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

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Message-ID: <20120825231952.GX23464@ZenIV.linux.org.uk>
Date:	Sun, 26 Aug 2012 00:19:52 +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 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?

Another thing:
			f_flags = fd_file->f_flags & ~O_CLOEXEC;
in there is really wrong; we shouldn't leak that bit into ->f_flags
at all (which is properly fixed in fs/open.c).  Close-on-exec is
a property of descriptor, not of file...

tid_fd_revalidate(): these dances with get_files_struct()/put_files_struct()
are pointless.  We really only need "is it opened" + f_mode if it is.
Extracting that information is cheap enough to have it done right under
task_lock() (see what get_files_struct() is doing); no need to mess with
files_struct refcount, etc.

proc_fd_link() and seq_fd_open(): ditto.

As the matter of fact, the only place in there where get_files_struct() is
warranted is proc_readfd_common().

intantiate callback: sodding atrocity; as the absolute minimum it should
lose its "dir" argument.  dentry->d_parent->d_inode is stable (we are
holding ->i_mutex on parent in all callers) and it's equal to dir in all
cases.
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