Re: [PATCH 1/2] mem-pool: add mem_pool_strfmt()

> On Sun, Feb 25, 2024 at 12:39:44PM +0100, René Scharfe wrote:
>
>> +static char *mem_pool_strvfmt(struct mem_pool *pool, const char *fmt,
>> +			      va_list ap)
>> +{
>> +	struct mp_block *block = pool->mp_block;
>> +	char *next_free = block ? block->next_free : NULL;
>> +	size_t available = block ? block->end - block->next_free : 0;
>> +	va_list cp;
>> +	int len, len2;
>> +	char *ret;
>> +
>> +	va_copy(cp, ap);
>> +	len = vsnprintf(next_free, available, fmt, cp);
>> +	va_end(cp);
>> +	if (len < 0)
>> +		BUG("your vsnprintf is broken (returned %d)", len);
>> +
>> +	ret = mem_pool_alloc(pool, len + 1);  /* 1 for NUL */
>> +
>> +	/* Shortcut; relies on mem_pool_alloc() not touching buffer contents. */
>> +	if (ret == next_free)
>> +		return ret;
>> +
>> +	len2 = vsnprintf(ret, len + 1, fmt, ap);
>> +	if (len2 != len)
>> +		BUG("your vsnprintf is broken (returns inconsistent lengths)");
>> +	return ret;
>> +}
>
> This is pulling heavily from strbuf_vaddf(). This might be a dumb idea,
> but... would it be reasonable to instead push a global flag that causes
> xmalloc() to use a memory pool instead of the regular heap?
>
> Then you could do something like:
>
>   push_mem_pool(pool);
>   str = xstrfmt("%.*s~%d^%d", ...etc...);
>   pop_mem_pool(pool);
>
> It's a little more involved at the caller, but it means that it now
> works for all allocations, not just this one string helper.