Though somewhat off-topic, I am trying to port our simulation/control/data_acq system
to RTLinux.
Key to the success of this endeavor, is the capability of having one process able to
read/write
into the process space of another. In the example provided I can both mmap() and
read()/write()
/proc on our current platform. On Linux 2.4.1 (RH7.1) however, neither worked.
A couple of years ago, when I first tried this with RH5.2 (I don't remember the Linux
version)
I remember seeing a similar (if not identical) disclaimer to what's in the current
proc(5)
manpage. The last sentence gave me hope the capability I was seeking was to be
implemented
imminently.
mem This is not the same as the mem (1:1) device, despite the fact that it has the
same device numbers. The /dev/mem device is the physical memory before any
address translation is done, but the mem file here is the memory of the
process
that accesses it. This cannot be mmap(2)'ed currently, and will not be until
a
general mmap(2) is added to the kernel. (This might have happened by the
time
you read this.)
Either Linux can in some form support this and I'm doing something wrong (and the
documentation
is out-of-date); or it is currently not yet possible through /proc.
Thank you for taking the time to read this note. Any help or pointers would be very
much
appreciated (I hope someone else has crossed this bridge before me).
Dean W. Anneser
Software Engineering Fellow
Real-Time Test Systems
Pratt & Whitney Aircraft
400 Main St., m.s. 161-05
East Hartford, CT 06108
email: [EMAIL PROTECTED]
phone: 860.565.9372 fax: 860.557.3482
"One test result is worth one thousand expert opinions" - Wernher von Braun
example code:
Use mmap.c to view the parameter iii in program tst.c, while tst.c is
running in background:
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= mmap.c =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/utsname.h>
#define MMAP 1
#define RW 2
void main(int argc, char *argv[])
{
int i, j, k;
int iii = 0;
int *piii;
char tmp[256];
int fd;
caddr_t p;
struct utsname sysname;
struct stat statinfo;
int bytes_read = 0;
int page_base;
int page_offset;
int page_size;
int pid = 0;
int addr = 0;
int use = MMAP;
int ret = 0;
int argi = 0;
while (++argi < argc)
{
if (strcmp(argv[argi], "-pid") == 0)
sscanf(argv[++argi], "%d", &pid);
else if (strcmp(argv[argi], "-addr") == 0)
sscanf(argv[++argi], "%x", &addr);
else if (strcmp(argv[argi], "-use") == 0)
{
if (strcmp(argv[++argi], "mmap") == 0)
use = MMAP;
else
use = RW;
}
else
{
printf("unrecognized option: %s\n", argv[argi]);
printf("usage: mmap -pid <pid> -addr <addr>\n");
exit(1);
}
}
uname(&sysname);
if ((pid == 0) || (addr == 0))
{
printf("usage: mmap -pid <pid> -addr <addr>\n");
exit(1);
}
if (strcmp(sysname.sysname, "Linux") == 0)
sprintf(tmp, "/proc/%d/mem", pid); /* Linux */
else
sprintf(tmp, "/proc/%d/as", pid); /* PowerMAX_OS or SunOS */
if ((fd = open(tmp, O_RDWR)) == -1)
{
printf("open failure on %s\n", tmp);
exit(1);
}
if (fstat(fd, &statinfo) == -1)
{
printf("fstat failed on %s\n", tmp);
exit(1);
}
if (use == RW)
{
while (bytes_read != -1)
{
if ((ret = lseek(fd, addr, SEEK_SET)) == -1)
{
printf("lseek() error = %d\n", ret);
exit(1);
}
if ((bytes_read = read(fd, &iii, sizeof(int))) <= 0)
{
printf("read() error = %d\n", bytes_read);
exit(1);
}
printf("bytes_read = %d, iii = %d\r", bytes_read, iii);
fflush(stdout);
sleep(1);
}
}
else
{
page_size = getpagesize();
page_base = (addr / page_size) * page_size;
page_offset = addr % page_size;
if ((p = (caddr_t)mmap(0, page_size, (PROT_READ | PROT_WRITE), MAP_SHARED, fd,
page_base)) == (caddr_t)-1)
{
printf("mmap failure on %s\n", tmp);
printf(" statinfo.st_size == %d\n", statinfo.st_size);
printf(" page_size == %#x\n", page_size);
printf(" page_base == %#x\n", page_base);
printf(" page_offset == %#x\n", page_offset);
perror((char *)0);
close(fd);
exit(1);
}
piii = (int *)(p + page_offset);
while (1)
{
printf("iii = %d\r", *piii);
fflush(stdout);
sleep(1);
}
}
}
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= tst.c =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
#include <stdio.h>
int iii, jjj, kkk;
void main()
{
iii = jjj = kkk = 0;
while (1)
{
iii += 1;
jjj += 1;
kkk += 1;
printf("iii = %d; jjj = %d; kkk = %d\n", iii, jjj, kkk);
fflush(stdout);
sleep(1);
}
}
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Makefile =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
all: mmap tst
%: %.c
cc -g $(LFLAGS) -o $@ $<
clean:
rm mmap tst
mmap: mmap.c
tst: tst.c
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= running =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
/home/anneser/mmap> nm tst | grep iii
08049658 B iii
/home/anneser/mmap> ./tst > tst.out &
[1] 1356
/home/anneser/mmap> ./mmap -pid 1356 -addr 0x08049658 -use mmap
mmap failure on /proc/1356/mem
statinfo.st_size == 0
page_size == 0x1000
page_base == 0x8049000
page_offset == 0x658
No such device
/home/anneser/mmap> ./mmap -pid 1356 -addr 0x08049658 -use rw
read() error = -1
/home/anneser/mmap>
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