Re: [PATCH v11 7/8] nbd: introduce ERRP_AUTO_PROPAGATE

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> If we want to add some info to errp (by error_prepend() or
> error_append_hint()), we must use the ERRP_AUTO_PROPAGATE macro.
> Otherwise, this info will not be added when errp == &error_fatal

Same for &error_abort, but to fix that, ERRP_AUTO_PROPAGATE() would have
to compromise stack backtraces, so it doesn't.

> (the program will exit prior to the error_append_hint() or
> error_prepend() call).  Fix such cases.

Unclear what exactly is being fixed here, if anything.  What are the
cases?  Can they happen?

The following look like possible cases: nbd_read(),
nbd_send_option_request(), nbd_handle_reply_err(), nbd_opt_info_or_go(),
nbd_start_negotiate(), nbd_receive_negotiate(),
nbd_negotiate_send_rep_verr(), nbd_negotiate_send_rep_list(),
nbd_negotiate_handle_export_name(), nbd_negotiate(),
nbd_export_remove().

Additionally in PATCH 6, v9fs_device_realize_common().

Nothing in PATCH 3+4+5+8 as far as I can tell.

If we lack the time to provide a complete assessment in the commit
messages, let's say so there.

> If we want to check error after errp-function call, we need to
> introduce local_err and then propagate it to errp. Instead, use
> ERRP_AUTO_PROPAGATE macro, benefits are:
> 1. No need of explicit error_propagate call
> 2. No need of explicit local_err variable: use errp directly
> 3. ERRP_AUTO_PROPAGATE leaves errp as is if it's not NULL or
>    &error_fatal, this means that we don't break error_abort
>    (we'll abort on error_set, not on error_propagate)

Direct use of @errp improves behavior when the argument is
&error_abort.  Worth mentioning, I think.

>
> This commit is generated by command
>
>     sed -n '/^Network Block Device (NBD)$/,/^$/{s/^F: //p}' \
>         MAINTAINERS | \
>     xargs git ls-files | grep '\.[hc]$' | \
>     xargs spatch \
>         --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
>         --macro-file scripts/cocci-macro-file.h \
>         --in-place --no-show-diff --max-width 80
>
> Reported-by: Kevin Wolf <kwolf@redhat.com>
> Reported-by: Greg Kurz <groug@kaod.org>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>