Re: [Lsf-pc] [LSF/MM/BPF TOPIC] time to reconsider tracepoints in the vfs?

Jan Kara
2025-01-16T17:29:38Z

On Thu 16-01-25 16:53:21, Al Viro wrote:
> On Thu, Jan 16, 2025 at 07:49:49AM -0500, Theodore Ts'o wrote:
>
> > Secondly, we've had a very long time to let the dentry interface
> > mature, and so (a) the fundamental architecture of the dcache hasn't
> > been changing as much in the past few years, and (b) we should have
> > enough understanding of the interface to understand where we could put
> > tracepoints (e.g., close to the syscall interface) which would make it
> > much less likely that there would be any need to make
> > backwards-incompatible changes to tracepoints.
>
> FWIW, earlier this week I'd been going through the piles of tracepoints
> playing with ->d_name. Mature interface or not, they do manage to
> fuck that up...

Well, tracepoints are like any other rarely executed kernel code. The bugs
do accumulate there with higher probability due to lack of testing. But I
guess that's not strong enough reason to refuse them.

I remember you were refusing tracepoints in VFS in the past on the grounds
that it could make code changes harder due to concerns of breaking
tracepoint users. That is a fair concern but I guess it is also a fair
question whether we shouldn't reconsider this decision given how the rest
of the Linux kernel and the tracing ecosystem around it evolves...

Honza

--
Jan Kara <jack@suse.com>
SUSE Labs, CR