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From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCH] proc: restore seekdir("/proc", 256) semantics
Date: Thu, 3 May 2018 20:13:23 +0300	[thread overview]
Message-ID: <20180503171323.GA2137@avx2> (raw)
In-Reply-To: <20180501152307.61113cd16c2c1bec38ac1155@linux-foundation.org>

On Tue, May 01, 2018 at 03:23:07PM -0700, Andrew Morton wrote:
> On Tue, 24 Apr 2018 00:50:09 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > Long time ago "/proc/self" was an honest symlink and all not-PID entries
> > were output before /proc/$PID. To not lose /proc/self in readdir output
> > after it became permanently positive dentry it was stuck before /proc/1.
> > 
> > One side effect of the change was that the code
> > 
> > 	d = opendir("/proc");
> > 	seekdir(d, 256);
> > 
> > stopped pointing to the first PID for applications that want to skip all
> > the crap.
> > 
> > Later "/proc/thread-self" was added in the same way.
> > 
> > It looks like ps and top aren't seeking over /proc but are simply
> > skipping over so nobody noticed.
> > 
> > Restore old behaviour, make seekdir(254) point to /proc/self and
> > seekdir(255) point to /proc/thread-self.
> > 
> 
> Gee.  Why?  That's a pretty weird artifact in the userspace API and if
> we were able to withdraw it without damage then good, let's leave it
> withdrawn?

I checked ps, top and htop, they are not doing seekdir(256).
Apparently userspace devs were unaware of this trick.
I'll remove this before anyone notices.

> I mean, if we're to make this a permanent part of the userspace API
> then it should be documented in the proc(5) manpage and we should have
> something in tools/testing/selftests to detect regressions in the
> interface.  Good luck with all that!

  reply	other threads:[~2018-05-03 17:13 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-23 21:50 Alexey Dobriyan
2018-05-01 22:23 ` Andrew Morton
2018-05-03 17:13   ` Alexey Dobriyan [this message]
2018-05-02 19:10 ` Pavel Machek

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