um: Fix WRITE_ZEROES in the UBD Driver

Call to fallocate with FALLOC_FL_PUNCH_HOLE on a device backed by a sparse
file can end up by missing data, zeroes data range, if the underlying file
is used with a tool like bmaptool which will referenced only used spaces.
Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/ubd_kern.c

@@ -1526,13 +1526,19 @@ static void do_io(struct io_thread_req *req, struct io_desc *desc)
 			}
 			break;
 		case REQ_OP_DISCARD:
-		case REQ_OP_WRITE_ZEROES:
 			n = os_falloc_punch(req->fds[bit], off, len);
 			if (n) {
 				req->error = map_error(-n);
 				return;
 			}
 			break;
+		case REQ_OP_WRITE_ZEROES:
+			n = os_falloc_zeroes(req->fds[bit], off, len);
+			if (n) {
+				req->error = map_error(-n);
+				return;
+			}
+			break;
 		default:
 			WARN_ON_ONCE(1);
 			req->error = BLK_STS_NOTSUPP;

arch/um/include/shared/os.h

@@ -168,6 +168,7 @@ extern unsigned os_major(unsigned long long dev);
 extern unsigned os_minor(unsigned long long dev);
 extern unsigned long long os_makedev(unsigned major, unsigned minor);
 extern int os_falloc_punch(int fd, unsigned long long offset, int count);
+extern int os_falloc_zeroes(int fd, unsigned long long offset, int count);
 extern int os_eventfd(unsigned int initval, int flags);
 extern int os_sendmsg_fds(int fd, const void *buf, unsigned int len,
 			  const int *fds, unsigned int fds_num);

arch/um/os-Linux/file.c

@@ -625,6 +625,15 @@ int os_falloc_punch(int fd, unsigned long long offset, int len)
 	return n;
 }
 
+int os_falloc_zeroes(int fd, unsigned long long offset, int len)
+{
+	int n = fallocate(fd, FALLOC_FL_ZERO_RANGE|FALLOC_FL_KEEP_SIZE, offset, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
 int os_eventfd(unsigned int initval, int flags)
 {
 	int fd = eventfd(initval, flags);