zdtm: lib: add {read,write}_data helpers

Some tests expect that all the data will be handled in a single invocation
of read/write system call. But it possible to have short read/write on a
loaded system and this is not an error.
Add helper functions that will reliably read/write the entire buffer.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/lib/streamutil.c

@@ -40,3 +40,36 @@ int pipe_in2out(int infd, int outfd, uint8_t *buffer, int length)
 		}
 	}
 }
+
+int read_data(int fd, unsigned char *buf, int size)
+{
+	int cur = 0;
+	int ret;
+	while (cur != size) {
+		ret = read(fd, buf + cur, size - cur);
+		if (ret <= 0) {
+			pr_perror("read(%d) = %d", size - cur, ret);
+			return -1;
+		}
+		cur += ret;
+	}
+
+	return 0;
+}
+
+int write_data(int fd, const unsigned char *buf, int size)
+{
+	int cur = 0;
+	int ret;
+
+	while (cur != size) {
+		ret = write(fd, buf + cur, size - cur);
+		if (ret <= 0) {
+			pr_perror("write(%d) = %d", size - cur, ret);
+			return -1;
+		}
+		cur += ret;
+	}
+
+	return 0;
+}

test/zdtm/lib/zdtmtst.h

@@ -55,6 +55,8 @@ extern int datasum(const uint8_t *buffer, unsigned length, uint32_t *crc);
 /* streaming helpers */
 extern int set_nonblock(int fd, int on);
 extern int pipe_in2out(int infd, int outfd, uint8_t *buffer, int length);
+extern int read_data(int fd, unsigned char *buf, int len);
+extern int write_data(int fd, const unsigned char *buf, int len);
 
 /* command line args */
 struct long_opt {