linux-kernel - Re: [PATCH] FILESYSTEMS: Delete unused "int dummy[5]" from inodes_stat

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Date:	Tue, 29 May 2007 13:44:42 -0500
From:	"Josh Boyer" <jwboyer@...il.com>
To:	"Randy Dunlap" <randy.dunlap@...cle.com>
Cc:	"Robert P. J. Day" <rpjday@...dspring.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Alexander Viro" <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] FILESYSTEMS: Delete unused "int dummy[5]" from inodes_stat_t.

On 5/29/07, Randy Dunlap <randy.dunlap@...cle.com> wrote:
> Robert P. J. Day wrote:
> > On Tue, 29 May 2007, Randy Dunlap wrote:
> >
> >> On Tue, 29 May 2007 14:07:01 -0400 (EDT) Robert P. J. Day wrote:
> >>
> >>> On Tue, 29 May 2007, Andrew Morton wrote:
> >>>
> >>>> kernel/sysctl.c:
> >>>>
> >>>>    {
> >>>>            .ctl_name       = FS_STATINODE,
> >>>>            .procname       = "inode-state",
> >>>>            .data           = &inodes_stat,
> >>>>            .maxlen         = 7*sizeof(int),    <-----
> >>>>            .mode           = 0444,
> >>>>            .proc_handler   = &proc_dointvec,
> >>>>    },
> >>>>
> >>>> akpm:/home/akpm> cat /proc/sys/fs/inode-state
> >>>> 608039  178454  0       0       0       0       0
> >>>>
> >>>> So it _is_ used: to present those five zeroes.  I think this is
> >>>> for back-compatibility with some cretaceous-era kernel.
> >>> ah, gotcha.  well, i'll leave this up to someone else to do
> >>> anything with if they are so inclined.
> >> There's little to be done, except possibly put a /* comment */ on
> >> the struct's dummy line so that we don't go thru this again in N
> >> years.
> >
> >   so, just to clarify, what *is* the value of those trailing five
> > zeroes?  andrew suggests it's to be backward-compatible with an old
> > kernel, which doesn't make much sense to me.  it would make more sense
> > to say that that's backward-compatible with some old userspace app
> > that always wants to see seven values and just ignores the last five.
>
> Agreed, it's for compat with some (unknown) userspace app that reads
> /proc/sys/fs/inode-state and scans for 7 (or more than 2) numbers there.
> The mantra is "don't break userspace," so we leave the numbers there...

Couldn't you remove the dummy member and just have the proc entry
print out 5 dummy zeros?

josh
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