mmap_peer(), mmap64_peer()

Arguments:

pid

The ID of the process in which you want to map memory.

addr

NULL, or a pointer to where you want the object to be mapped in the specified process's address space.

len

The number of bytes to map into the specified process's address space. Note that this value can't be 0.

prot

The access capabilities that you want to use for the memory region being mapped. You can combine at least the following protection bits, as defined in <sys/mman.h>:

• PROT_EXEC — the region can be executed.
  Note:

  To successfully use this flag, your process must have the PROCMGR_AID_PROT_EXEC ability enabled if fd is not NOFD and PROT_WRITE is not included. Otherwise, it requires PROCMGR_AID_PROT_WRITE_AND_EXEC. For more information, see procmgr_ability().
• PROT_NOCACHE — disable caching of the region (e.g., so it can be used to access dual-ported memory).
  Note:

  On ARM targets, PROT_NOCACHE causes RAM to be mapped as normal noncached, but non-RAM to be mapped as strongly ordered device memory. For finer control, see shm_ctl_special().
• PROT_NONE — the region can't be accessed.
• PROT_READ — the region can be read.
• PROT_WRITE — the region can be written.

flags

Flags that specify further information about handling the mapped region. For detailed information about the flags, see mmap().

fd

The file descriptor for a shared memory object, or NOFD if you're mapping physical memory.

off

The offset into shared memory of the location that you want to start mapping.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The mmap_peer() function maps a region within the object of the specified process ID beginning at off and continuing for len into the address space, and returns the location.

The address returned by mmap_peer() is valid only in the context of the process pid.

The target process can:

• use mprotect() to increase permissions on whatever was mapped in, if the file descriptor allows those permissions
• unmap the memory
• use fork() to duplicate the mapping unbeknownst to the caller of mmap_peer()

Returns:

The address of the mapped-in object, or MAP_FAILED if an error occurred (errno is set).

Errors:

In addition to the errno codes set by mmap(), the following can be set:

ESRCH

The process pid doesn't exist, is loading, or is terminating.

Example:

The following example forks into parent and child process, and the parent process waits for the child process to terminate. The child process does the following:

• performs mmap_peer() and stores the returned address
• checks to see if the mmap_peer() function failed
• performs munmap_peer() and verifies the return value

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <process.h>
#include <sys/mman.h>

int main(int argc, char *argv[])
{
   pid_t pid;
   pid_t parent_pid;
   char buff[256];
   const int mmap_len = 4096;

   parent_pid = getpid();
 
   pid = fork();
   assert( pid != -1);

   if( pid == 0 ) {
      /* This is the child process */

      void *ptr, *old_ptr;
      int ret;
      int failed;

      failed = 0;

      old_ptr = mmap_peer( parent_pid, 0, mmap_len, PROT_READ | PROT_WRITE,
                           MAP_SHARED, NOFD, 0);
      if (old_ptr == MAP_FAILED) {
         SPRNT( buff, sizeof(buff), "mmap_peer failed (errno %d)", errno);
         failed++;
      }
  
      if (!failed) {
         ret = munmap_peer(parent_pid, old_ptr, mmap_len);

         if ( ret == -1 ) {
             SPRNT( buff, sizeof(buff), "munmap_peer failed (errno %d)", errno);
             failed++;
         }
      }
   } else {
      /* This is the parent process */
      wait(NULL);
   }
     
   return EXIT_SUCCESS;
}

Classification:

mmap_peer() is QNX OS; mmap64_peer() is Large-file support