Get the physical address and length of a mapped memory block
Note:
The QNX Neutrino implementation doesn't follow the expected POSIX behavior,
because this function does not return an offset within the object, but instead returns a direct
physical address.
Synopsis:
#include <sys/mman.h>
int posix_mem_offset( const void *addr,
size_t len,
off_t *off,
size_t *contig_len,
int *filedes );
int posix_mem_offset64( const void *addr,
size_t len,
off64_t *off,
size_t *contig_len,
int *filedes );
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.
- len
- The length of the memory block that you want the location of.
- off
- 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 the value
of len or the length of the physically contiguous block of memory
that starts at addr, whichever is smaller.
- filedes
- A pointer to a location for storing the file descriptor used to establish
the mapping that contains addr.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The posix_mem_offset() and posix_mem_offset64() functions set
the variable pointed to by off to the physical address
of the memory block currently mapped at 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
posix_mem_offset64() function is a large-file support version of
posix_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?”.
These functions support typed memory, shared memory, and memory-mapped files, but not anonymous
memory.
Returns:
0 on success, -1 if an error occurred (errno is set).
Errors:
- EACCES
- The process hasn't mapped a memory object at the given address addr.
- EOVERFLOW
- This error is specific to posix_mem_offset() and is returned when the address is too large for the
32-bit off_t; use posix_mem_offset64() instead.
Classification:
posix_mem_offset() is
POSIX 1003.1 TYM;
posix_mem_offset64() is
Large-file support
| Safety: |
|
|---|
| Cancellation point |
No |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
Yes |