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Date: Wed, 10 Jan 2024 18:08:23 -0500
From: Rafael Aquini <aquini@redhat.com>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Audra Mitchell <audra@redhat.com>, linux-kernel@vger.kernel.org,
	tj@kernel.org, jiangshanlai@gmail.com,
	hirokazu.yamauchi.hk@hitachi.com, ddouwsma@redhat.com,
	loberman@redhat.com, raquini@redhat.com
Subject: Re: [PATCH v2] workqueue.c: Increase workqueue name length
Message-ID: <ZZ8jZ3J63jf4Ap3y@optiplex-fbsd>
References: <20231215193954.1785069-1-audra@redhat.com>
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On Wed, Jan 10, 2024 at 11:52:38PM +0100, Rasmus Villemoes wrote:
> On 10/01/2024 23.31, Rafael Aquini wrote:
> > On Wed, Jan 10, 2024 at 11:06:22PM +0100, Rasmus Villemoes wrote:
> >> On 10/01/2024 22.52, Rafael Aquini wrote:
> 
> >>> The extra vsnprintf call is required because the return of the existing 
> >>> vsnprintf() is going to be already capped by sizeof(wq->name).
> >>
> >> No, it is not. vsnprintf() returns the length of the would-be-created
> >> string if the buffer was big enough. That is independent of whether one
> >> does a dummy NULL,0 call or just calls it with a real, but possibly too
> >> small, buffer.
> >>
> >> This is true for userspace (as required by posix) as well as the kernel
> >> implementation of vsnprintf(). What makes you think otherwise?
> >>
> > 
> > this snippet from PRINTF(3) man page
> > 
> > RETURN VALUE
> >        Upon successful return, these functions return the number of characters 
> >        printed (excluding the null byte used to end output to strings).
> > 
> 
> Assuming we have the same man pages installed, try reading the very next
> paragraph:
> 
>  The functions snprintf() and vsnprintf() do not write  more  than  size
>  bytes  (including the terminating null byte ('\0')).  If the output was
>  truncated due to this limit, then the return value  is  the  number  of
>  characters  (excluding the terminating null byte) which would have been
>  written to the final string if enough space had been available.   Thus,
>  a  return  value  of  size or more means that the output was truncated.
> 
> How else would you even expect the vsnprintf(NULL, 0, ...) thing to work?
>

OK, that's my bad! Sorry for the noise.
-- Rafael