[Libguestfs] [libnbd PATCH] generator: Trace return even when in wrong state
Richard W.M. Jones
rjones at redhat.com
Mon Aug 3 09:48:16 UTC 2020
On Fri, Jul 31, 2020 at 05:11:38PM -0500, Eric Blake wrote:
> Place the tracing of return values after any generated 'out:' label,
> as it is important to see even the errors caused by calling a function
> in the wrong handle state.
>
> Fixes: 9df088bfa9
> ---
>
> Multiple bugs found today, but only time to submit one patch so far.
> I found them all while trying to implement .list_exports in nbdkit.
>
> Bug 1: 'nbdinfo --list --json $uri' produces invalid JSON if there are
> 0 or more than 1 exports. We need to move the '"exports":[' and ']'
> into list_all_exports(), not list_one_export(), and manage correct
> trailing comma output. (We only tested nbdinfo with qemu-nbd, which
> only lists one export, explaining how we missed this)
>
> Bug 2: nbd_get_nr_list_exports() fails if the handle is still in READY
> state, even though there were exports listed and available in that
> case. I see no reason to forbid this during READY; but I've also
> mentioned that there are probably more changes coming to the way we do
> list export handling in libnbd to allow the reuse of a single handle
> rather than our current hacks of one handle per export. (We only
> tested nbdinfo with qemu-nbd, which generally does NOT allow
> NBD_OPT_GO on the '' export if it was advertising some other export;
> nbdkit is more forgiving, explaining why I hit a case where nbdinfo
> was calling this function in the wrong state)
>
> Bug 3: this patch. When a function fails due to use in the wrong
> state, the debug output was useless in telling me why.
>
> generator/C.ml | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/generator/C.ml b/generator/C.ml
> index 4a0b45d..2c62d4e 100644
> --- a/generator/C.ml
> +++ b/generator/C.ml
> @@ -542,13 +542,13 @@ let generate_lib_api_c () =
> pr " ret = nbd_unlocked_%s " name;
> print_arg_list ~wrap:true ~types:false ~handle:true args optargs;
> pr ";\n";
> - if may_set_error then (
> - pr "\n";
> - print_trace_leave ret;
> - pr "\n"
> - );
> + pr "\n";
> if !need_out_label then
> pr " out:\n";
> + if may_set_error then (
> + print_trace_leave ret;
> + pr "\n"
> + );
> if is_locked then (
> pr " if (h->public_state != get_next_state (h))\n";
> pr " h->public_state = get_next_state (h);\n";
ACK
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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