linux-kernel - Re: [PATCH 1/2] namespaces: give each namespace a serial number

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Message-ID: <20140501225116.GB25669@mail.hallyn.com>
Date:	Fri, 2 May 2014 00:51:16 +0200
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Richard Guy Briggs <rgb@...hat.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, serge.hallyn@...ntu.com,
	eparis@...hat.com, sgrubb@...hat.com, ebiederm@...ssion.com
Subject: Re: [PATCH 1/2] namespaces: give each namespace a serial number

Quoting Richard Guy Briggs (rgb@...hat.com):

Most of this looks reasonable, but I'm curious about something,

> +/**
> + * ns_serial - compute a serial number for the namespace
> + *
> + * Compute a serial number for the namespace to uniquely identify it in
> + * audit records.
> + */
> +unsigned int ns_serial(void)
> +{
> +	static DEFINE_SPINLOCK(serial_lock);
> +	static unsigned int serial = 4; /* reserved for IPC, UTS, user, PID */
> +
> +	unsigned long flags;
> +	unsigned int ret;
> +
> +	spin_lock_irqsave(&serial_lock, flags);
> +	do {
> +		ret = ++serial;
> +	} while (unlikely(!ret));

Why exactly are you doing this?  Surely if serial is going to
wrap around we've got a bigger problem than just wanting go
bump one more time?

> +	spin_unlock_irqrestore(&serial_lock, flags);
> +
> +	return ret;
> +}
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