tools/testing/selftests/vm/gup_benchmark.c: allow user specified file

Allow a user to specify a file to map by adding a new option, '-f',
providing a means to test various file backings.

If not specified, the benchmark will use a private mapping of /dev/zero,
which produces an anonymous mapping as before.

[akpm@linux-foundation.org: avoid using comma operator]
Link: http://lkml.kernel.org/r/20181010195605.10689-4-keith.busch@intel.com
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/gup_benchmark.c

@@ -31,11 +31,12 @@ int main(int argc, char **argv)
 {
 	struct gup_benchmark gup;
 	unsigned long size = 128 * MB;
-	int i, fd, opt, nr_pages = 1, thp = -1, repeats = 1, write = 0;
+	int i, fd, filed, opt, nr_pages = 1, thp = -1, repeats = 1, write = 0;
 	int cmd = GUP_FAST_BENCHMARK;
+	char *file = "/dev/zero";
 	char *p;
 
-	while ((opt = getopt(argc, argv, "m:r:n:tTLU")) != -1) {
+	while ((opt = getopt(argc, argv, "m:r:n:f:tTLU")) != -1) {
 		switch (opt) {
 		case 'm':
 			size = atoi(optarg) * MB;
@@ -61,20 +62,28 @@ int main(int argc, char **argv)
 		case 'w':
 			write = 1;
 			break;
+		case 'f':
+			file = optarg;
+			break;
 		default:
 			return -1;
 		}
 	}
 
+	filed = open(file, O_RDWR|O_CREAT);
+	if (filed < 0) {
+		perror("open");
+		exit(filed);
+	}
+
 	gup.nr_pages_per_call = nr_pages;
 	gup.flags = write;
 
 	fd = open("/sys/kernel/debug/gup_benchmark", O_RDWR);
 	if (fd == -1)
 		perror("open"), exit(1);
 
-	p = mmap(NULL, size, PROT_READ | PROT_WRITE,
-			MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	p = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, filed, 0);
 	if (p == MAP_FAILED)
 		perror("mmap"), exit(1);
 	gup.addr = (unsigned long)p;