diff options
Diffstat (limited to 'man3/shm_open.3')
| -rw-r--r-- | man3/shm_open.3 | 121 |
1 files changed, 60 insertions, 61 deletions
diff --git a/man3/shm_open.3 b/man3/shm_open.3 index 24eddb027..c5756c475 100644 --- a/man3/shm_open.3 +++ b/man3/shm_open.3 @@ -3,7 +3,7 @@ .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" -.TH shm_open 3 2023-02-05 "Linux man-pages 6.03" +.TH shm_open 3 2023-07-20 "Linux man-pages 6.05.01" .SH NAME shm_open, shm_unlink \- create/open or unlink POSIX shared memory objects .SH LIBRARY @@ -220,37 +220,23 @@ An attempt was to made to a .I name that does not exist. -.SH VERSIONS -These functions are provided in glibc 2.2 and later. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). -.ad l -.nh .TS allbox; lbx lb lb l l l. Interface Attribute Value T{ +.na +.nh .BR shm_open (), .BR shm_unlink () T} Thread safety MT-Safe locale .TE -.hy -.ad .sp 1 -.SH STANDARDS -POSIX.1-2001, POSIX.1-2008. -.PP -POSIX.1-2001 says that the group ownership of a newly created shared -memory object is set to either the calling process's effective group ID -or "a system default group ID". -POSIX.1-2008 says that the group ownership -may be set to either the calling process's effective group ID -or, if the object is visible in the filesystem, -the group ID of the parent directory. -.SH NOTES +.SH VERSIONS POSIX leaves the behavior of the combination of .B O_RDONLY and @@ -264,6 +250,19 @@ of a dedicated .BR tmpfs (5) filesystem that is normally mounted under .IR /dev/shm . +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +glibc 2.2. +POSIX.1-2001. +.PP +POSIX.1-2001 says that the group ownership of a newly created shared +memory object is set to either the calling process's effective group ID +or "a system default group ID". +POSIX.1-2008 says that the group ownership +may be set to either the calling process's effective group ID +or, if the object is visible in the filesystem, +the group ID of the parent directory. .SH EXAMPLES The programs below employ POSIX shared memory and POSIX unnamed semaphores to exchange a piece of data. @@ -299,15 +298,15 @@ on the memory object that is shared between the two programs. #include <sys/mman.h> #include <sys/stat.h> #include <unistd.h> - +\& #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \e } while (0) - +\& #define BUF_SIZE 1024 /* Maximum size for exchanged string */ - +\& /* Define a structure that will be imposed on the shared memory object */ - +\& struct shmbuf { sem_t sem1; /* POSIX unnamed semaphore */ sem_t sem2; /* POSIX unnamed semaphore */ @@ -336,74 +335,74 @@ to tell the "send" program that it may now access the shared memory. .\" SRC BEGIN (pshm_ucase_bounce.c) .EX /* pshm_ucase_bounce.c - +\& Licensed under GNU General Public License v2 or later. */ #include <ctype.h> - +\& #include "pshm_ucase.h" - +\& int main(int argc, char *argv[]) { int fd; char *shmpath; struct shmbuf *shmp; - +\& if (argc != 2) { fprintf(stderr, "Usage: %s /shm\-path\en", argv[0]); exit(EXIT_FAILURE); } - +\& shmpath = argv[1]; - +\& /* Create shared memory object and set its size to the size of our structure. */ - +\& fd = shm_open(shmpath, O_CREAT | O_EXCL | O_RDWR, 0600); if (fd == \-1) errExit("shm_open"); - +\& if (ftruncate(fd, sizeof(struct shmbuf)) == \-1) errExit("ftruncate"); - +\& /* Map the object into the caller\[aq]s address space. */ - +\& shmp = mmap(NULL, sizeof(*shmp), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (shmp == MAP_FAILED) errExit("mmap"); - +\& /* Initialize semaphores as process\-shared, with value 0. */ - +\& if (sem_init(&shmp\->sem1, 1, 0) == \-1) errExit("sem_init\-sem1"); if (sem_init(&shmp\->sem2, 1, 0) == \-1) errExit("sem_init\-sem2"); - +\& /* Wait for \[aq]sem1\[aq] to be posted by peer before touching shared memory. */ - +\& if (sem_wait(&shmp\->sem1) == \-1) errExit("sem_wait"); - +\& /* Convert data in shared memory into upper case. */ - +\& for (size_t j = 0; j < shmp\->cnt; j++) shmp\->buf[j] = toupper((unsigned char) shmp\->buf[j]); - +\& /* Post \[aq]sem2\[aq] to tell the peer that it can now access the modified data in shared memory. */ - +\& if (sem_post(&shmp\->sem2) == \-1) errExit("sem_post"); - +\& /* Unlink the shared memory object. Even if the peer process is still using the object, this is okay. The object will be removed only after all open references are closed. */ - +\& shm_unlink(shmpath); - +\& exit(EXIT_SUCCESS); } .EE @@ -429,13 +428,13 @@ on standard output. .\" SRC BEGIN (pshm_ucase_send.c) .EX /* pshm_ucase_send.c - +\& Licensed under GNU General Public License v2 or later. */ #include <string.h> - +\& #include "pshm_ucase.h" - +\& int main(int argc, char *argv[]) { @@ -443,54 +442,54 @@ main(int argc, char *argv[]) char *shmpath, *string; size_t len; struct shmbuf *shmp; - +\& if (argc != 3) { fprintf(stderr, "Usage: %s /shm\-path string\en", argv[0]); exit(EXIT_FAILURE); } - +\& shmpath = argv[1]; string = argv[2]; len = strlen(string); - +\& if (len > BUF_SIZE) { fprintf(stderr, "String is too long\en"); exit(EXIT_FAILURE); } - +\& /* Open the existing shared memory object and map it into the caller\[aq]s address space. */ - +\& fd = shm_open(shmpath, O_RDWR, 0); if (fd == \-1) errExit("shm_open"); - +\& shmp = mmap(NULL, sizeof(*shmp), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (shmp == MAP_FAILED) errExit("mmap"); - +\& /* Copy data into the shared memory object. */ - +\& shmp\->cnt = len; memcpy(&shmp\->buf, string, len); - +\& /* Tell peer that it can now access shared memory. */ - +\& if (sem_post(&shmp\->sem1) == \-1) errExit("sem_post"); - +\& /* Wait until peer says that it has finished accessing the shared memory. */ - +\& if (sem_wait(&shmp\->sem2) == \-1) errExit("sem_wait"); - +\& /* Write modified data in shared memory to standard output. */ - +\& write(STDOUT_FILENO, &shmp\->buf, len); write(STDOUT_FILENO, "\en", 1); - +\& exit(EXIT_SUCCESS); } .EE |