lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20080311124935.GA9121@in.ibm.com>
Date:	Tue, 11 Mar 2008 18:19:35 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	libc-alpha@...rceware.org, Jan Blunck <jblunck@...e.de>,
	Erez Zadok <ezk@...sunysb.edu>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	Christoph Hellwig <hch@....de>,
	Ulrich Drepper <drepper@...hat.com>,
	Mingming Cao <cmm@...ibm.com>,
	Dave Hansen <haveblue@...ibm.com>
Subject: Re: [RFC] Union mount readdir support in glibc

On Tue, Mar 11, 2008 at 01:09:29AM -0700, Roland McGrath wrote:
> It seems very unlikely you'd come up with a version of this plan that we'd
> find acceptable in glibc.  readdir does buffering, sometimes entry format
> conversion, and it can skip dummy entries.  That's it.  It's not going to
> become a big hairy thing with all kinds of new state.  Sorry.

In the approach we are suggesting, at the minimum, glibc readdir would
have to maintain a unified cache of dirents with the knowlege of
whiteouts (DT_WHT). Would that be too much ?

> 
> This really is the kernel filesystem's problem.  It just doesn't make sense
> to expect userland to implement half of your directory semantics for you.
> What are you going to do when you want to export a union directory to NFS?
> readdir is a filesystem operation.  You're implementing a filesystem.

Not really. In Union Mount, most of the unification support is done at
VFS layer with some support from filesystems (for things like
whiteouts). It is Unionfs which implements a new filesystem to achieve
unification. Unification is not purely a kernel filesystem's problem, it
involves both VFS and FS.

> 
> Exposing DT_WHT entries may be useful as a user feature.  (BSD had unions
> with whiteouts years ago, and their ls et al have options to let you see
> and operate on whiteouts explicitly so users can make sense of strange
> situations with unions.)  But even for that, we'd have to consider the
> compatibility issues.

AFAIK, even BSD implements duplicate elimination and whiteout
suppression in the userland.

Thanks for your comments.

Regards,
Bharata.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ