Measuring Holes

This appendix contains the interesting part of the program used to measure the potential for holes in a filesystem. The source distribution of the book contains the full source code (sag/measure-holes/measure-holes.c).

int process(FILE *f, char *filename) {
static char *buf = NULL;
static long prev_block_size = -1;
long zeroes;
char *p;

if (buf == NULL || prev_block_size != block_size) {
free(buf);
buf = xmalloc(block_size + 1);
buf[block_size] = 1;
prev_block_size = block_size;
}
zeroes = 0;
while (fread(buf, block_size, 1, f) == 1) {
for (p = buf; *p == '\0'; )
++p;
if (p == buf+block_size)
zeroes += block_size;
}
if (zeroes > 0)
printf("%ld %s\n", zeroes, filename);
if (ferror(f)) {
errormsg(0, -1, "read failed for `%s'", filename);
return -1;
}
return 0;
}