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authorJan Kara <jack@suse.cz>2007-10-17 02:29:31 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 11:42:56 -0400
commit8e8934695dfd1d5013555a74a9da706a2e301cb0 (patch)
treeedef65302982cbd3e18cf4ef3c88040939886e3a /Documentation
parentfac8b209b1084bc85748bd54e13d00c1262b220f (diff)
quota: send messages via netlink
Implement sending of quota messages via netlink interface. The advantage is that in userspace we can better decide what to do with the message - for example display a dialogue in your X session or just write the message to the console. As a bonus, we can get rid of problems with console locking deep inside filesystem code once we remove the old printing mechanism. Signed-off-by: Jan Kara <jack@suse.cz> Cc: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/quota.txt59
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1
2Quota subsystem
3===============
4
5Quota subsystem allows system administrator to set limits on used space and
6number of used inodes (inode is a filesystem structure which is associated
7with each file or directory) for users and/or groups. For both used space and
8number of used inodes there are actually two limits. The first one is called
9softlimit and the second one hardlimit. An user can never exceed a hardlimit
10for any resource. User is allowed to exceed softlimit but only for limited
11period of time. This period is called "grace period" or "grace time". When
12grace time is over, user is not able to allocate more space/inodes until he
13frees enough of them to get below softlimit.
14
15Quota limits (and amount of grace time) are set independently for each
16filesystem.
17
18For more details about quota design, see the documentation in quota-tools package
19(http://sourceforge.net/projects/linuxquota).
20
21Quota netlink interface
22=======================
23When user exceeds a softlimit, runs out of grace time or reaches hardlimit,
24quota subsystem traditionally printed a message to the controlling terminal of
25the process which caused the excess. This method has the disadvantage that
26when user is using a graphical desktop he usually cannot see the message.
27Thus quota netlink interface has been designed to pass information about
28the above events to userspace. There they can be captured by an application
29and processed accordingly.
30
31The interface uses generic netlink framework (see
32http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more
33details about this layer). The name of the quota generic netlink interface
34is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>.
35 Currently, the interface supports only one message type QUOTA_NL_C_WARNING.
36This command is used to send a notification about any of the above mentioned
37events. Each message has six attributes. These are (type of the argument is
38in parentheses):
39 QUOTA_NL_A_QTYPE (u32)
40 - type of quota being exceeded (one of USRQUOTA, GRPQUOTA)
41 QUOTA_NL_A_EXCESS_ID (u64)
42 - UID/GID (depends on quota type) of user / group whose limit
43 is being exceeded.
44 QUOTA_NL_A_CAUSED_ID (u64)
45 - UID of a user who caused the event
46 QUOTA_NL_A_WARNING (u32)
47 - what kind of limit is exceeded:
48 QUOTA_NL_IHARDWARN - inode hardlimit
49 QUOTA_NL_ISOFTLONGWARN - inode softlimit is exceeded longer
50 than given grace period
51 QUOTA_NL_ISOFTWARN - inode softlimit
52 QUOTA_NL_BHARDWARN - space (block) hardlimit
53 QUOTA_NL_BSOFTLONGWARN - space (block) softlimit is exceeded
54 longer than given grace period.
55 QUOTA_NL_BSOFTWARN - space (block) softlimit
56 QUOTA_NL_A_DEV_MAJOR (u32)
57 - major number of a device with the affected filesystem
58 QUOTA_NL_A_DEV_MINOR (u32)
59 - minor number of a device with the affected filesystem