f3read, f3write: chdir(2) to source/target dir

This makes the dir non-umount-able for the program's lifetime.

f3read.c

@@ -434,6 +434,8 @@ int main(int argc, char **argv)
 	argp_parse(&argp, argc, argv, 0, NULL, &args);
 	print_header(stdout, "read");
 
+	adjust_dev_path(&args.dev_path);
+
 	files = ls_my_files(args.dev_path, args.start_at, args.end_at);
 
 	iterate_files(args.dev_path, files, args.start_at, args.end_at,

f3write.c

@@ -368,6 +368,8 @@ int main(int argc, char **argv)
 	argp_parse(&argp, argc, argv, 0, NULL, &args);
 	print_header(stdout, "write");
 
+	adjust_dev_path(&args.dev_path);
+
 	unlink_old_files(args.dev_path, args.start_at, args.end_at);
 
 	return fill_fs(args.dev_path, args.start_at, args.end_at,

utils.c

@@ -18,10 +18,20 @@
 #include <dirent.h>
 #include <errno.h>
 #include <err.h>
+#include <unistd.h>
 
 #include "version.h"
 #include "utils.h"
 
+void adjust_dev_path(const char **dev_path)
+{
+	if (chdir(*dev_path)) {
+		err(errno, "Can't change working directory to %s at %s()", *dev_path, __func__);
+	}
+
+	*dev_path = ".";
+}
+
 const char *adjust_unit(double *ptr_bytes)
 {
 	const char *units[] = { "Byte", "KB", "MB", "GB", "TB", "PB", "EB" };
@@ -216,8 +226,6 @@ int posix_fadvise(int fd, off_t offset, off_t len, int advice)
 
 #if (__APPLE__ && __MACH__) || defined(__OpenBSD__)
 
-#include <unistd.h> /* For usleep(). */
-
 void msleep(double wait_ms)
 {
 	assert(!usleep(wait_ms * 1000));

utils.h

@@ -9,6 +9,8 @@
 #define SECTOR_SIZE (512)
 #define GIGABYTES   (1024 * 1024 * 1024)
 
+void adjust_dev_path(const char **dev_path);
+
 const char *adjust_unit(double *ptr_bytes);
 
 /* Return true if @filename matches the regex /^[0-9]+\.h2w$/ */