mem_offset(), mem

Synopsis:

#include <sys/mman.h>

int mem_offset( const void * addr,
                int fd,
                size_t length,
                off_t * offset,
                size_t * contig_len );

int mem_offset64( const void * addr,
                  int fd,
                  size_t length,
                  off64_t * offset,
                  size_t * contig_len );

Arguments:

addr: The virtual address of the memory block whose physical address you want to get. This address doesn't have to be page-aligned (i.e., a multiple of PAGESIZE) because the function reports the physical address that backs the virtual address.
fd: This must be NOFD, or the function fails.
length: The length of the memory block that you want the location of.
offset: NULL, or a pointer to a location for storing the physical address that the virtual address (addr) maps to.
contig_len: NULL, or a pointer to a location for storing either length or the length of the physically contiguous block of memory that starts at addr, whichever is smaller.

Library:

libc

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

Description:

The mem_offset() and mem_offset64() functions set the variable pointed to by offset to the physical address of addr. The length of the physically contiguous block of memory at addr is written into the variable pointed to by contig_len if this argument is not NULL.

Note:

The mem_offset64() function is a large-file support version of mem_offset(). The large-file support functions and data types appear in the namespace only if you define _LARGEFILE64_SOURCE when you compile your code. For more information, see “Classification” in “What's in a Function Description?”.
If the physical address isn't a valid off_t value, mem_offset() will fail with errno set to EOVERFLOW. This is typically the case with many ARM systems, and you should use mem_offset64() to get the physical address.
These functions also cause the initial copying or zero-filling of MAP_PRIVATE or MAP_ANON pages.
For best performance results, you should cache the result of mem_offset(), rather than repeatedly call the function for a given virtual address.

These functions succeed only if the memory in question is locked (either explicitly with an mlock() or mlockall() call, or implicitly, such as when an entire process or system is fully locked).

Returns:

0: Success.
-1: An error occurred (errno is set).

Errors:

EACCES: The process hasn't mapped memory at the given address addr, or the address is of MAP_LAZY pages that aren't yet memory-resident.
EAGAIN: The memory isn't locked. The returned offset might correspond to the physical address associated with the given virtual one, but don't rely on it for any functionality. The location that contig_len points to might also be updated. These values are transient and are reported back as a debugging/testing aid only.
ENODEV: The file descriptor fd isn't NOFD.
EOVERFLOW: This error is specific to mem_offset() and is returned when the address is too large for the 32-bit off_t; use mem_offset64() instead.

Examples:

off64_t offset;

if (mem_offset64(addr, NOFD, 1, &offset, NULL) == -1)
{
  /* Error */
}
else
{
  /* offset contains the physical address of the memory
     mapped at addr. */
}

Classification:

mem_offset() is QNX Neutrino; mem_offset64() is Large-file support

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes

mem_offset(), mem_offset64()