linux-kernel - Re: [patch 1/9] procfs: Move /proc/pid/fd[info] handling code to fd.[ch]

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Date:	Sat, 25 Aug 2012 18:55:04 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>,
	aneesh.kumar@...ux.vnet.ibm.com, bfields@...ldses.org
Subject: Re: [patch 1/9] procfs: Move /proc/pid/fd[info] handling code to
 fd.[ch]

On Sat, Aug 25, 2012 at 09:39:58PM +0400, Cyrill Gorcunov wrote:
> On Sat, Aug 25, 2012 at 06:16:05PM +0100, Al Viro wrote:
> > On Thu, Aug 23, 2012 at 02:43:24PM +0400, Cyrill Gorcunov wrote:
> > > This patch prepares the ground for further extension of
> > > /proc/pid/fd[info] handling code by moving fdinfo handling
> > > code into fs/proc/fd.c.
> > > 
> > > I think such move makes both fs/proc/base.c and fs/proc/fd.c
> > > easier to read.
> > 
> > BTW, looking at the other stuff in fs/proc/base.c, why the hell is
> > struct file * grabbed in proc_map_files_readdir()?  All we do with
> > it is passing it to proc_fill_cache(), which passes it to
> > proc_map_files_instantiate(), which looks at two sodding bits
> > in file->f_mode.  Then we go and fput() all those struct file
> > references we'd been putting into the array...  What for?
> 
> Well, this could be simplified indeed, if I understand you correctly
> you propose just save f_mode in flexible array and use it instead
> of struct file, right? (which will require to rewrite code a bit)

Yes.  FWIW, proc_fill_cache() is really atrocious ;-/  Not to mention
anything else, if we ever get a negative dentry there, we have a dentry
leak.  I don't think it's possible in practice, but...  Furthermore,
        if (!child || IS_ERR(child) || !child->d_inode)
                goto end_instantiate;
        inode = child->d_inode;
        if (inode) {
                ino = inode->i_ino;
                type = inode->i_mode >> 12;
        }
        dput(child);
looks really weird - how can we possibly get !inode when we'd just
checked that child->inode is non-NULL?  Moreover, that find_inode_number()
a bit below is also as weird as it gets - in effect, we repeat
d_lookup() we'd just done earlier.  How *can* it get us anything?
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