On Mon, 09 Jul 2012 17:30:48 -0700 ebied...@xmission.com (Eric W. Biederman)
wrote:
> Andrew Morton <a...@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.
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