netdev - Re: [patch iproute2-next v3 3/6] devlink: extend pr_out_nested

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Date: Fri, 27 Oct 2023 11:16:41 -0600
From: David Ahern <dsahern@...il.com>
To: Petr Machata <me@...chata.org>
Cc: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
 stephen@...workplumber.org, daniel.machon@...rochip.com
Subject: Re: [patch iproute2-next v3 3/6] devlink: extend
 pr_out_nested_handle() to print object

On 10/27/23 7:12 AM, Petr Machata wrote:
> I was wondering whether somehing like this might make sense in the
> iproute2 library:
> 
> 	#define alloca_sprintf(FMT, ...) ({					\
> 		int xasprintf_n = snprintf(NULL, 0, (FMT), __VA_ARGS__);	\
> 		char *xasprintf_buf = alloca(xasprintf_n);			\
> 		sprintf(xasprintf_buf, (FMT), __VA_ARGS__);			\
> 		xasprintf_buf;							\
> 	})
> 
> 	void foo() {
> 		const char *buf = alloca_sprintf("%x %y %z", etc.);
> 		printf(... buf ...);
> 	}
> 
> I'm not really happy with it -- because of alloca vs. array, and because
> of the double evaluation. But all those SPRINT_BUF's peppered everywhere
> make me uneasy every time I read or write them.

agreed.

> 
> Or maybe roll something custom asprintf-like that can reuse and/or
> realloc a passed-in buffer?
> 
> The sprintf story is pretty bad in iproute2 right now, IMHO.

It is a bit of a mess. If you have a few cycles, want to send an RFC?
Just pick 1 or 2 to convert to show intent with a new design.