linux-ext4 - Re: DRAFT Design Spec for 1st Class Quota Support in Ext4

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Date:	Mon, 26 Apr 2010 12:11:28 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: DRAFT Design Spec for 1st Class Quota Support in Ext4

"Theodore Ts'o" <tytso@....edu> writes:

> Please comment!
>
> 		    1st Class Quota Support in Ext4
> 		    DRAFT Design Specification, v0.5
>
>
> This proposal promotes quota to being a first class supported feature in
> ext4.  To do this, we will do the following:
>
> 1)  We define the following two new fields to the superblock.  No new
> COMPAT features are defined; since unused superblock fields are zero, if
> the fields are not known.
>   *) A superblock field containing the inode number for the user quota
>      file.  This inode number will be 3 if the inode is user quota file
>      is hidden.  If this field is zero, then user quotas will not be tracked.
>   *) A superblock field containing the inode number for the group quota
>      file.  This inode number will be 4 if the inode is group quota file
>      is hidden.  If this field is zero, then group quotas will not be
>      tracked.
>
I now that it is always not right time for ask about this, but still.
Don't you mind to reserve 5'th inode number for projectID quota?
> 2) The quota files will use the v2 format only, and updates to the quota
> files will be protected with the journal if the journal is present.
Since we are about to starting huge movements let's use new (v3) quota
format. The only difference with v2 is extended header wider than old
magic+version.

struct v3_disk_dqheader {
        __le32 dqh_magic;        /* Magic number identifying file */
        __le32 dqh_version;      /* File version */
        __le32 dqh_state;        /* quota file  state */
        __u32  dqh_reserved[125];
 };
dqh_state is an equivalent of sb's s_state.
>
> 3) If e2fsck needs to do a full file system consistency check, it will
> keep track of the disk space used by each user and/or groups ids, and
> update the user and/or group quota files at the end of the e2fsck run.
>
> 4) If the filesystem appears consistent, but the user and/or group quota
> fils are not equal to the last superblock write time, e2fsck will do a
> partical file system consistency check.  This will consist of e2fsck
> pass #1, and if no errors were detected, e2fsck will update the user and
> group quota files and exit.  If any errors were detected during pass #1,
> then e2fsck will  continue to do pass numbers 2-5, and thus do a full
> file system consistency check before updating the quota files.
>
> 5) Mke2fs will take an extended option (quota=user,group) which if
> present will force the initialization of the quota inodes.  Using the
> /etc/mke2fs.conf file, the system administrator can also specify a quota
> option in the [defaults] and [fs_types] section, so that quota files can
> be enabled by default.
>
> 6) Tune2fs will have a facility for adding and removing user and group
> quotas inodes while the file system is mounted.  The quota usage will
> not be correct after the quota inodes are newly added, however, so quota
> will not be enabled by default,  If the quota inodes are removed, quota
> will be disabled first.
  Who is responsible for quota enabling in that scenario?
  Will it enabled by default on mount time?

Small note: quotacheck -cug /mnt will result in unlink/create
so we have options exclusive options:
if inode is already exist
  replace unlink/create with truncate
else
  call tune2fs from quotacheck after inodes was created.
>
> 7) There will be a new interface so that bulk quota information can be
> fetched from the file system.  This needs to be negotiated with Jan
> Kara.  It can either be a new system call, or a magic file in /proc that
> can be opened and the repquota data extracted.
>
> 8) Traditional style quota will still be supported; that is the
> appropriate magic flags will be passed through to /proc/mounts so that
> the old-style init scripts will still function correctly.  This support
> will be deprecated over an 18 month period after the new-style kernel
> code and userspace tools have been released.
  9) Make ext4_orphan_cleanup() more tolerate to quota, if quota is 
  enabled for given SB, but cleanup procedure is unable to perform
  ext4_quota_on_mount() mount should fail as it does in case of wrong
  options.

The rest is looking very promising.
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