linux-kernel - RE: tools: usbip: detach: avoid calling strlen() at each iteration

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB97DA8@AcuExch.aculab.com>
Date:	Wed, 16 Sep 2015 13:44:08 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Aaro Koskinen' <aaro.koskinen@....fi>,
	Eric Curtin <ericcurtin17@...il.com>
CC:	"valentina.manea.m@...il.com" <valentina.manea.m@...il.com>,
	"shuah.kh@...sung.com" <shuah.kh@...sung.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: tools: usbip: detach: avoid calling strlen() at each iteration

From: Aaro Koskinen
> Sent: 15 September 2015 21:56
...
> > -	for (unsigned int i = 0; i < strlen(port); i++)
> > +	unsigned int port_len = strlen(port);
> > +
> > +	for (unsigned int i = 0; i < port_len; i++)
> 
> port is read only in this function, so maybe just use "const" and the
> compiler should know to do the same without adding a new variable?

While I've seen the compiler make the assumption, I'm not sure
it should assume that data that is 'const' in one function cannot
be modified by a called function.
(Unless the compiler has some way of knowing that the called function
cannot obtain a non-const pointer to the referenced data.)
(This is also independent of whether the const pointer is passed
to the function.) 

	David

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