mmap question

dinakar.dhurjati@gmail.co · *nix forums beginner Joined: 02 Dec 2005 Posts: 4

[I posted this on unix.solaris as well, but thought people here might
know]
Hello,

I have a question on using mmap on Solaris. Any help is appreciated.

Is there a way to map multiple virtual pages to the same physical page
with in a process?

I need this capability for a research project of mine. I know how to do
this in Linux, courtesy http://lkml.org/lkml/2004/1/10/226 , but it
uses mremap, which is not
available on Solaris. Does there exist anything similar on Solaris and
other unices?

I do know how to get the same effect by mmapping an existing file at
the same offset multiple times, but I really don't want to have any
backing store for the mmap. I want to be able to do MAP_ANON and
then have it also map to a different virutal page. Any pointers?

Thanks
Dinakar

Frank Cusack · *nix forums Guru Wannabe Joined: 02 Mar 2005 Posts: 215

On 2 Dec 2005 12:10:57 -0800 dinakar.dhurjati@gmail.com wrote:

dinakar.dhurjati@gmail.co · *nix forums beginner Joined: 02 Dec 2005 Posts: 4

Tried it but it returns two differnt physical pages even when I use the
same offset in the file.

e.g. the following program returns 6 and 5 (while I want 6 and 6 ).
---------------------------------------code--------------------------------------------
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
main() {
unsigned PageSize = sysconf(_SC_PAGESIZE);
int sd;
void *pa2, *pa3, *pa;
sd = open("/dev/zero",O_CREAT|O_RDWR);
pa = mmap(0, PageSize, PROT_READ|PROT_WRITE, MAP_PRIVATE, sd, 0);
*(char *)pa = 5;
pa3 = mmap(0, PageSize, PROT_READ|PROT_WRITE, MAP_PRIVATE, sd, 0);
*(char *)pa3 = 6;
printf("%d \n",*(char *)pa3);
printf("%d \n",*(char *)pa);
}
--------------------------------------------------------------------------------------------
Thanks
Dinakar

Frank Cusack · *nix forums Guru Wannabe Joined: 02 Mar 2005 Posts: 215

Probably because of MAP_PRIVATE?

On 2 Dec 2005 14:27:16 -0800 dinakar.dhurjati@gmail.com wrote:

Google