linux-kernel - Re: compat_sys_times() bogus until jiffies >= 0.

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Message-ID: <jetznxt4wu.fsf@sykes.suse.de>
Date:	Thu, 08 Nov 2007 11:20:17 +0100
From:	Andreas Schwab <schwab@...e.de>
To:	David Miller <davem@...emloft.net>
Cc:	paulus@...ba.org, akpm@...ux-foundation.org, lkml@...idb.org,
	linux-kernel@...r.kernel.org, drepper@...hat.com,
	mtk-manpages@....net
Subject: Re: compat_sys_times() bogus until jiffies >= 0.

David Miller <davem@...emloft.net> writes:

> I agree with this analysis.
>
> The Linux man page for times() explicitly lists (clock_t) -1 as a
> return value meaning error.
>
> So even if we did make some effort to return errors "properly" (via
> force_successful_syscall_return() et al.) userspace would still be
> screwed because (clock_t) -1 would be interpreted as an error.
>
> Actually I think this basically proves we cannot return (clock_t) -1
> ever because all existing userland (I'm not talking about inside
> glibc, I'm talking about inside of applications) will see this as an
> error.
>
> User applications have no other way to check for error.
>
> This API is definitely very poorly designed, no matter which way we
> "fix" this some case will remain broken.

A possible remedy is to return the ticks since process start time, which
delays the wrap around much further.  POSIX only demands consistency
within the same process.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@...e.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."
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