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Annotated edit history of semctl(2) version 2, including all changes. View license author blame.
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1 perry 1 !!NAME
2 semctl - semaphore control operations
3 !!SYNOPSIS
2 PerryLorier 4 __#include <sys/types.h>__
5 __#include <sys/ipc.h>__
6 __#include <sys/sem.h>__
1 perry 7
2 PerryLorier 8 __int semctl(int __''semid''__, int __''semnum''__, int __''cmd''__, ...);__
1 perry 9 !!DESCRIPTION
10
11
2 PerryLorier 12 The function performs the control operation specified by ''cmd'' on the semaphore set (or on the ''semnum''-th semaphore of the set) identified by ''semid''. The first
13 semaphore of the set is indicated by a value __0__ for ''semnum''.
1 perry 14
15
16 Legal values for ''cmd'' are
2 PerryLorier 17 ;__IPC_STAT__: Copy info from the semaphore set data structure into the structure pointed to by ''arg''__.buf__. The argument ''semnum'' is ignored. The calling process must have read access privileges on the semaphore set.
18 ;__IPC_SET__: Write the values of some members of the __semid_ds__ structure pointed to by ''arg''__.buf__ to the semaphore set data structure, updating also its
19 __sem_ctime__ member. Considered members from the user supplied __struct semid_ds__ pointed to by ''arg''__.buf__ are
20 __ sem_perm.uid__
21 __sem_perm.gid__
22 __sem_perm.mode__ /* only lowest 9-bits */
23 ;:The calling process effective user-ID must be one among super-user, creator or owner of the semaphore set. The argument ''semnum'' is ignored.
1 perry 24
2 PerryLorier 25 ;__IPC_RMID__: Remove immediately the semaphore set and its data structures awakening all waiting processes (with an error return and __errno__ set to __EIDRM__). The calling process effective user-ID must be one among super-user, creator or owner of the semaphore set. The argument ''semnum'' is ignored.
1 perry 26
2 PerryLorier 27 ;__GETALL__: Return __semval__ for all semaphores of the set into ''arg''__.array__. The argument ''semnum'' is ignored. The calling process must have read access privileges on the semaphore set.
1 perry 28
2 PerryLorier 29 ;__GETNCNT__: The system call returns the value of __semncnt__ for the ''semnum''-th semaphore of the set (i.e. the number of processes waiting for an increase of __semval__ for the ''semnum''-th semaphore of the set). The calling process must have read access privileges on the semaphore set.
1 perry 30
2 PerryLorier 31 ;__GETPID__: The system call returns the value of __sempid__ for the ''semnum''-th semaphore of the set (i.e. the pid of the process that executed the last __semop__ call for the ''semnum''-th semaphore of the set). The calling process must have read access privileges on the semaphore
1 perry 32 set.
33
2 PerryLorier 34 ;__GETVAL__: The system call returns the value of __semval__ for the ''semnum''-th semaphore of the set. The calling process must have read access privileges on the semaphore set.
1 perry 35
2 PerryLorier 36 ;__GETZCNT__: The system call returns the value of __semzcnt__ for the ''semnum''-th semaphore of the set (i.e. the number of processes waiting for __semval__ of the ''semnum''-th semaphore of the set to become 0). The calling process must have read access privileges on the semaphore set.
1 perry 37
2 PerryLorier 38 ;__SETALL__: Set __semval__ for all semaphores of the set using ''arg''__.array__'','' updating also the __sem_ctime__ member of the __semid_ds__ structure associated to the set. Undo entries are cleared for altered semaphores in all processes. Processes sleeping on the wait queue are awakened if some __semval__ becomes 0 or increases. The argument ''semnum'' is ignored. The calling process must have alter access privileges on the semaphore set.
1 perry 39
2 PerryLorier 40 ;__SETVAL__: Set the value of __semval__ to ''arg''__.val__ for the ''semnum''-th semaphore of the set, updating also the __sem_ctime__ member of the __semid_ds__ structure associated to the set. Undo entry is cleared for altered semaphore in all processes. Processes sleeping on the wait queue are awakened if __semval__ becomes 0 or increases. The calling process must have alter access privileges on the semaphore set.
1 perry 41
42 !!RETURN VALUE
2 PerryLorier 43 On fail the system call returns __-1__ with __errno__ indicating the error. Otherwise the system call returns a nonnegative value depending on ''cmd'' as follows:
1 perry 44
2 PerryLorier 45 ;__GETNCNT__: The value of __semncnt__.
1 perry 46
2 PerryLorier 47 ;__GETPID__: the value of __sempid__.
1 perry 48
2 PerryLorier 49 ;__GETVAL__: the value of __semval__.
1 perry 50
2 PerryLorier 51 ;__GETZCNT__: the value of __semzcnt__.
1 perry 52
53 !!ERRORS
2 PerryLorier 54 For a failing return, __errno__ will be set to one among the following values:
55 ;[EACCES]: The calling process has no access permissions needed to execute ''cmd''.
56 ;[EFAULT]: The address pointed to by ''arg''__.buf__ or ''arg''__.array__ isn't accessible.
57 ;[EIDRM]: The semaphore set was removed.
58 ;[EINVAL]: Invalid value for ''cmd'' or ''semid''.
59 ;[EPERM]: The argument ''cmd'' has value __IPC_SET__ or __IPC_RMID__ but the calling process effective user-ID has insufficient privileges to execute the
1 perry 60 command.
2 PerryLorier 61 ;[ERANGE]: The argument ''cmd'' has value __SETALL__ or __SETVAL__ and the value to which __semval__ has to be set (for some semaphore of the set) is less than 0 or
62 greater than the implementation value __SEMVMX__.
1 perry 63 !!NOTES
2 PerryLorier 64 The __IPC_INFO__, __SEM_STAT__ and __SEM_INFO__ control calls are used by the ipcs(8) program to provide information on allocated resources. In the future
65 these can be modified as needed or moved to a proc file system interface.
1 perry 66
2 PerryLorier 67 Various fields in a ''struct semid_ds'' were shorts under Linux 2.2 and have become longs under Linux 2.4. To take advantage of this, a recompilation under glibc-2.1.91 or later should suffice. (The kernel distinguishes old and new calls by a IPC_64 flag in ''cmd''.)
1 perry 68
2 PerryLorier 69 The following system limit on semaphore sets affects a __semctl__ call:
1 perry 70
2 PerryLorier 71 ;__SEMVMX__: Maximum value for __semval__: implementation dependent (32767).
1 perry 72
73 !!CONFORMING TO
2 PerryLorier 74 SVr4, SVID. SVr4 documents more error conditions [EINVAL] and [EOVERFLOW].
1 perry 75
76 !!SEE ALSO
2 PerryLorier 77 ipc(5), shmget(2), shmat(2), shmdt(2)
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