77 lines
1.7 KiB
C
77 lines
1.7 KiB
C
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <string.h>
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#define handle_error(msg) \
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do { perror(msg); exit(EXIT_FAILURE); } while (0)
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int main(int argc, char *argv[])
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{
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int fd;
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char *addr;
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off_t offset, pa_offset;
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size_t length;
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ssize_t s;
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struct stat sb;
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if (argc < 3 || argc > 4) {
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fprintf(stderr, "%s file offset [length]\n", argv[0]);
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exit(EXIT_FAILURE);
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}
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fd = open(argv[1], O_RDWR);
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if (fd == -1)
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handle_error("open");
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if (fstat(fd, &sb) == -1) /* To obtain file size */
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handle_error("fstat");
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offset = atoi(argv[2]);
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pa_offset = offset & ~(sysconf(_SC_PAGE_SIZE) - 1);
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/* offset for mmap() must be page aligned */
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if (offset >= sb.st_size) {
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fprintf(stderr, "offset is past end of file\n");
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exit(EXIT_FAILURE);
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}
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if (argc == 4) {
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length = atoi(argv[3]);
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if (offset + length > sb.st_size)
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length = sb.st_size - offset;
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/* Can't display bytes past end of file */
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} else { /* No length arg ==> display to end of file */
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length = sb.st_size - offset;
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}
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addr = mmap(NULL, length + offset - pa_offset, PROT_READ | PROT_WRITE,
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MAP_SHARED, fd, pa_offset);
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if (addr == MAP_FAILED)
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handle_error("mmap");
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printf("address is 0x%x\n", (unsigned long)addr);
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//write(fd, "", 1);
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memcpy(addr, "haowenchao", 11);
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msync(addr, sb.st_size, MS_SYNC);
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s = write(STDOUT_FILENO, addr + offset - pa_offset, length);
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if (s != length) {
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if (s == -1)
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handle_error("write");
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fprintf(stderr, "partial write");
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exit(EXIT_FAILURE);
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}
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munmap(addr, length + offset - pa_offset);
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close(fd);
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exit(EXIT_SUCCESS);
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}
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