mmap/t_mmap.c

+/* t_mmap.c
+
+   Demonstrate the use of mmap() to create a shared file mapping.
+*/
 #include <sys/mman.h>
 #include <fcntl.h>
 #include "tlpi_hdr.h"
 
 #define MEM_SIZE 10
 
 int
 main(int argc, char *argv[])
 {
     char *addr;
     int fd;
 
     if (argc < 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s file [new-value]\n", argv[0]);
 
     fd = open(argv[1], O_RDWR);
     if (fd == -1)
         errExit("open");
 
     addr = mmap(NULL, MEM_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
     if (addr == MAP_FAILED)
         errExit("mmap");
 
     if (close(fd) == -1)                /* No longer need 'fd' */
         errExit("close");
 
     printf("Current string=%.*s\n", MEM_SIZE, addr);
                         /* Secure practice: output at most MEM_SIZE bytes */
 
     if (argc > 2) {                     /* Update contents of region */
         if (strlen(argv[2]) >= MEM_SIZE)
             cmdLineErr("'new-value' too large\n");
 
         memset(addr, 0, MEM_SIZE);      /* Zero out region */
         strncpy(addr, argv[2], MEM_SIZE - 1);
         if (msync(addr, MEM_SIZE, MS_SYNC) == -1)
             errExit("msync");
 
         printf("Copied \"%s\" to shared memory\n", argv[2]);
     }
 
     exit(EXIT_SUCCESS);
 }