linux-kernel - Re: [Lsf-pc] [LSF/MM/BPF TOPIC] tracing the source of errors

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Message-ID: <20240207110041.fwypjtzsgrcdhalv@quack3>
Date: Wed, 7 Feb 2024 12:00:41 +0100
From: Jan Kara <jack@...e.cz>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: lsf-pc <lsf-pc@...ts.linux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] tracing the source of errors

On Wed 07-02-24 10:54:34, Miklos Szeredi via Lsf-pc wrote:
> [I'm not planning to attend LSF this year, but I thought this topic
> might be of interest to those who will.]
> 
> The errno thing is really ancient and yet quite usable.  But when
> trying to find out where a particular EINVAL is coming from, that's
> often mission impossible.
> 
> Would it make sense to add infrastructure to allow tracing the source
> of errors?  E.g.
> 
> strace --errno-trace ls -l foo
> ...
> statx(AT_FDCWD, "foo", ...) = -1 ENOENT [fs/namei.c:1852]
> ...
> 
> Don't know about others, but this issue comes up quite often for me.

Yes, having this available would be really useful at times. Sometimes I
had to resort to kprobes or good old printks.

> I would implement this with macros that record the place where a
> particular error has originated, and some way to query the last one
> (which wouldn't be 100% accurate, but good enough I guess).

The problem always has been how to implement this functionality in a
transparent way so the code does not become a mess. So if you have some
idea, I'd say go for it :)

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