Re: [PATCH 4/5] test_printf: Append '|' more efficiently

[Rasmus Villemoes <linux@rasmusvillemoes.dk>]

On 13/10/2021 07.22, Yafang Shao wrote:
> On Wed, Oct 13, 2021 at 2:33 AM Matthew Wilcox (Oracle)
> <willy@infradead.org> wrote:
>>
>> Instead of calling snprintf(), just append '|' by hand.
>>
>> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>> ---
>>  lib/test_printf.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/test_printf.c b/lib/test_printf.c
>> index 60cdf4ba991e..662c3785aa57 100644
>> --- a/lib/test_printf.c
>> +++ b/lib/test_printf.c
>> @@ -623,9 +623,9 @@ page_flags_test(int section, int node, int zone, int last_cpupid,
>>                 if (!pft[i].width)
>>                         continue;
>>
>> -               if (append) {
>> -                       snprintf(cmp_buf + size, BUF_SIZE - size, "|");
>> -                       size = strlen(cmp_buf);
>> +               if (append && size < BUF_SIZE) {
> 
> Should it be:
>                     if (append && size < BUF_SIZE - 1)
> ?
> 

Perhaps, but the whole thing screams "don't do it like this". We have
seq_buf to abstract a "buffer with known length you can do a bunch of
snprintfs to". That's what should be used. Then the test can also error
out if seq_buf_has_overflowed(), because that's a bug in the test.

Alternatively, the right pattern is "size += scnprintf(cmp_buf + size,
BUF_SIZE - size)", since that will eventually saturate size at BUF_SIZE-1.

Rasmus