linux-kernel - Re: [RFC PATCH 0/2] Union Mount: Directory listing in glibc

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Date:	Wed, 30 Apr 2008 11:37:10 +0530
From:	"NAGABHUSHAN BS" <bsn.0007@...il.com>
To:	"Erez Zadok" <ezk@...sunysb.edu>
Cc:	libc-alpha@...rceware.org, "Jan Blunck" <jblunck@...e.de>,
	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>,
	"Trond Myklebust" <trond.myklebust@....uio.no>,
	bharata@...ux.vnet.ibm.com, "David Woodhouse" <dwmw2@...radead.org>
Subject: Re: [RFC PATCH 0/2] Union Mount: Directory listing in glibc

On Tue, Apr 29, 2008 at 9:19 PM, Erez Zadok <ezk@...sunysb.edu> wrote:
> In message <20080429133201.GA9938@...alhost.localdomain>, bsn.0007@...il.com writes:
>  > Hi,
>  >
>  > I went through Bharata's RFC post on glibc based Union Mount readdir solution
>  > (http://lkml.org/lkml/2008/3/11/34) and have come up with patches
>  > against glibc to implement the same.
>  [...]
>
>  The last set of discussions on glibc support ended, as I understood it, with
>  the glibc people objecting to such "special-purpose" code in glibc.  See
>  <http://lkml.org/lkml/2008/3/11/66>.  So has anything changed behind the
>  scenes, or is this idea unlikely to be merged into glibc any time soon, if
>  ever.  (Personally I'd love to rip out the readdir-related code from unionfs
>  if glibc supported the same.)
>
>
>  > Patch 1. readdir support for union mounted directories.
>  >       I am caching the dirent names in a list to aid duplicate elimination.
>  > And this cache is stored in DIRP. For duplicate elimination I am using
>  > strcmp(). I am not sure if this works universally with different types
>  > of filesystems. Any suggestions here would be welcome.
>  [...]
>
>  You might consider using a hash table instead of a list; it'll be faster in
>  case where there are a lot of whiteouts/duplicates to process.
>

Yes, hash table was one of the things i had considered  to use as a
cache. But i am not completely sure how this would support seekdir.
Any suggestions are greatly welcome.

Regards Nagabhushan
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