SHMAT(2) BSD Programmer's Manual SHMAT(2)
shmat, shmdt - map/unmap shared memory
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> void * shmat(int shmid, const void *shmaddr, int shmflg); int shmdt(const void *shmaddr);
shmat() maps the shared memory segment associated with the shared memory identifier shmid into the address space of the calling process. The ad- dress at which the segment is mapped is determined by the shmaddr parame- ter. If it is equal to 0, the system will pick an address itself. Other- wise, an attempt is made to map the shared memory segment at the address shmaddr specifies. If SHM_RND is set in shmflg, the system will round the address down to a multiple of SHMLBA bytes (SHMLBA is defined in <sys/shm.h>). A shared memory segment can be mapped read-only by specifying the SHM_RDONLY flag in shmflg. shmdt() unmaps the shared memory segment that is currently mapped at shmaddr from the calling process' address space. shmaddr must be a value returned by a prior shmat() call. A shared memory segment will remain ex- istent until it is removed by a call to shmctl(2) with the IPC_RMID com- mand.
shmat() returns the address at which the shared memory segment has been mapped into the calling process' address space when successful, shmdt() returns 0 on successful completion. Otherwise, a value of -1 is returned, and the global variable errno is set to indicate the error.
shmat() will fail if: [EACCES] The calling process has no permission to access this shared memory segment. [ENOMEM] There is not enough available data space for the calling process to map the shared memory segment. [EINVAL] shmid is not a valid shared memory identifier. shmaddr specifies an illegal address. [EMFILE] The number of shared memory segments has reached the system-wide limit. shmdt() will fail if: [EINVAL] shmaddr is not the start address of a mapped shared memory segment.
ipcrm(1), ipcs(1), mmap(2), shmctl(2), shmget(2) MirOS BSD #10-current August 17, 1995 1
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