On Mon 29-08-11 15:42:36, Aditya Kali wrote: > 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. OK, probably makes sense in the long run. I'll update quota tools to use GETFMT quotactl then... > >> 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)? Yes. > >> 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 Ah, I see. OK. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
