88 lines
2.3 KiB
C
88 lines
2.3 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <fcntl.h>
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#include <sys/shm.h>
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#include <sys/stat.h>
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#include <sys/mman.h>
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#include <sys/types.h>
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#include <errno.h>
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void display(char* prog, char* bytes, int n);
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int main(void)
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{
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const char* name = "/shm-example"; // file name
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const int SIZE = 4096; // file size
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const char* message0 = "Studying ";
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const char* message1 = "Operating Systems ";
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const char* message2 = "Is Fun!";
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const char* msg_end = "\n";
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int shm_fd; // file descriptor, from shm_open()
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char* shm_base; // base address, from mmap()
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char* ptr; // shm_base is fixed, ptr is movable
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/* create the shared memory segment as if it was a file */
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shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666);
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if (shm_fd == -1)
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{
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printf("prod: Shared memory failed: %s\n", strerror(errno));
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exit(1);
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}
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/* configure the size of the shared memory segment */
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ftruncate(shm_fd, SIZE);
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/* map the shared memory segment to the address space of the process */
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shm_base = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
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if (shm_base == MAP_FAILED)
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{
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printf("prod: Map failed: %s\n", strerror(errno));
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// close and shm_unlink?
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exit(1);
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}
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/**
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* Write to the mapped shared memory region.
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*
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* We increment the value of ptr after each write, but we
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* are ignoring the possibility that sprintf() fails.
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*/
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display("prod", shm_base, 64);
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ptr = shm_base;
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ptr += sprintf(ptr, "%s", message0);
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ptr += sprintf(ptr, "%s", message1);
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ptr += sprintf(ptr, "%s", message2);
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ptr += sprintf(ptr, "%s", msg_end);
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display("prod", shm_base, 64);
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/* remove the mapped memory segment from the address space of the process */
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if (munmap(shm_base, SIZE) == -1)
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{
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printf("prod: Unmap failed: %s\n", strerror(errno));
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exit(1);
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}
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/* close the shared memory segment as if it was a file */
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if (close(shm_fd) == -1)
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{
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printf("prod: Close failed: %s\n", strerror(errno));
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exit(1);
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}
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return 0;
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}
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void display(char* prog, char* bytes, int n)
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{
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printf("display: %s\n", prog);
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for (int i = 0; i < n; i++)
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{
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printf("%02x%c", bytes[i], ((i+1)%16) ? ' ' : '\n');
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}
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printf("\n");
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}
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