From: Dmitry Monakhov <dmonakhov@openvz.org>
Subject: Re: [PATCH 3/5] ext4: Implement project ID support for ext4 filesystem
Date: Fri, 19 Mar 2010 11:16:14 +0300
Message-ID: <87fx3wg20h.fsf@openvz.org>
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Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	tytso@mit.edu, hch@infradead.org, jack@suse.cz,
	david@fromorbit.com, viro@ZenIV.linux.org.uk, xemul@openvz.org
To: Andreas Dilger <adilger@sun.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
In-Reply-To: <41219796-D9F2-4292-9284-E8D266EB3532@sun.com> (Andreas Dilger's
	message of "Thu, 18 Mar 2010 15:25:00 -0600")
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Andreas Dilger <adilger@sun.com> writes:

> On 2010-03-18, at 08:02, Dmitry Monakhov wrote:
>> * Disk layout
>>  Project id is stored on disk inside xattr usually inside ibody.
>>  Xattr is used only as a data storage, It has not user visible xattr
>>  interface.
>>
>> * User interface
>>  Project id is accessible via generic xattr interface
>> "system.project_id"
>>
>> +#define EXT4_XATTR_INDEX_PROJECT_ID	        7
>
> If you are making this attribute available to userspace via
> system.project_id, doesn't it make sense to store it on disk as
> system.project_id also (i.e. in the "system" namespace)?
>
> Alternately, the "trusted" namespace is already intended for use as
> "accessible only by root/kernel" semantics if this is what you are
> trying to achieve.
Yess, may be it will be better storage class for projectid.
> I'm also with the statement "It has not user visible xattr interface"
> yet you also write "Project id is accessible via generic xattr
> interface".  Why bother having this complexity when you are free to
> make the two identical?
Ohh. obviously sentence that 'xattr is not visible' is obsolete.
I'v forgot to change it after prjid becomes visible xattr, sorry
for ambiguity.
>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.