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Date:   Fri, 21 Jul 2023 15:45:30 -0700
From:   lars@pixar.com
To:     linux-nfs@vger.kernel.org
Subject: Best kernel function to probe for NFS write accounting?
Message-ID: <20230721224530.I6e45%lars@pixar.com>
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Hello,

I'm using BPF to do NFS operation accounting for user-space processes. I'd like
to include the number of bytes read and written to each file any processes open
over NFS.

For write operations, I'm currently using an fexit probe on the
nfs_writeback_done function, and my program appears to be getting the
information I'm hoping for. But I can see that under some circumstances the
actual operations are being done by kworker threads, and so the PID reported by
the BPF program is for that kworker instead of the user-space process that
requested the write.

Is there a more appropriate function to probe for this information if I only
want it triggered in context of the user-space process that performed the
write? If not, I'm wondering if there's enough information in a probe triggered
in the kworker context to track down the user-space PID that initiated the
writes.

I didn't find anything related in the kernel's Documentation directory, and I'm
not yet proficient enough with the vfs, nfs, and sunrpc code to find an
appropriate function myself.

If it matters, our infrastructure is all based on NFSv3.

Thanks for any leads or documentation pointers!
Lars