patch 1/2 debuginfod client

Frank Ch. Eigler fche@redhat.com
Mon Nov 18 20:33:00 GMT 2019


Hi -

> > > But since the user won't see the URL generated they might not notice
> > > what is really going on. They will just see that something wasn't
> > > found, won't they?
> > 
> > Yes, so the only benefit would be the generation of a different error
> > message for impossible buildids.
> 
> But if there are multiple server URLs it might not be clear which/where
> the error came from. 

(My comment was about detecting even number of chars in the hex code.)

> Since all this is done through a very simple web
> api I think it is useful for the user to get informed about what the
> actual request URL was that failed. [...]
> If we go with the client connection context idea for the API we could
> add an extra function that would tell you the last URL tried maybe?

Yeah, maybe.  They are tried in parallel.  We could also hook up to
libcurl's own progress-notification callbacks.


> > > Do you know how other libraries that use libcurl deal with this?
> > 
> > I looked over some other libcurl users in fedora.  Some don't worry
> > about the issue at all, relying on implicit initialization, which is
> > only safe if single-threaded.  Others (libvirtd) do an explicitly
> > invoked initialization function, which is also only safe if invoked
> > from a single-threaded context.
> > 
> > I think actually our way here, running the init function from the
> > shared library constructor, is about the best possible.  As long as
> > the ld.so process is done as normal, it should be fine.  Programs that
> > use the elfutils trick of manual dlopen'ing libdebuginfod.so should do
> > so only if they are single-threaded.
> 
> But they cannot really control that... Since they might not know (and
> really shouldn't care) that libdw lazily tries to dlopen
> libdebuginfod.so which then pulls in libcurl and calls that global init
> function...
> 
> Could we do try to do the dlopen and global curl initialization from
> libdw _init, or a ctor, to make sure it is done as early as possible? 

Doing a redundant initialization later is not a problem; there is a
counter in there.  The problematic case would be
- a multithreaded application
- loading debuginfod.so multiply concurrently somehow
- and calling the solib ctor concurrently somehow
- and all of this concurrently enough to defeat libcurl's init-counter

IMHO, not worth worrying about.  Someday libcurl will do the right
thing (tm) and plop this initialization into their solib ctor.

> > > I was more thinking zero == infinity (no timeout).
> > 
> > An unset environment variable should do that.
> 
> Are you sure? If DEBUGINFOD_TIMEOUT isn't set, then it seems it
> defaults to 5 seconds:
> 
> /* Timeout for debuginfods, in seconds.
>    This env var must be set for debuginfod-client to run.  */
> static const char *server_timeout_envvar = DEBUGINFOD_TIMEOUT_ENV_VAR;
> static int server_timeout = 5;
> [...]
> 
>   if (getenv(server_timeout_envvar))
>     server_timeout = atoi (getenv(server_timeout_envvar));

OK, hm, we could make an -empty- but set environment variable mean
'infinity'.  Then again, a user can also say =99999.

- FChE



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