71 lines
1.8 KiB
C
71 lines
1.8 KiB
C
// Persistent stack example of how mmap() naturally creates a software abstraction of persistent memory.
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// Author: Terence Kelly <tpklly@acm.org>
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// Note: Use 'dd' to make the initial (empty) image, e.g.,
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// dd if=/dev/zero of=ps.img bs=32 count=1
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// makes a 32-byte empty file (the first integer being the size of the stack,
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// the remaining integers being values)
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#include <assert.h>
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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 <string.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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int open_or_die(const char *path, int oflag) {
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int fd = open(path, oflag);
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assert(fd > 0);
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return fd;
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}
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int fstat_or_die(int fildes, struct stat *buf) {
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int rc = fstat(fildes, buf);
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assert(rc == 0);
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return rc;
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}
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void *mmap_or_die(void *addr, size_t len, int prot, int flags, int fd, off_t offset) {
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void *p = mmap(addr, len, prot, flags, fd, offset);
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assert(p != MAP_FAILED);
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return p;
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}
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typedef struct {
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size_t n;
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int stack[]; // zero-length per C99
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} pstack_t;
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int main(int argc, char *argv[]) {
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int fd, rc;
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struct stat s;
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size_t file_size;
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pstack_t *p;
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fd = open_or_die("ps.img", O_RDWR);
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rc = fstat_or_die(fd, &s);
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file_size = (size_t) s.st_size;
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assert(file_size % sizeof(int) == 0);
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p = mmap_or_die(NULL, file_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
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for (int i = 1; i < argc; i++)
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if (strcmp(argv[i], "pop") == 0) {
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if (p->n > 0) // stack not empty
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printf("%d\n", p->stack[--p->n]);
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else
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printf("stack empty\n");
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} else
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if (sizeof(pstack_t) + p->n * sizeof(int) < file_size) // stack not full
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p->stack[p->n++] = atoi(argv[i]);
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else
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printf("stack full: %d not added\n", atoi(argv[i]));
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close(fd);
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return 0;
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}
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