netdev - Re: [PATCH net-next] octeontx2-pf: Treat truncation of IRQ name as an error

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Message-ID: <aa0246ef-5696-42ea-9f00-4815d268abb7@lunn.ch>
Date: Wed, 1 May 2024 22:21:30 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Simon Horman <horms@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Sunil Goutham <sgoutham@...vell.com>,
	Geethasowjanya Akula <gakula@...vell.com>,
	Subbaraya Sundeep <sbhatta@...vell.com>,
	Hariprasad Kelam <hkelam@...vell.com>,
	Dan Carpenter <dan.carpenter@...aro.org>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] octeontx2-pf: Treat truncation of IRQ name as
 an error

On Wed, May 01, 2024 at 09:11:46PM +0100, Simon Horman wrote:
> On Wed, May 01, 2024 at 09:46:15PM +0200, Andrew Lunn wrote:
> > On Wed, May 01, 2024 at 07:27:09PM +0100, Simon Horman wrote:
> > > According to GCC, the constriction of irq_name in otx2_open()
> > > may, theoretically, be truncated.
> > > 
> > > This patch takes the approach of treating such a situation as an error
> > > which it detects by making use of the return value of snprintf, which is
> > > the total number of bytes, including the trailing '\0', that would have
> > > been written.
> > > +		name_len = snprintf(irq_name, NAME_SIZE, "%s-rxtx-%d",
> > > +				    pf->netdev->name, qidx);
> > > +		if (name_len >= NAME_SIZE) {
> > 
> > You say name_len includes the trailing \0. So you should be able to
> > get NAME_SIZE bytes into an NAME_SIZE length array? So i think this
> > can be >, not >= ?
> 
> Sorry, I misspoke.
> name_len excludes the trailing \0.

The man page say:

       Upon successful return, these functions return the number of characters
       printed (excluding the null byte used to end output to strings).

       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.
       (See also below under NOTES.)

Assuming the kernel snprintf() follows this, your condition is
correct. So once the commit message is corrected, please add:

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew