From: Andrew Morton <akpm@linux-foundation.org>
To: ebiederm@xmission.com (Eric W. Biederman)
Cc: Glauber Costa <glommer@parallels.com>,
<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
Greg Thelen <gthelen@google.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
Tejun Heo <tj@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v2] fail dentry revalidation after namespace change
Date: Mon, 9 Jul 2012 17:47:05 -0700 [thread overview]
Message-ID: <20120709174705.0e2078c8.akpm@linux-foundation.org> (raw)
In-Reply-To: <87txxgxxs7.fsf@xmission.com>
On Mon, 09 Jul 2012 17:30:48 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote:
> Andrew Morton <akpm@linux-foundation.org> writes:
>
> >> {
> >> struct sysfs_dirent *sd;
> >> int is_dir;
> >> + int type;
> >>
> >> if (nd->flags & LOOKUP_RCU)
> >> return -ECHILD;
> >> @@ -326,6 +327,13 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
> >> if (strcmp(dentry->d_name.name, sd->s_name) != 0)
> >> goto out_bad;
> >>
> >> + /* The sysfs dirent has been moved to a different namespace */
> >> + type = KOBJ_NS_TYPE_NONE;
> >> + if (sd->s_parent)
> >> + type = sysfs_ns_type(sd->s_parent);
> >> + if (type && (sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns))
> >
> > eww, the code is assuming that KOBJ_NS_TYPE_NONE has a value of zero.
> > Don't do that; it smells bad.
>
> Gag. An incomplete change in idiom.
>
> KOBJ_NS_TYPE_NONE is explicitly defined as 0 so that it can be used
> this way, and every where else in fs/sysfs/dir.c uses this idiom.
One man's idiom is another man's idiocy.
Seriously. What sort of idea is that? Create an enumerated type and
then just ignore it?
> Pray tell in what parallel universe is that monstrosity above more
> readable than the line it replaces?
Don't be silly, it is not a "monstrosity". The code it is modifying
contains an unneeded test-and-branch. It's a test and branch which the
compiler might be able to avoid. If we can demonstrate that the
compiler does indeed optimise it, or if we can find a less monstrous
way of implementing it then fine. Otherwise, efficiency wins.
next prev parent reply other threads:[~2012-07-10 0:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-06 9:09 [PATCH v2] fail dentry revalidation after namespace change Glauber Costa
2012-07-06 9:37 ` Eric W. Biederman
2012-07-06 9:44 ` Glauber Costa
2012-07-06 9:51 ` Eric W. Biederman
2012-07-09 23:13 ` Andrew Morton
2012-07-09 23:43 ` Serge Hallyn
2012-07-10 0:30 ` Eric W. Biederman
2012-07-10 0:47 ` Andrew Morton [this message]
2012-07-10 1:51 ` Eric W. Biederman
2012-07-10 2:15 ` Andrew Morton
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