1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 =============== 3 ===============
4 Quota subsystem 4 Quota subsystem
5 =============== 5 ===============
6 6
7 Quota subsystem allows system administrator to 7 Quota subsystem allows system administrator to set limits on used space and
8 number of used inodes (inode is a filesystem s 8 number of used inodes (inode is a filesystem structure which is associated with
9 each file or directory) for users and/or group 9 each file or directory) for users and/or groups. For both used space and number
10 of used inodes there are actually two limits. 10 of used inodes there are actually two limits. The first one is called softlimit
11 and the second one hardlimit. A user can neve 11 and the second one hardlimit. A user can never exceed a hardlimit for any
12 resource (unless he has CAP_SYS_RESOURCE capab 12 resource (unless he has CAP_SYS_RESOURCE capability). User is allowed to exceed
13 softlimit but only for limited period of time. 13 softlimit but only for limited period of time. This period is called "grace
14 period" or "grace time". When grace time is ov 14 period" or "grace time". When grace time is over, user is not able to allocate
15 more space/inodes until he frees enough of the 15 more space/inodes until he frees enough of them to get below softlimit.
16 16
17 Quota limits (and amount of grace time) are se 17 Quota limits (and amount of grace time) are set independently for each
18 filesystem. 18 filesystem.
19 19
20 For more details about quota design, see the d 20 For more details about quota design, see the documentation in quota-tools package
21 (https://sourceforge.net/projects/linuxquota). 21 (https://sourceforge.net/projects/linuxquota).
22 22
23 Quota netlink interface 23 Quota netlink interface
24 ======================= 24 =======================
25 When user exceeds a softlimit, runs out of gra 25 When user exceeds a softlimit, runs out of grace time or reaches hardlimit,
26 quota subsystem traditionally printed a messag 26 quota subsystem traditionally printed a message to the controlling terminal of
27 the process which caused the excess. This meth 27 the process which caused the excess. This method has the disadvantage that
28 when user is using a graphical desktop he usua 28 when user is using a graphical desktop he usually cannot see the message.
29 Thus quota netlink interface has been designed 29 Thus quota netlink interface has been designed to pass information about
30 the above events to userspace. There they can 30 the above events to userspace. There they can be captured by an application
31 and processed accordingly. 31 and processed accordingly.
32 32
33 The interface uses generic netlink framework ( 33 The interface uses generic netlink framework (see
34 https://lwn.net/Articles/208755/ and http://ww 34 https://lwn.net/Articles/208755/ and http://www.infradead.org/~tgr/libnl/ for
35 more details about this layer). The name of th 35 more details about this layer). The name of the quota generic netlink interface
36 is "VFS_DQUOT". Definitions of constants below 36 is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>. Since
37 the quota netlink protocol is not namespace aw 37 the quota netlink protocol is not namespace aware, quota netlink messages are
38 sent only in initial network namespace. 38 sent only in initial network namespace.
39 39
40 Currently, the interface supports only one mes 40 Currently, the interface supports only one message type QUOTA_NL_C_WARNING.
41 This command is used to send a notification ab 41 This command is used to send a notification about any of the above mentioned
42 events. Each message has six attributes. These 42 events. Each message has six attributes. These are (type of the argument is
43 in parentheses): 43 in parentheses):
44 44
45 QUOTA_NL_A_QTYPE (u32) 45 QUOTA_NL_A_QTYPE (u32)
46 - type of quota being exceeded (one 46 - type of quota being exceeded (one of USRQUOTA, GRPQUOTA)
47 QUOTA_NL_A_EXCESS_ID (u64) 47 QUOTA_NL_A_EXCESS_ID (u64)
48 - UID/GID (depends on quota type) of 48 - UID/GID (depends on quota type) of user / group whose limit
49 is being exceeded. 49 is being exceeded.
50 QUOTA_NL_A_CAUSED_ID (u64) 50 QUOTA_NL_A_CAUSED_ID (u64)
51 - UID of a user who caused the event 51 - UID of a user who caused the event
52 QUOTA_NL_A_WARNING (u32) 52 QUOTA_NL_A_WARNING (u32)
53 - what kind of limit is exceeded: 53 - what kind of limit is exceeded:
54 54
55 QUOTA_NL_IHARDWARN 55 QUOTA_NL_IHARDWARN
56 inode hardlimit 56 inode hardlimit
57 QUOTA_NL_ISOFTLONGWARN 57 QUOTA_NL_ISOFTLONGWARN
58 inode softlimit is exceede 58 inode softlimit is exceeded longer
59 than given grace period 59 than given grace period
60 QUOTA_NL_ISOFTWARN 60 QUOTA_NL_ISOFTWARN
61 inode softlimit 61 inode softlimit
62 QUOTA_NL_BHARDWARN 62 QUOTA_NL_BHARDWARN
63 space (block) hardlimit 63 space (block) hardlimit
64 QUOTA_NL_BSOFTLONGWARN 64 QUOTA_NL_BSOFTLONGWARN
65 space (block) softlimit is 65 space (block) softlimit is exceeded
66 longer than given grace pe 66 longer than given grace period.
67 QUOTA_NL_BSOFTWARN 67 QUOTA_NL_BSOFTWARN
68 space (block) softlimit 68 space (block) softlimit
69 69
70 - four warnings are also defined for 70 - four warnings are also defined for the event when user stops
71 exceeding some limit: 71 exceeding some limit:
72 72
73 QUOTA_NL_IHARDBELOW 73 QUOTA_NL_IHARDBELOW
74 inode hardlimit 74 inode hardlimit
75 QUOTA_NL_ISOFTBELOW 75 QUOTA_NL_ISOFTBELOW
76 inode softlimit 76 inode softlimit
77 QUOTA_NL_BHARDBELOW 77 QUOTA_NL_BHARDBELOW
78 space (block) hardlimit 78 space (block) hardlimit
79 QUOTA_NL_BSOFTBELOW 79 QUOTA_NL_BSOFTBELOW
80 space (block) softlimit 80 space (block) softlimit
81 81
82 QUOTA_NL_A_DEV_MAJOR (u32) 82 QUOTA_NL_A_DEV_MAJOR (u32)
83 - major number of a device with the 83 - major number of a device with the affected filesystem
84 QUOTA_NL_A_DEV_MINOR (u32) 84 QUOTA_NL_A_DEV_MINOR (u32)
85 - minor number of a device with the 85 - minor number of a device with the affected filesystem
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