linux-kernel - Re: [PATCH] [RFCv2] notify userspace about time changes

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Date:	Fri, 20 Aug 2010 11:37:23 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Greg KH <gregkh@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexander Shishkin <virtuoso@...nd.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Jon Hunter <jon-hunter@...com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Avi Kivity <avi@...hat.com>, John Kacur <jkacur@...hat.com>,
	Chris Friesen <chris.friesen@...band.com>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFCv2] notify userspace about time changes

On Thu, Aug 19, 2010 at 08:31:27AM -0700, Greg KH wrote:
> On Thu, Aug 19, 2010 at 11:36:12AM +0300, Kirill A. Shutemov wrote:
> > On Wed, Aug 18, 2010 at 09:09:37PM -0700, Greg KH wrote:
> > > On Wed, Aug 18, 2010 at 04:53:03PM -0700, Andrew Morton wrote:
> > > > Is sysfs the right interface for this thing?  Bear in mind that
> > > > CONFIG_SYSFS does exist.  
> > > > 
> > > > > +		     fd = open("/sys/kernel/time_notify", O_WRONLY);
> > > > > +		     fdprintf(fd, "%d 1 0 1 1", efd);
> > > > 
> > > > why not
> > > > 
> > > > 		sys_time_notify(efd, 1, 0, 1, 1);
> > > 
> > > Yeah, that would be much better than a sysfs file, this is abusing the
> > > sysfs interface quite a lot.
> > 
> > Do you really think, that increasing number of syscalls is better then
> > fs-based interfaces?
> 
> As you are pretty much creating a new syscall here anyway, there is no
> problem with making it a real one, right?

I think Linux has too many syscalls. Significant part these interfaces
would be better to map to a filesystem[s].

> That way you can properly
> handle the user/kernel documentation and persistance over time (i.e. you
> can't change it.)

On the other, hand properly designed fs-based interface requires less
modification of userspeace to use it. Acctually, you can use most of
fs-based intefaces directly from shell. No need in libc modifications and
utilities to use it from shell or other script language.
See cgroup, for example.

> So yes, a syscall would be better, especially as this does not exactly
> fit into the model of sysfs, right?

Yes, sysfs is not the best place for it, but...

-- 
 Kirill A. Shutemov
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