mmap, munmap - map or unmap files or devices into memory
#include <unistd.h> #include <sys/mman.h>
void * mmap(void *start, size_t length, int prot , int flags, int fd, off_t offset);
int munmap(void *start, size_t length);
The mmap function asks to map length bytes starting at offset offset from the file (or other object) specified by the file descriptor fd into memory, preferably at address start. This latter address is a hint only, and is usually specified as 0. The actual place where the object is mapped is returned by mmap. The prot argument describes the desired memory protection (and must not conflict with the open mode of the file). It has bits
The flags parameter specifies the type of the mapped object, mapping options and whether modifications made to the mapped copy of the page are private to the process or are to be shared with other references. It has bits
You must specify exactly one of MAP_SHARED and MAP_PRIVATE.
The above three flags are described in POSIX.1b (formerly POSIX.4). Linux also knows about MAP_DENYWRITE, MAP_EXECUTABLE, MAP_NORESERVE, MAP_LOCKED, MAP_GROWSDOWN and MAP_ANON(YMOUS).
offset should ordinarily be a multiple of the page size returned by getpagesize(2).
Memory mapped by mmap is preserved across fork(2), with the same attributes.
The munmap system call deletes the mappings for the specified address range, and causes further references to addresses within the range to generate invalid memory references. The region is also automatically unmapped when the process is terminated. On the other hand, closing the file descriptor does not unmap the region.
Use of a mapped region can result in these signals:
SVr4, POSIX.1b (formerly POSIX.4), 4.4BSD. Svr4 documents additional error codes ENXIO and ENODEV.
lib/main.php:944: Notice: PageInfo: Cannot find action page