Mastering Linux Kernel Development

Allocating shared memory

shmget() system call is invoked by a process to get an IPC identifier for a shared memory region; if the region does not exists, it creates one:

int shmget(key_t key, size_t size, int shmflg);

This function returns the identifier of the shared memory segment corresponding to the value contained in the key parameter. If other processes intend to use an existing segment, they can use the segment's key value when looking for its identifier. A new segment is however created if the key parameter is unique or has the value IPC_PRIVATE. size indicates the number of bytes that needs to be allocated, as segments are allocated as memory pages. The number of pages to be allocated is obtained by rounding off the size value to ...