Open Dev Mem C

1. Can't Open /dev/mem
2. Can't Open '/dev/mem' No Such File Or Directory

Because the addresses move, and because /dev/mem direct physical memory access requires root permissions, there is a simpler interface file /dev/gpiomem.

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An example of using shared memory in a POSIX system. #c #linux #shmem #shm_open #shared-memory

use-shared-memory-1.c

// Note: Link with -lrt

#include<stdio.h>

#include<stdlib.h>

#include<sys/mman.h>

#include<sys/stat.h>/* For mode constants */

#include<fcntl.h>/* For O_* constants */

#include<unistd.h>

#include<string.h>

#include<assert.h>

intmain(int argc, char **argv) {

int oflags=O_RDWR;

int opt;

while ((opt = getopt(argc, argv, 'c')) != -1) {

switch (opt) {

case'c': /* create it */

oflags = O_RDWR | O_CREAT;

break;

default: /* '?' */

fprintf(stderr, 'Usage: %s -[c]n', argv[0]);

exit(EXIT_FAILURE);

}

}

off_t length = 2 * 1024;

char *name = '/malex.hello03.01';

int fd = shm_open(name, oflags, 0644 );

ftruncate(fd, length);

fprintf(stderr,'Shared Mem Descriptor: fd=%dn', fd);

assert (fd>0);

u_char *ptr = (u_char *) mmap(NULL, length, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

fprintf(stderr, 'Shared Memory Address: %p [0.%lu]n', ptr, length-1);

fprintf(stderr, 'Shared Memory Path: /dev/shm/%sn', name );

assert (ptr);

char *msg = 'hello world!!n';

strcpy((char*)ptr,msg);

close(fd);

exit(0);

}

use-shared-memory-2.c

#include<stdio.h>

#include<stdlib.h>

#include<sys/mman.h>

#include<sys/stat.h>/* For mode constants */

#include<fcntl.h>/* For O_* constants */

#include<unistd.h>

#include<string.h>

#include<assert.h>

intmain(int argc, char **argv) {

int oflags=O_RDWR;

int i;

char *name = '/malex.hello03.01';

int fd = shm_open(name, oflags, 0644 );

fprintf(stderr,'Shared Mem Descriptor: fd=%dn', fd);

assert (fd>0);

struct stat sb;

fstat(fd, &sb);

off_t length = sb.st_size ;

u_char *ptr = (u_char *) mmap(NULL, length, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

fprintf(stderr, 'Shared Mem Address: %p [0.%lu]n', ptr, length-1);

assert (ptr);

// hexdump first 100 bytes

fprintf(stdout,'First 100 bytes:n');

for(i=0; i<100; i++)

fprintf(stdout, '%02X%s', ptr[i], (i%2524)?('n'):('') );

// change 1st byte

ptr[ 0 ] = 'H' ;

close(fd);

exit(0);

}

commented Mar 14, 2020

Can't Open /dev/mem

What does 0644 mean in shm_open(name, oflags, 0644 );?

commented Mar 14, 2020

@pharapeti it is the ownership mode, just like in the open system call Now For the activation of KMSpico Windows 10 we are using. KMSpico Windows 10 Activator Key Generator – KMSAuto:and Is the most popular and most downloaded software on internet as. It is basically used for activating windows for lifetime. Windows 10 enterprise product key generator online.

Can't Open '/dev/mem' No Such File Or Directory

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