Thanks for your feedback. On Mon, Aug 29, 2011 at 2:57 PM, Jan Kara <jack@xxxxxxx> wrote: > On Fri 19-08-11 12:06:09, Aditya Kali wrote: >> This patch is an attempt towards supporting quotas as first class >> feature in ext4. It is based on the proposal at: >> https://ext4.wiki.kernel.org/index.php/Design_For_1st_Class_Quota_in_Ext4 >> This patch introduces a new feature - EXT4_FEATURE_RO_COMPAT_QUOTA which, when >> turned on, enables quota accounting at mount time iteself. Also, the >> quota inodes are stored in two additional superblock fields. >> Some changes introduced by this patch that should be pointed out are: >> 1) Two new ext4-superblock fields - s_usr_quota_inum and s_grp_quota_inum >> for storing the quota inodes in use. >> 2) If the QUOTA feature and corresponding quota inodes are set in superblock, >> Quotas are turned on at mount time irrespective of the quota mount options. >> Thus the mount options 'quota', 'usrquota' and 'grpquota' are completely >> ignored with the new QUOTA feature flag. > Hmm, cannot we automatically enable 'usrquota' and 'grpquota' options > when we see QUOTA feature enabled? Quota tools still need these options to > identify a filesystem they can work with (although another option would be > to change quota tools to use GETFMT with ext4 filesystem to identify > whether quotas are enabled or not). > In my current change, these options are just ignored, and the user can still set them if any user tools depend on them while mounting/remounting the filesystem. The design wiki (https://ext4.wiki.kernel.org/index.php/Design_For_1st_Class_Quota_in_Ext4#How_can_userspace_tell_if_quota_is_enabled.3F) mentions that 'usrquota' & 'grpquota' options won't be used (so I was under impression that they are being deprecated). Also, if these are set automatically on mount, it would mean that the user wont be able to set these options anymore. >> 3) Default quota inodes are: inode#3 for tracking userquota and inode#4 for >> tracking group quota. The superblock fields can be set to use other inodes >> as well. >> 4) mke2fs or tune2fs will initialize these inodes when quota feature is >> being set. The default reserved inodes will not be visible to user as >> regular files. >> 5) Once quotas are turned on, they cannot be turned off while the FS is >> mounted. This is because we do not want to let the quota get inconsistent. > Both xfs and ocfs2 allow for mode in which usage is tracked (i.e. quota > information is kept uptodate) but limits are not enforced. I imagine this > might be useful in some cases and also from consistency point of view it > would be nice. > > In ocfs2 I implemented it so that on mount, updating of quota information > is enabled (when appropriate fs feature is enabled) but limits are not > enforced. Quotaon/quotaoff commands then toggle enforcement of quota > limits. XFS has mount options which decide whether quota information should > be kept uptodate and whether it should be enforced or not. Enabling only usage on mount makes sense. The limits can then be turned on using quotaon. I assume then we will also need to allow turning the limits off by user (instead of completely denying quotaoff)? > >> 6) With the QUOTA feature set, since the quota inodes are hidden, some of the >> utilities from quota-tools will no longer work correctly. Instead, e2fsprogs >> will include support for fixing the quota files. > I think it might be useful in some cases to enable only user quotas but > leave group quotas disabled (it slightly reduces quota overhead - mainly > because we have less quota structures to update on disk). So it would be > useful to have USRQUOTA and GRPQUOTA features separate... > It is possible to enable only one type of quotas. Instead of having two filesystem features, there are already two superblock fields s_usr_quota_inum and s_grp_quota_inum. The enabling can be disabled by setting the corresponding field to '0'. This is also supported via tune2fs: # to enable only user quotas and not group quotas: $ tune2fs -Q usrquota /dev/ram1 # this will set the 'quota' feature in superblock and initialize only usrquota inode. # to enable both user and group quotas: $ tune2fs -Q usrquota,grpquota /dev/ram1 > Honza -- Aditya -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
