From: Andreas Schwab <schwab@suse•de>
To: Timur Tabi <timur@freescale•com>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: Confused about usercopy_64.c
Date: Mon, 10 Mar 2008 17:53:31 +0100 [thread overview]
Message-ID: <jeabl6ikqc.fsf@sykes.suse.de> (raw)
In-Reply-To: <47D56419.6000704@freescale.com> (Timur Tabi's message of "Mon\, 10 Mar 2008 11\:38\:49 -0500")
Timur Tabi <timur@freescale•com> writes:
> I'm confused about something in usercopy_64.c:
>
> unsigned long copy_from_user(void *to, const void __user *from, unsigned long n)
> {
> if (likely(access_ok(VERIFY_READ, from, n)))
> n = __copy_from_user(to, from, n);
> else
> memset(to, 0, n);
> return n;
> }
>
> If access_ok() returns false, then that means that we cannot copy the data from
> user-space. So why are we returning 'n'?
To tell the caller that the function failed. The result is the number
of bytes _left_ to be copying, ie. zero means success.
Andreas.
--
Andreas Schwab, SuSE Labs, schwab@suse•de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
prev parent reply other threads:[~2008-03-10 16:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-10 16:38 Confused about usercopy_64.c Timur Tabi
2008-03-10 16:50 ` Olof Johansson
2008-03-10 16:53 ` Andreas Schwab [this message]
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