linux-kernel - Re: [PATCH 1/4] mtd: Add sysfs attr to expose ECC stats

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Message-ID: <20140513111524.GA29552@kroah.com>
Date:	Tue, 13 May 2014 13:15:24 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	"Gupta, Pekon" <pekon@...com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] mtd: Add sysfs attr to expose ECC stats

On Mon, May 12, 2014 at 11:26:14PM -0300, Ezequiel Garcia wrote:
> On 12 May 05:50 PM, Brian Norris wrote:
> > > There are some guidelines about attributes in 'Documentation/filesystems/sysfs.txt'
> > > Though it's acceptable to put array of values of the "same type" in single sysfs file,
> > > But I'm still not confident on having all members of 'struct ecc_stats' being
> > > represented by single sysfs file
> > [...]
> > 
> > I agree, it looks like the sysfs policy would recommend against putting
> > distinct properties in the same file.
> > 
> 
> OK...
> 
> > I'm not sure if /sys/block/<disk>/stat is a good example, as it does
> > violate this policy. It also seems to have some historical baggage.
> > 
> > But there is potentially one good reason for putting this distinct
> > information in a single file: if the information must be returned
> > atomically. For disk stats, it might be important to get a consistent
> > snapshot of the disk stats (or nearly so, with minimal locking
> > overhead), which might change significantly between file accesses if
> > we're doing half a dozen file queries instead.
> > 
> > This same reason may not apply to these ECC stats, since none of these
> > ECC stats are likely to be changing concurrently.
> > 
> 
> Right.
> 
> > So I personally might lean toward "one file per attribute" here.
> > 
> 
> Yup, no problem. Greg, if you can confirm this it'd be great.

Yes, that is the rule for sysfs, please do not put multiple values in a
single sysfs file for a variety of good reasons.

> > > >> I hope this will still keep it machine readable.
> > > >Well, this is not a debugfs entry, so I'm not sure we want to add such debug
> > > >information. Anyone can take a look at the code and see what ecc_stats mean.
> > 
> > The code or (as suggested by Pekon) the documentation
> > (Documentation/ABI/). Either way -- with a single 'ecc_stats' table, or
> > with 4 separate files -- they need to be documented.
> > 
> 
> Sure, will document in next round.

This documentation is required, thanks.

greg k-h
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