projects / GitHub / mt8127 / android_kernel_alcatel_ttab.git / blame
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1 | |
| 2 | Quota subsystem | |
| 3 | =============== | |
| 4 | ||
| 5 | Quota subsystem allows system administrator to set limits on used space and | |
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6 | number of used inodes (inode is a filesystem structure which is associated with |
| 7 | each file or directory) for users and/or groups. For both used space and number | |
| 8 | of used inodes there are actually two limits. The first one is called softlimit | |
| 9 | and the second one hardlimit. An user can never exceed a hardlimit for any | |
| 10 | resource (unless he has CAP_SYS_RESOURCE capability). User is allowed to exceed | |
| 11 | softlimit but only for limited period of time. This period is called "grace | |
| 12 | period" or "grace time". When grace time is over, user is not able to allocate | |
| 13 | more space/inodes until he frees enough of them to get below softlimit. | |
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14 | |
| 15 | Quota limits (and amount of grace time) are set independently for each | |
| 16 | filesystem. | |
| 17 | ||
| 18 | For more details about quota design, see the documentation in quota-tools package | |
| 19 | (http://sourceforge.net/projects/linuxquota). | |
| 20 | ||
| 21 | Quota netlink interface | |
| 22 | ======================= | |
| 23 | When user exceeds a softlimit, runs out of grace time or reaches hardlimit, | |
| 24 | quota subsystem traditionally printed a message to the controlling terminal of | |
| 25 | the process which caused the excess. This method has the disadvantage that | |
| 26 | when user is using a graphical desktop he usually cannot see the message. | |
| 27 | Thus quota netlink interface has been designed to pass information about | |
| 28 | the above events to userspace. There they can be captured by an application | |
| 29 | and processed accordingly. | |
| 30 | ||
| 31 | The interface uses generic netlink framework (see | |
| 32 | http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more | |
| 33 | details about this layer). The name of the quota generic netlink interface | |
| 34 | is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>. | |
| 35 | Currently, the interface supports only one message type QUOTA_NL_C_WARNING. | |
| 36 | This command is used to send a notification about any of the above mentioned | |
| 37 | events. Each message has six attributes. These are (type of the argument is | |
| 38 | in 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 | |
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56 | - four warnings are also defined for the event when user stops |
| 57 | exceeding some limit: | |
| 58 | QUOTA_NL_IHARDBELOW - inode hardlimit | |
| 59 | QUOTA_NL_ISOFTBELOW - inode softlimit | |
| 60 | QUOTA_NL_BHARDBELOW - space (block) hardlimit | |
| 61 | QUOTA_NL_BSOFTBELOW - space (block) softlimit | |
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62 | QUOTA_NL_A_DEV_MAJOR (u32) |
| 63 | - major number of a device with the affected filesystem | |
| 64 | QUOTA_NL_A_DEV_MINOR (u32) | |
| 65 | - minor number of a device with the affected filesystem |