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shmat(2) [freebsd man page]

SHMAT(2)						      BSD System Calls Manual							  SHMAT(2)

NAME
shmat, shmdt -- attach or detach shared memory LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> void * shmat(int shmid, const void *addr, int flag); int shmdt(const void *addr); DESCRIPTION
The shmat() system call attaches the shared memory segment identified by shmid to the calling process's address space. The address where the segment is attached is determined as follows: o If addr is 0, the segment is attached at an address selected by the kernel. o If addr is nonzero and SHM_RND is not specified in flag, the segment is attached the specified address. o If addr is specified and SHM_RND is specified, addr is rounded down to the nearest multiple of SHMLBA. The shmdt() system call detaches the shared memory segment at the address specified by addr from the calling process's address space. RETURN VALUES
Upon success, shmat() returns the address where the segment is attached; otherwise, -1 is returned and errno is set to indicate the error. The shmdt() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The shmat() system call will fail if: [EINVAL] No shared memory segment was found corresponding to shmid. [EINVAL] The addr argument was not an acceptable address. The shmdt() system call will fail if: [EINVAL] The addr argument does not point to a shared memory segment. SEE ALSO
shmctl(2), shmget(2) BSD
August 2, 1995 BSD

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SHMAT(2)						      BSD System Calls Manual							  SHMAT(2)

NAME
shmat, shmdt -- map/unmap shared memory SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> void * shmat(int shmid, void *shmaddr, int shmflg); int shmdt(void *shmaddr); DESCRIPTION
shmat() maps the shared memory segment associated with the shared memory identifier shmid into the address space of the calling process. The address at which the segment is mapped is determined by the shmaddr parameter. If it is equal to 0, the system will pick an address itself. Otherwise, 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 existant until it is removed by a call to shmctl(2) with the IPC_RMID command. RETURN VALUES
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. ERRORS
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. SEE ALSO
shmctl(2), shmget(2), mmap(2) BSD
August 17, 1995 BSD

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