linux-kernel - Re: [PATCH-v2 2/9] target/pr: Use atomic bitop for se_dev_entry->pr

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Message-ID: <20150522113404.GB28758@lst.de>
Date:	Fri, 22 May 2015 13:34:04 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Christoph Hellwig <hch@....de>,
	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>,
	Sagi Grimberg <sagig@...lanox.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH-v2 2/9] target/pr: Use atomic bitop for
	se_dev_entry->pr_reg reservation check

On Fri, May 22, 2015 at 02:05:57AM -0700, Nicholas A. Bellinger wrote:
> On Fri, 2015-05-22 at 10:26 +0200, Christoph Hellwig wrote:
> > On Fri, May 22, 2015 at 06:11:04AM +0000, Nicholas A. Bellinger wrote:
> > > +	clear_bit(1, &orig->pr_reg);
> > 
> > Can you call it ->flags and give the bit a meaningful name?
> 
> The bit is signaling if se_dev_entry has a PR registration active.
> 
> I don't see how ->flags is a more meaningful name without other bits
> defined.

It's pretty normal style: define a flags variable for any sort of
bitops state that might show up, and then give the actual bits a meaningful
name.  There's almost no users of using a magic numberic value with
atomic bitops.

Besides being the usual and thus easier to read style it's also good
future proofing.

> > It would be good to just sort out the registered and co variables
> > here before the RCU changes, as in:
> > 
> > http://git.infradead.org/users/hch/scsi.git/commitdiff/6372d9f62c83acb30d051387c40deb4dbdcaa376
> 
> Why not just keep this patch squashed into the relevant commit in the
> context of the larger RCU conversion..?

Because the logic in and aroudn core_scsi3_pr_seq_non_holder right
now is rather confusing.  So before doing changes to it it's better
to clean it up first, document that cleanup in a standalon patch
and then apply the logic change on top.
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