Re: [PATCH] bitmap: remove explicit newline handling using scnprintf format string

From: Sudeep Holla
Date: Mon Apr 27 2015 - 12:26:23 EST




On 27/04/15 17:14, Tejun Heo wrote:
Hello, Sudeep.

On Mon, Apr 27, 2015 at 10:46:58AM +0100, Sudeep Holla wrote:
int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
int nmaskbits)
{
- ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf - 2;
+ ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf;
int n = 0;

- if (len > 1) {
- n = list ? scnprintf(buf, len, "%*pbl", nmaskbits, maskp) :
- scnprintf(buf, len, "%*pb", nmaskbits, maskp);
- buf[n++] = '\n';
- buf[n] = '\0';
- }
+ if (len > 1)
+ n = list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) :
+ scnprintf(buf, len, "%*pb\n", nmaskbits, maskp);
return n;
}
EXPORT_SYMBOL(bitmap_print_to_pagebuf);

So, there's one behavior difference stemming from this. When the
buffer is too small, the original code would still output '\n' at the
end while the new code would just continue to print the formatted
string.

Completely agree and in-fact we did discuss that internally too.
But since this function deals only with page size buffers, we thought
it's highly unlikely to hit that corner case.

Given that bitmap outputs can be pretty long, this behavior
difference has a minute but still non-zero chance of causing something
surprising. There are multiple copies of the above function in arch
codes too.

I assumed that I had consolidated most of them in commit 5aaba36318e5
("cpumask: factor out show_cpumap into separate helper function").
I might have missed, will have a look at it again.

We prolly want to audit the usages to verify that the
passed in buffer is always big enough at which point the above
function and its copies can simply be replaced with direct scnprintf()
calls. This function doesn't actually add anything.


Ah, right that would be much simpler.

Regards,
Sudeep
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