[RFC] [PATCH] taskstats: introduce verison 9 with executable file info: empty device ID

[Dr. Thomas Orgis]

Hi,

this is a request for comments/help for a little patch I am working on.
It works to give me an inode for the executable file of an existing
task via taskstats, but I fail to get a device ID for that to be able
to then look for the correct filesystem in userspace. I am not sure if
that information is still supposed to be present at the time the stats
are produced. Basically, I want an efficient way to get the
path /proc/$pid/exe points to at process exit. I really would like to
not bother with individual tasks but only task groups (userspace
processes), but that seems to be tricky in taskstats, not being able to
tell a single-threaded process from a single thread of a multi-threaded
process â and also the tgid stats miss anything but the delay
accounting fields right now. My application in HPC just wants global
stats about wall-/cputime and memory use in a cluster, accounted for by
executable path, which encodes the used scientific software package and
version in our setup.

The one big hurdle I have at the moment is that I'm a n00b at kernel
development and just am taking gueses from the code I see. So far I
think I am accessing the correct struct member for the device ID, but
perhaps at the wrong time.

Also, I am open for suggestions for some better way of identifying the
executable. Instead of/in addition to the device ID, I would be
interested in the fsid (as given by `stat -c %i`) , for example. This
is stable for an NFS filesystem mounted on multiple nodes, where each
node has its own major:minor made up for the mount. But then, the
overlayfs for / on each netbooted node has a different fsid, while the
major:minor stays the same. So both would be good, I guess. Or a
filesystem UUID.

This is my commit/patch so far: