Re: [Libguestfs] [PATCH miniexpect 2/2] Add debugging capability at runtime.
On 10/12/2017 09:12 AM, Pino Toscano wrote:
On Wednesday, 11 October 2017 17:23:45 CEST Richard W.M. Jones
wrote:
> +static int
> +mexp_vprintf (mexp_h *h, int password, const char *fs, va_list args)
> {
> - va_list args;
> char *msg;
> int len;
> size_t n;
> ssize_t r;
> char *p;
>
> - va_start (args, fs);
> len = vasprintf (&msg, fs, args);
> - va_end (args);
Due to the nature of va_list (whose implementation greatly differs per
architecture -- from a pointer, to a list of pointers, to structs, etc),
I think that here you need to copy the va_list using va_copy(), and
pass the copy to vasprintf.
Not needed here. If you take va_list as a parameter and do nothing
further with it other than to forward on to another function that takes
va_list, you are fine.
If you use va_list* anywhere, or if you want to do partial processing on
args before handing the rest of args to another function, then you are
indeed correct that a va_copy makes life easier.
I cannot find a better reference, but
https://stackoverflow.com/questions/3369588/pass-va-list-or-pointer-to-va...
has a piece of advice on that.
Here's a recent explanation on the qemu list, where va_list* is
involved, and thus the va_copy is necessary:
https://lists.gnu.org/archive/html/qemu-devel/2017-10/msg00171.html
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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