linux-ext4 - Re: [PATCH 1/3] [RFC] vfs: add generic reserved space management interface

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Message-id: <873a3kqjyy.fsf@openvz.org>
Date:	Wed, 09 Dec 2009 17:51:17 +0300
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org, aneesh.kumar@...ux.vnet.ibm.com,
	cmm@...ibm.com, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 1/3] [RFC] vfs: add generic reserved space management
 interface

Jan Kara <jack@...e.cz> writes:

> On Wed 09-12-09 05:11:24, Dmitry Monakhov wrote:
>> Add new field "i_rsv_blocks" to generic inode. This value is
>> managed similar to i_blocks, i_bytes fileds (protected by i_lock).
>> This generic interface will be used by generic quota code similar
>> to i_blocks.
>   I guess some people won't like bloating the VFS inode. It personally
> makes my "quota" life easier but not that many filesystems need this
> (currently I'm aware of only ext4) so their complaints are reasonable...
Please read my answer to Christoph.
>From other point of view, we may change inode structure like this:
struct quota_ptr
{
        struct dquot            *dquot[MAXQUOTAS];
};
struct quota_rsv_ptr
{
        struct dquot            *dquot[MAXQUOTAS];
        qsize_t                 reservation;
};
struct inode {
....
#ifdef CONFIG_QUOTA
       union {
             struct quota_ptr i_dquot;
             struct quota_rsv_ptr i_dquot_rsv;
       };
#endif
....
};
Most file systems will use i_dquot, and file systems with reservation
will use quota_rsv_ptr.
Imho this is even better than, macro approach. But this requires
huge patch for each fs, but who cares. 
>   If we would eventually decide to go this way, I'd account reserved
> space in bytes - quota is really accounted in bytes (as some filesystems
> need this).
Yes you right, I wasn't happy about this too,  Will redo.
>
> 								Honza
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