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SubjectRe: [patch 3/8] procfs: Add ability to plug in auxiliary fdinfo providers
On Wed, Aug 15, 2012 at 10:16:28PM +0100, Al Viro wrote:
> On Wed, Aug 15, 2012 at 01:21:19PM +0400, Cyrill Gorcunov wrote:
> > -static int fdinfo_open_helper(struct inode *inode, int *f_flags, struct path *path)
> > +static int fdinfo_open_helper(struct inode *inode, int *f_flags, struct file **f_file, struct path *path)
>
> Bloody bad taste, that... This kind of optional arguments is almost always
> a bad sign - tends to happen when you have two barely related functions
> crammed into one. And yes, proc_fd_info() suffers the same braindamage.
> Trying to avoid code duplication is generally a good thing, but it's not
> always worth doing - less obfuscated code wins.

Sure I'll update. Thanks.

> > static int seq_show(struct seq_file *m, void *v)
> > {
> > struct proc_fdinfo *fdinfo = m->private;
> > - seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
> > - (long long)fdinfo->f_pos,
> > - fdinfo->f_flags);
> > - return 0;
> > + int ret;
> > +
> > + ret = seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
> > + (long long)fdinfo->f_file->f_pos,
> > + fdinfo->f_flags);
>
> Realistically, that one is not going to overflow; you are almost certainly
> wasting more cycles on that check of !ret just below than you'll save on
> not going into ->show_fdinfo() in case of full buffer.

Yes, this is redundant, thanks. Will fix.

>
> > + if (!ret && fdinfo->f_file->f_op->show_fdinfo)
> > + ret = fdinfo->f_file->f_op->show_fdinfo(m, fdinfo->f_file);
> > +
> > + return ret;
> > }
>
> > + ret = single_open(file, seq_show, fdinfo);
> > + if (ret) {
> > + put_filp(fdinfo->f_file);
>
> Excuse me? We should *never* do put_filp() on anything that has already
> been opened. Think what happens if you race with close(); close() would
> rip the reference from descriptor table and do fput(), leaving you with
> the last reference to that struct file. You really don't want to just
> go and free it. IOW, that one should be fput().
>
> > + put_filp(fdinfo->f_file);
> Ditto.

It seems I indeed missed this scenario, thanks Al, will update!

Cyrill


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