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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-24 04:52:22 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-24 04:52:22 +0000 |
commit | 3d08cd331c1adcf0d917392f7e527b3f00511748 (patch) | |
tree | 312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man2/shmop.2 | |
parent | Adding debian version 6.7-2. (diff) | |
download | manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz manpages-3d08cd331c1adcf0d917392f7e527b3f00511748.zip |
Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'man2/shmop.2')
-rw-r--r-- | man2/shmop.2 | 507 |
1 files changed, 0 insertions, 507 deletions
diff --git a/man2/shmop.2 b/man2/shmop.2 deleted file mode 100644 index a763420..0000000 --- a/man2/shmop.2 +++ /dev/null @@ -1,507 +0,0 @@ -.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it) -.\" and Copyright 2020 Michael Kerrisk <mtk.manpages@gmail.com> -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" Modified Sun Nov 28 17:06:19 1993, Rik Faith (faith@cs.unc.edu) -.\" with material from Luigi P. Bai (lpb@softint.com) -.\" Portions Copyright 1993 Luigi P. Bai -.\" Modified Tue Oct 22 22:04:23 1996 by Eric S. Raymond <esr@thyrsus.com> -.\" Modified, 5 Jan 2002, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Modified, 19 Sep 2002, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Added SHM_REMAP flag description -.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Added notes on capability requirements -.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Language and formatting clean-ups -.\" Changed wording and placement of sentence regarding attachment -.\" of segments marked for destruction -.\" -.TH SHMOP 2 2023-10-31 "Linux man-pages 6.7" -.SH NAME -shmat, shmdt \- System V shared memory operations -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <sys/shm.h> -.P -.BI "void *shmat(int " shmid ", const void *_Nullable " shmaddr ", \ -int " shmflg ); -.BI "int shmdt(const void *" shmaddr ); -.fi -.SH DESCRIPTION -.SS shmat() -.BR shmat () -attaches the System\ V shared memory segment identified by -.I shmid -to the address space of the calling process. -The attaching address is specified by -.I shmaddr -with one of the following criteria: -.IP \[bu] 3 -If -.I shmaddr -is NULL, -the system chooses a suitable (unused) page-aligned address to attach -the segment. -.IP \[bu] -If -.I shmaddr -isn't NULL -and -.B SHM_RND -is specified in -.IR shmflg , -the attach occurs at the address equal to -.I shmaddr -rounded down to the nearest multiple of -.BR SHMLBA . -.IP \[bu] -Otherwise, -.I shmaddr -must be a page-aligned address at which the attach occurs. -.P -In addition to -.BR SHM_RND , -the following flags may be specified in the -.I shmflg -bit-mask argument: -.TP -.BR SHM_EXEC " (Linux-specific; since Linux 2.6.9)" -Allow the contents of the segment to be executed. -The caller must have execute permission on the segment. -.TP -.B SHM_RDONLY -Attach the segment for read-only access. -The process must have read permission for the segment. -If this flag is not specified, -the segment is attached for read and write access, -and the process must have read and write permission for the segment. -There is no notion of a write-only shared memory segment. -.TP -.BR SHM_REMAP " (Linux-specific)" -This flag specifies -that the mapping of the segment should replace -any existing mapping in the range starting at -.I shmaddr -and continuing for the size of the segment. -(Normally, an -.B EINVAL -error would result if a mapping already exists in this address range.) -In this case, -.I shmaddr -must not be NULL. -.P -The -.BR brk (2) -value of the calling process is not altered by the attach. -The segment will automatically be detached at process exit. -The same segment may be attached as a read and as a read-write -one, and more than once, in the process's address space. -.P -A successful -.BR shmat () -call updates the members of the -.I shmid_ds -structure (see -.BR shmctl (2)) -associated with the shared memory segment as follows: -.IP \[bu] 3 -.I shm_atime -is set to the current time. -.IP \[bu] -.I shm_lpid -is set to the process-ID of the calling process. -.IP \[bu] -.I shm_nattch -is incremented by one. -.\" -.SS shmdt() -.BR shmdt () -detaches the shared memory segment located at the address specified by -.I shmaddr -from the address space of the calling process. -The to-be-detached segment must be currently -attached with -.I shmaddr -equal to the value returned by the attaching -.BR shmat () -call. -.P -On a successful -.BR shmdt () -call, the system updates the members of the -.I shmid_ds -structure associated with the shared memory segment as follows: -.IP \[bu] 3 -.I shm_dtime -is set to the current time. -.IP \[bu] -.I shm_lpid -is set to the process-ID of the calling process. -.IP \[bu] -.I shm_nattch -is decremented by one. -If it becomes 0 and the segment is marked for deletion, -the segment is deleted. -.SH RETURN VALUE -On success, -.BR shmat () -returns the address of the attached shared memory segment; on error, -.I (void\ *)\ \-1 -is returned, and -.I errno -is set to indicate the error. -.P -On success, -.BR shmdt () -returns 0; on error \-1 is returned, and -.I errno -is set to indicate the error. -.SH ERRORS -.BR shmat () -can fail with one of the following errors: -.TP -.B EACCES -The calling process does not have the required permissions for -the requested attach type, and does not have the -.B CAP_IPC_OWNER -capability in the user namespace that governs its IPC namespace. -.TP -.B EIDRM -\fIshmid\fP points to a removed identifier. -.TP -.B EINVAL -Invalid -.I shmid -value, unaligned (i.e., not page-aligned and \fBSHM_RND\fP was not -specified) or invalid -.I shmaddr -value, or can't attach segment at -.IR shmaddr , -or -.B SHM_REMAP -was specified and -.I shmaddr -was NULL. -.TP -.B ENOMEM -Could not allocate memory for the descriptor or for the page tables. -.P -.BR shmdt () -can fail with one of the following errors: -.TP -.B EINVAL -There is no shared memory segment attached at -.IR shmaddr ; -or, -.\" The following since Linux 2.6.17-rc1: -.I shmaddr -is not aligned on a page boundary. -.SH STANDARDS -POSIX.1-2008. -.SH HISTORY -POSIX.1-2001, SVr4. -.\" SVr4 documents an additional error condition EMFILE. -.P -In SVID 3 (or perhaps earlier), -the type of the \fIshmaddr\fP argument was changed from -.I "char\ *" -into -.IR "const void\ *" , -and the returned type of -.BR shmat () -from -.I "char\ *" -into -.IR "void\ *" . -.SH NOTES -After a -.BR fork (2), -the child inherits the attached shared memory segments. -.P -After an -.BR execve (2), -all attached shared memory segments are detached from the process. -.P -Upon -.BR _exit (2), -all attached shared memory segments are detached from the process. -.P -Using -.BR shmat () -with -.I shmaddr -equal to NULL -is the preferred, portable way of attaching a shared memory segment. -Be aware that the shared memory segment attached in this way -may be attached at different addresses in different processes. -Therefore, any pointers maintained within the shared memory must be -made relative (typically to the starting address of the segment), -rather than absolute. -.P -On Linux, it is possible to attach a shared memory segment even if it -is already marked to be deleted. -However, POSIX.1 does not specify this behavior and -many other implementations do not support it. -.P -The following system parameter affects -.BR shmat (): -.TP -.B SHMLBA -Segment low boundary address multiple. -When explicitly specifying an attach address in a call to -.BR shmat (), -the caller should ensure that the address is a multiple of this value. -This is necessary on some architectures, -in order either to ensure good CPU cache performance or to ensure that -different attaches of the same segment have consistent views -within the CPU cache. -.B SHMLBA -is normally some multiple of the system page size. -(On many Linux architectures, -.B SHMLBA -is the same as the system page size.) -.P -The implementation places no intrinsic per-process limit on the -number of shared memory segments -.RB ( SHMSEG ). -.SH EXAMPLES -The two programs shown below exchange a string using a shared memory segment. -Further details about the programs are given below. -First, we show a shell session demonstrating their use. -.P -In one terminal window, we run the "reader" program, -which creates a System V shared memory segment and a System V semaphore set. -The program prints out the IDs of the created objects, -and then waits for the semaphore to change value. -.P -.in +4n -.EX -$ \fB./svshm_string_read\fP -shmid = 1114194; semid = 15 -.EE -.in -.P -In another terminal window, we run the "writer" program. -The "writer" program takes three command-line arguments: -the IDs of the shared memory segment and semaphore set created -by the "reader", and a string. -It attaches the existing shared memory segment, -copies the string to the shared memory, and modifies the semaphore value. -.P -.in +4n -.EX -$ \fB./svshm_string_write 1114194 15 \[aq]Hello, world\[aq]\fP -.EE -.in -.P -Returning to the terminal where the "reader" is running, -we see that the program has ceased waiting on the semaphore -and has printed the string that was copied into the -shared memory segment by the writer: -.P -.in +4n -.EX -Hello, world -.EE -.in -.\" -.SS Program source: svshm_string.h -The following header file is included by the "reader" and "writer" programs: -.P -.in +4n -.\" SRC BEGIN (svshm_string.h) -.EX -/* svshm_string.h -\& - Licensed under GNU General Public License v2 or later. -*/ -#include <sys/types.h> -#include <sys/ipc.h> -#include <sys/shm.h> -#include <sys/sem.h> -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -\& -#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \e - } while (0) -\& -union semun { /* Used in calls to semctl() */ - int val; - struct semid_ds * buf; - unsigned short * array; -#if defined(__linux__) - struct seminfo * __buf; -#endif -}; -\& -#define MEM_SIZE 4096 -.EE -.\" SRC END -.in -.\" -.SS Program source: svshm_string_read.c -The "reader" program creates a shared memory segment and a semaphore set -containing one semaphore. -It then attaches the shared memory object into its address space -and initializes the semaphore value to 1. -Finally, the program waits for the semaphore value to become 0, -and afterwards prints the string that has been copied into the -shared memory segment by the "writer". -.P -.in +4n -.\" SRC BEGIN (svshm_string_read.c) -.EX -/* svshm_string_read.c -\& - Licensed under GNU General Public License v2 or later. -*/ -#include <stdio.h> -#include <stdlib.h> -#include <sys/ipc.h> -#include <sys/sem.h> -#include <sys/shm.h> -\& -#include "svshm_string.h" -\& -int -main(void) -{ - int semid, shmid; - char *addr; - union semun arg, dummy; - struct sembuf sop; -\& - /* Create shared memory and semaphore set containing one - semaphore. */ -\& - shmid = shmget(IPC_PRIVATE, MEM_SIZE, IPC_CREAT | 0600); - if (shmid == \-1) - errExit("shmget"); -\& - semid = semget(IPC_PRIVATE, 1, IPC_CREAT | 0600); - if (semid == \-1) - errExit("semget"); -\& - /* Attach shared memory into our address space. */ -\& - addr = shmat(shmid, NULL, SHM_RDONLY); - if (addr == (void *) \-1) - errExit("shmat"); -\& - /* Initialize semaphore 0 in set with value 1. */ -\& - arg.val = 1; - if (semctl(semid, 0, SETVAL, arg) == \-1) - errExit("semctl"); -\& - printf("shmid = %d; semid = %d\en", shmid, semid); -\& - /* Wait for semaphore value to become 0. */ -\& - sop.sem_num = 0; - sop.sem_op = 0; - sop.sem_flg = 0; -\& - if (semop(semid, &sop, 1) == \-1) - errExit("semop"); -\& - /* Print the string from shared memory. */ -\& - printf("%s\en", addr); -\& - /* Remove shared memory and semaphore set. */ -\& - if (shmctl(shmid, IPC_RMID, NULL) == \-1) - errExit("shmctl"); - if (semctl(semid, 0, IPC_RMID, dummy) == \-1) - errExit("semctl"); -\& - exit(EXIT_SUCCESS); -} -.EE -.\" SRC END -.in -.\" -.SS Program source: svshm_string_write.c -The writer program takes three command-line arguments: -the IDs of the shared memory segment and semaphore set -that have already been created by the "reader", and a string. -It attaches the shared memory segment into its address space, -and then decrements the semaphore value to 0 in order to inform the -"reader" that it can now examine the contents of the shared memory. -.P -.in +4n -.\" SRC BEGIN (svshm_string_write.c) -.EX -/* svshm_string_write.c -\& - Licensed under GNU General Public License v2 or later. -*/ -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <sys/sem.h> -#include <sys/shm.h> -\& -#include "svshm_string.h" -\& -int -main(int argc, char *argv[]) -{ - int semid, shmid; - char *addr; - size_t len; - struct sembuf sop; -\& - if (argc != 4) { - fprintf(stderr, "Usage: %s shmid semid string\en", argv[0]); - exit(EXIT_FAILURE); - } -\& - len = strlen(argv[3]) + 1; /* +1 to include trailing \[aq]\e0\[aq] */ - if (len > MEM_SIZE) { - fprintf(stderr, "String is too big!\en"); - exit(EXIT_FAILURE); - } -\& - /* Get object IDs from command\-line. */ -\& - shmid = atoi(argv[1]); - semid = atoi(argv[2]); -\& - /* Attach shared memory into our address space and copy string - (including trailing null byte) into memory. */ -\& - addr = shmat(shmid, NULL, 0); - if (addr == (void *) \-1) - errExit("shmat"); -\& - memcpy(addr, argv[3], len); -\& - /* Decrement semaphore to 0. */ -\& - sop.sem_num = 0; - sop.sem_op = \-1; - sop.sem_flg = 0; -\& - if (semop(semid, &sop, 1) == \-1) - errExit("semop"); -\& - exit(EXIT_SUCCESS); -} -.EE -.\" SRC END -.in -.SH SEE ALSO -.BR brk (2), -.BR mmap (2), -.BR shmctl (2), -.BR shmget (2), -.BR capabilities (7), -.BR shm_overview (7), -.BR sysvipc (7) |