Fix ztest vdev file paths.

Currently, in several instances (but not all), ztest generates vdev
file paths using a statement similar to this:

    snprintf(path, sizeof (path), ztest_dev_template, ...);

This worked fine until 40b84e7, which
changed path to be a pointer to the heap instead of an array allocated
on the stack. Before this change, sizeof(path) would return the size of
the array; now, it returns the size of the pointer instead.

As a result, the aforementioned sprintf statement uses the wrong size
and truncates the vdev file path to the first 4 or 8 bytes (depending
on the architecture). Typically, with default settings, the file path
will become "/tmp/zt" instead of "/test/ztest.XXX".

This issue only exists in ztest_vdev_attach_detach() and
ztest_fault_inject(), which explains why ztest doesn't fail right away.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #989

cmd/ztest/ztest.c

@@ -2567,7 +2567,7 @@ ztest_vdev_attach_detach(ztest_ds_t *zd, uint64_t id)
 		newvd_is_spare = B_TRUE;
 		(void) strcpy(newpath, newvd->vdev_path);
 	} else {
-		(void) snprintf(newpath, sizeof (newpath), ztest_dev_template,
+		(void) snprintf(newpath, MAXPATHLEN, ztest_dev_template,
 		    zopt_dir, zopt_pool, top * leaves + leaf);
 		if (ztest_random(2) == 0)
 			newpath[strlen(newpath) - 1] = 'b';
@@ -4633,9 +4633,9 @@ ztest_fault_inject(ztest_ds_t *zd, uint64_t id)
 		 * write failures and random online/offline activity on leaf 0,
 		 * and we'll write random garbage to the randomly chosen leaf.
 		 */
-		(void) snprintf(path0, sizeof (path0), ztest_dev_template,
+		(void) snprintf(path0, MAXPATHLEN, ztest_dev_template,
 		    zopt_dir, zopt_pool, top * leaves + zs->zs_splits);
-		(void) snprintf(pathrand, sizeof (pathrand), ztest_dev_template,
+		(void) snprintf(pathrand, MAXPATHLEN, ztest_dev_template,
 		    zopt_dir, zopt_pool, top * leaves + leaf);
 
 		vd0 = vdev_lookup_by_path(spa->spa_root_vdev, path0);
@@ -4999,7 +4999,7 @@ ztest_run_zdb(char *pool)
 
 	fp = popen(zdb, "r");
 
-	while (fgets(zbuf, sizeof (zbuf), fp) != NULL)
+	while (fgets(zbuf, 1024, fp) != NULL)
 		if (zopt_verbose >= 3)
 			(void) printf("%s", zbuf);