restart rep

Practice/04.10/shmat/svshm_string.h

@@ -0,0 +1,26 @@
+#include <sys/types.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/sem.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define errExit(msg)        \
+    do                      \
+    {                       \
+        perror(msg);        \
+        exit(EXIT_FAILURE); \
+    } while (0)
+
+union semun
+{ /* Used in calls to semctl() */
+    int val;
+    struct semid_ds *buf;
+    unsigned short *array;
+#if defined(__linux__)
+    struct seminfo *__buf;
+#endif
+};
+
+#define MEM_SIZE 4096

Practice/04.10/shmat/svshm_string_read.c

@@ -0,0 +1,62 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ipc.h>
+#include <sys/sem.h>
+#include <sys/shm.h>
+
+#include "svshm_string.h"
+
+int main(void)
+{
+    int semid, shmid;
+    char *addr;
+    union semun arg, dummy;
+    struct sembuf sop;
+
+    /* Create shared memory and semaphore set containing one
+       semaphore. */
+
+    shmid = shmget(IPC_PRIVATE, MEM_SIZE, IPC_CREAT | 0600);
+    if (shmid == -1)
+        errExit("shmget");
+
+    semid = semget(IPC_PRIVATE, 1, IPC_CREAT | 0600);
+    if (semid == -1)
+        errExit("semget");
+
+    /* Attach shared memory into our address space. */
+
+    addr = shmat(shmid, NULL, SHM_RDONLY);
+    if (addr == (void *)-1)
+        errExit("shmat");
+
+    /* Initialize semaphore 0 in set with value 1. */
+
+    arg.val = 1;
+    if (semctl(semid, 0, SETVAL, arg) == -1)
+        errExit("semctl");
+
+    printf("shmid = %d; semid = %d\n", shmid, semid);
+
+    /* Wait for semaphore value to become 0. */
+
+    sop.sem_num = 0;
+    sop.sem_op = 0;
+    sop.sem_flg = 0;
+
+    if (semop(semid, &sop, 1) == -1)
+        errExit("semop");
+
+    /* Print the string from shared memory. */
+
+    printf("%s\n", addr);
+
+    /* Remove shared memory and semaphore set. */
+
+    if (shmctl(shmid, IPC_RMID, NULL) == -1)
+        errExit("shmctl");
+    if (semctl(semid, 0, IPC_RMID, dummy) == -1)
+        errExit("semctl");
+
+    exit(EXIT_SUCCESS);
+}

Practice/04.10/shmat/svshm_string_write.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/sem.h>
+#include <sys/shm.h>
+
+#include "svshm_string.h"
+
+int main(int argc, char *argv[])
+{
+    int semid, shmid;
+    char *addr;
+    size_t len;
+    struct sembuf sop;
+
+    if (argc != 4)
+    {
+        fprintf(stderr, "Usage: %s shmid semid string\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    len = strlen(argv[3]) + 1; /* +1 to include trailing '\0' */
+    if (len > MEM_SIZE)
+    {
+        fprintf(stderr, "String is too big!\n");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Get object IDs from command-line. */
+    if((key = ftok("bin/sh", 'A')) = -1) errExit
+    shmid = atoi(argv[1]);
+    semid = atoi(argv[2]);
+
+    /* Attach shared memory into our address space and copy string
+       (including trailing null byte) into memory. */
+
+    addr = shmat(shmid, NULL, 0);
+    if (addr == (void *)-1)
+        errExit("shmat");
+
+    memcpy(addr, argv[3], len);
+
+    /* Decrement semaphore to 0. */
+
+    sop.sem_num = 0;
+    sop.sem_op = -1;
+    sop.sem_flg = 0;
+
+    if (semop(semid, &sop, 1) == -1)
+        errExit("semop");
+
+    exit(EXIT_SUCCESS);
+}