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/* seek.c - use lseek() to find holes in a file
*
* Author: Niels de Vos <ndevos@redhat.com>
*/
/* needed for SEEK_HOLE/SEEK_DATA */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main (int argc, char **argv)
{
int ret = EXIT_SUCCESS;
int fd = -1;
char *filename = NULL;
struct stat st = { 0, };
off_t hole_start = 0;
off_t hole_end = 0;
if (argc != 2) {
fprintf (stderr, "Invalid argument, use %s <file>\n", argv[0]);
return EXIT_FAILURE;
}
filename = argv[1];
fd = open (filename, O_RDONLY);
if (fd <= 0) {
perror ("open");
return EXIT_FAILURE;
}
if (fstat (fd, &st)) {
perror ("fstat");
return EXIT_FAILURE;
}
while (hole_end < st.st_size) {
hole_start = lseek (fd, hole_end, SEEK_HOLE);
if (hole_start == -1 && errno == ENXIO) {
/* no more holes */
break;
} else if (hole_start == -1 && errno == ENOTSUP) {
/* SEEK_HOLE is not supported */
perror ("lseek(SEEK_HOLE)");
ret = EXIT_FAILURE;
break;
} else if (hole_start == -1) {
perror ("no more holes");
break;
}
hole_end = lseek (fd, hole_start, SEEK_DATA);
if (hole_end == -1 && errno == ENXIO) {
/* no more data */
break;
} else if (hole_end == -1 && errno == ENOTSUP) {
/* SEEK_DATA is not supported */
perror ("lseek(SEEK_DATA)");
ret = EXIT_FAILURE;
break;
}
printf ("HOLE found: %ld - %ld%s\n", hole_start, hole_end,
(hole_end == st.st_size) ? " (EOF)" : "");
}
close (fd);
return ret;
}
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