img: Move images IO helpers into .c file

This is to simplify the change from int fd to more
generic image class data-type.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>

image.c

@@ -315,3 +315,91 @@ int open_pages_image(unsigned long flags, int pm_fd)
 {
 	return open_pages_image_at(get_service_fd(IMG_FD_OFF), flags, pm_fd);
 }
+
+/*
+ * Write buffer @ptr of @size bytes into @fd file
+ * Returns
+ *	0  on success
+ *	-1 on error (error message is printed)
+ */
+int write_img_buf(int fd, const void *ptr, int size)
+{
+	int ret;
+	ret = write(fd, ptr, size);
+	if (ret == size)
+		return 0;
+
+	if (ret < 0)
+		pr_perror("Can't write img file");
+	else
+		pr_err("Img trimmed %d/%d\n", ret, size);
+	return -1;
+}
+
+/*
+ * Read buffer @ptr of @size bytes from @fd file
+ * Returns
+ *	1  on success
+ *	0  on EOF (silently)
+ *	-1 on error (error message is printed)
+ */
+int read_img_buf_eof(int fd, void *ptr, int size)
+{
+	int ret;
+	ret = read(fd, ptr, size);
+	if (ret == size)
+		return 1;
+	if (ret == 0)
+		return 0;
+
+	if (ret < 0)
+		pr_perror("Can't read img file");
+	else
+		pr_err("Img trimmed %d/%d\n", ret, size);
+	return -1;
+}
+
+/*
+ * Read buffer @ptr of @size bytes from @fd file
+ * Returns
+ *	1  on success
+ *	-1 on error or EOF (error message is printed)
+ */
+int read_img_buf(int fd, void *ptr, int size)
+{
+	int ret;
+
+	ret = read_img_buf_eof(fd, ptr, size);
+	if (ret == 0) {
+		pr_err("Unexpected EOF\n");
+		ret = -1;
+	}
+
+	return ret;
+}
+
+/*
+ * read_img_str -- same as read_img_buf, but allocates memory for
+ * the buffer and puts the '\0' at the end
+ */
+
+int read_img_str(int fd, char **pstr, int size)
+{
+	int ret;
+	char *str;
+
+	str = xmalloc(size + 1);
+	if (!str)
+		return -1;
+
+	ret = read_img_buf(fd, str, size);
+	if (ret < 0) {
+		xfree(str);
+		return -1;
+	}
+
+	str[size] = '\0';
+	*pstr = str;
+	return 0;
+}
+