macro: add INTTYPE_TO_STRLEN()

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/macro.h b/src/lxc/macro.h
index 17cf0eb195400033bef56288242586b8a9a6b36b..8e7ef12c6d0491915422e92f3b748800a9f3e3a6 100644 (file)
--- a/src/lxc/macro.h
+++ b/src/lxc/macro.h
@@ -104,9 +104,24 @@
 #define OVERLAY_SUPER_MAGIC 0x794c7630
 #endif
 
+/* Calculate the number of chars needed to represent a given integer as a C
+ * string. Include room for '-' to indicate negative numbers and the \0 byte.
+ * This is based on systemd.
+ */
+#define INTTYPE_TO_STRLEN(type)                   \
+       (2 + (sizeof(type) <= 1                   \
+                 ? 3                             \
+                 : sizeof(type) <= 2             \
+                       ? 5                       \
+                       : sizeof(type) <= 4       \
+                             ? 10                \
+                             : sizeof(type) <= 8 \
+                                   ? 20          \
+                                   : sizeof(int[-2 * (sizeof(type) > 8)])))
+
 /* Useful macros */
 /* Maximum number for 64 bit integer is a string with 21 digits: 2^64 - 1 = 21 */
-#define LXC_NUMSTRLEN64 21
+#define LXC_NUMSTRLEN64 INTTYPE_TO_STRLEN(int64_t)
 #define LXC_LINELEN 4096
 #define LXC_IDMAPLEN 4096
 #define LXC_MAX_BUFFER 4096