mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-12-29 01:05:29 +00:00
476fdf14e5
Switch link to Sourceforge in quota documentation to https and replace link for libnl documentation with a working one from infradead. Signed-off-by: Jan Kara <jack@suse.cz>
86 lines
3.3 KiB
ReStructuredText
86 lines
3.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===============
|
|
Quota subsystem
|
|
===============
|
|
|
|
Quota subsystem allows system administrator to set limits on used space and
|
|
number of used inodes (inode is a filesystem structure which is associated with
|
|
each file or directory) for users and/or groups. For both used space and number
|
|
of used inodes there are actually two limits. The first one is called softlimit
|
|
and the second one hardlimit. A user can never exceed a hardlimit for any
|
|
resource (unless he has CAP_SYS_RESOURCE capability). User is allowed to exceed
|
|
softlimit but only for limited period of time. This period is called "grace
|
|
period" or "grace time". When grace time is over, user is not able to allocate
|
|
more space/inodes until he frees enough of them to get below softlimit.
|
|
|
|
Quota limits (and amount of grace time) are set independently for each
|
|
filesystem.
|
|
|
|
For more details about quota design, see the documentation in quota-tools package
|
|
(https://sourceforge.net/projects/linuxquota).
|
|
|
|
Quota netlink interface
|
|
=======================
|
|
When user exceeds a softlimit, runs out of grace time or reaches hardlimit,
|
|
quota subsystem traditionally printed a message to the controlling terminal of
|
|
the process which caused the excess. This method has the disadvantage that
|
|
when user is using a graphical desktop he usually cannot see the message.
|
|
Thus quota netlink interface has been designed to pass information about
|
|
the above events to userspace. There they can be captured by an application
|
|
and processed accordingly.
|
|
|
|
The interface uses generic netlink framework (see
|
|
https://lwn.net/Articles/208755/ and http://www.infradead.org/~tgr/libnl/ for
|
|
more details about this layer). The name of the quota generic netlink interface
|
|
is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>. Since
|
|
the quota netlink protocol is not namespace aware, quota netlink messages are
|
|
sent only in initial network namespace.
|
|
|
|
Currently, the interface supports only one message type QUOTA_NL_C_WARNING.
|
|
This command is used to send a notification about any of the above mentioned
|
|
events. Each message has six attributes. These are (type of the argument is
|
|
in parentheses):
|
|
|
|
QUOTA_NL_A_QTYPE (u32)
|
|
- type of quota being exceeded (one of USRQUOTA, GRPQUOTA)
|
|
QUOTA_NL_A_EXCESS_ID (u64)
|
|
- UID/GID (depends on quota type) of user / group whose limit
|
|
is being exceeded.
|
|
QUOTA_NL_A_CAUSED_ID (u64)
|
|
- UID of a user who caused the event
|
|
QUOTA_NL_A_WARNING (u32)
|
|
- what kind of limit is exceeded:
|
|
|
|
QUOTA_NL_IHARDWARN
|
|
inode hardlimit
|
|
QUOTA_NL_ISOFTLONGWARN
|
|
inode softlimit is exceeded longer
|
|
than given grace period
|
|
QUOTA_NL_ISOFTWARN
|
|
inode softlimit
|
|
QUOTA_NL_BHARDWARN
|
|
space (block) hardlimit
|
|
QUOTA_NL_BSOFTLONGWARN
|
|
space (block) softlimit is exceeded
|
|
longer than given grace period.
|
|
QUOTA_NL_BSOFTWARN
|
|
space (block) softlimit
|
|
|
|
- four warnings are also defined for the event when user stops
|
|
exceeding some limit:
|
|
|
|
QUOTA_NL_IHARDBELOW
|
|
inode hardlimit
|
|
QUOTA_NL_ISOFTBELOW
|
|
inode softlimit
|
|
QUOTA_NL_BHARDBELOW
|
|
space (block) hardlimit
|
|
QUOTA_NL_BSOFTBELOW
|
|
space (block) softlimit
|
|
|
|
QUOTA_NL_A_DEV_MAJOR (u32)
|
|
- major number of a device with the affected filesystem
|
|
QUOTA_NL_A_DEV_MINOR (u32)
|
|
- minor number of a device with the affected filesystem
|