linux-kernel - Re: [PATCH] lib/vsprintf.c: increase the size of the field

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Date:	Thu, 10 Sep 2015 09:04:52 +0200
From:	Maurizio Lombardi <mlombard@...hat.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Joe Perches <joe@...ches.com>
Cc:	akpm@...ux-foundation.org, tj@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf.c: increase the size of the field_width
 variable

Hi Rasmus,

On 09/09/2015 08:51 PM, Rasmus Villemoes wrote:
> I'm also a little confused; I don't see what printk has to do with the
> reported problem (I'd expect the /sys/... file to be generated by
> something like seq_printf).

In the scsi-debug case scnprintf is used, but it doesn't really matter
because the change I made would influence printk and all its friends as
well... everything that will parse "%*pb[l]".

> 
>> %*pb is meant for smallish bitmaps, not big ones.
> 
> Yup. And that leads to my other confusion: Given that the expected
> output is given as "0-15", does the bitmap really consist of > S16_MAX
> bits with only the first 16 set?
> 

Yes. To be precise, in the example I mentioned in the commit message, a
bitmap of size = 524288 bits is created.
If you assign this number to a s16 variable the result will be zero and
nothing will be printed.

Joe, you mentioned that *pbl is meant for small bitmaps, what should I
use with big ones?

scsi-debug used the bitmap_scnlistprintf() function but since commit
dbc760bcc150cc27160f0131b15db76350df4334 this function is just a wrapper
around scnprintf("%*pbl");
as a consequence, the scsi-debug map_show() function stopped working
correctly.

Thanks,
Maurizio Lombardi
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