

As an example of its application and potential usefulness, a user may 
mount on top of /usr/local an overlay pointing to a location owned by 
the user, allowing existing binary packages which expect a /usr/local 
PREFIX to be installed and run without any modification either to the 
binary packages or to the underlying system.  Currently the only ways to 
achieve this are by recompiling ports with a different PREFIX or by 
configuring a jail.  Some, but not all, programs will function 
out-of-place under tweaked PATH and LD_LIBRARY_PATH, but this is not a 
general solution and leads to messy environments.

Although I have not previously worked with kernel programming in 
particular, I have good experience of high-level practices and low-level 
details of C programming and I can teach myself new technical details 
quickly.  In researching how to approach the task, I will study the 
existing implementation of chroot, jail, and fdescfs as examples of 
process-specific namespace behavior already supported in FreeBSD 
kernel.  The nullfs and unionfs may also serve as work to build off of, 
although unionfs as currently implemented appears to be partially broken.

Robustness of the implementation allowing, it should eventually be 
possible to replace system directories /bin, /sbin, /etc, etc. with 
bindings configured at boot time to improve the safety of live system 
upgrades and to provide a means of returning to older configurations 
which is not dependent on filesystem-specific snapshotting features.

Although per-process filesystem namespacing is unconventional in the 
face of the dominant Unix single-namespace model, introducing the 
feature to a Unix-like system does not constitute a radical change, as 
it is compatible with and indeed facilitates the meeting of the 
reasonable expectation of existing and unmodified software to find 
resources in predetermined file paths.

My attempt here to outline the relevant concepts is to the best of my 
limited understanding.  Hopefully I am not creating or propagating any 
misinformation and have not grossly misassessed the complexity of the task.

I would greatly appreciate any suggestions of approaches to this task 
and of who to contact for more expertise and for potential mentorship.

Thanks,
Theron Tarigo