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

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Date:	Wed, 30 Apr 2008 11:48:06 +0530
From:	"NAGABHUSHAN BS" <bsn.0007@...il.com>
To:	"Jan Blunck" <jblunck@...e.de>
Cc:	libc-alpha@...rceware.org, "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>,
	"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 9:34 PM, Jan Blunck <jblunck@...e.de> wrote:
> On Tue, Apr 29, bsn.0007@...il.com wrote:
>
>  > The RFC discussed about the information glibc readdir needs to get about
>  > union mounted directories and I have assumed the following information
>  > to be available from the kernel for this implementation.
>  >
>  > - Kernel would return all the dirents (including duplicates and whiteouts)
>  > starting from the topmost directory of the union.
>  >
>  > - Indication that this directory is a union mounted directory
>  >       I have assumed that kernel would return a "." whiteout as the first
>  > directory entry of the union. This would tell glibc readdir(3) that it is
>  > working with a union mounted directory and it needs to do duplicate
>  > elimination and whiteout suppression. It starts building a dirent cache
>  > for this purpose.
>
>  IIRC the intention was to emit a "." whiteout when "changing" from one
>  directory to the next. That means when the first directory is completely read
>  the whiteout is emitted. After that glibc knows to start duplicate
>  removal.
>

Yes the intention was to get a "." whiteout when changing from one
directory to next and thats essentially what i have assumed, for
starting duplicate elimination.
Along with that i have also assumed to get a "." whiteout as the first
directory entry of the union, so as to indicate to glibc that the
directory is a union mounted directory.

Regards
Nagabhushan
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