libuuid: add note about RFC4122 UUID layout

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/libuuid/src/uuidP.h b/libuuid/src/uuidP.h
index 86a5e266f..78183ded7 100644
--- a/libuuid/src/uuidP.h
+++ b/libuuid/src/uuidP.h
@@ -45,6 +45,35 @@
 #define TIME_OFFSET_HIGH 0x01B21DD2
 #define TIME_OFFSET_LOW  0x13814000
 
+/*
+ * Note that RFC4122 defines UUID in more details:
+ *
+ *     Field               Data Type     Octet  Note
+ * -------------------------------------------------
+ *  time_low               unsigned 32   0-3    The low field of the
+ *                         bit integer          timestamp
+ *
+ *  time_mid               unsigned 16   4-5    The middle field of the
+ *                         bit integer          timestamp
+ *
+ *  time_hi_and_version    unsigned 16   6-7    The high field of the
+ *                         bit integer          timestamp multiplexed
+ *                                              with the version number
+ *
+ *  clock_seq_hi_and_rese  unsigned 8    8      The high field of the
+ *  rved                   bit integer          clock sequence
+ *                                              multiplexed with the
+ *                                              variant
+ *
+ *  clock_seq_low          unsigned 8    9      The low field of the
+ *                         bit integer          clock sequence
+ *
+ *  node                   unsigned 48   10-15  The spatially unique
+ *                         bit integer          node identifier
+ *
+ * We have clock_seq_hi_and_reserved (8bit) and clock_seq_low (8bit)
+ * merged into clock_seq (16bit).
+ */
 struct uuid {
 	uint32_t	time_low;
 	uint16_t	time_mid;