[ros-diffs] [ion] 17421: Add beginning of lpc docs

Add beginning of lpc docs
Added: trunk/reactos/media/doc/LPC.txt
  _____  

Added: trunk/reactos/media/doc/LPC.txt
--- trunk/reactos/media/doc/LPC.txt	2005-08-17 07:06:59 UTC (rev
17420)
+++ trunk/reactos/media/doc/LPC.txt	2005-08-17 07:07:43 UTC (rev
17421)
@@ -0,0 +1,53 @@

+==============================================================
+=                                                            =
+=               NOTES FROM THE UNDERGROUND                   =
+=                                                            =
+==============================================================
+Below are some of Alex's notes on the mysterious LPC Subsystem
+
+=========================
+1. Sizes, sizes, sizes...
+=========================
+
+There are four imporant LPC Sizes to keep in mind. Try to understand
them:
+
+/* 
+ * This determines the absolute maximum message size (0x100 bytes). For
+ * larger values, use a section-backed message.
+ */
+#define PORT_MAXIMUM_MESSAGE_LENGTH 256
+
+/*
+ * This determines the maximum length of an LPC request. It is the
largest
+ * amount of bytes that an LPC request can take. To calculate this,
assume
+ * that this is a CONNECTION_REQUEST message, which includes the
additionnal
+ * LPCP_CONNECTION_MESSAGE structure as well. Therefore, we add the
kernel LPC,
+ * header, the maximum port size and the size of the connection request
+ * structure. This gives a value of 0x15C. However, one must note that
NT
+ * allocates the Lookaside List using a 16-byte aligned value, making
this
+ * number 0x160.
+ */
+#define LPCP_MAX_MESSAGE_SIZE   ROUND_UP(PORT_MAXIMUM_MESSAGE_LENGTH +
\
+                                         sizeof(LPCP_MESSAGE) + \
+
sizeof(LPCP_CONNECTION_MESSAGE), 16)
+
+/*
+ * Now, for an actual LPC Request size, we remove the kernel LPC
header, which
+ * yields the size of the actual LPC Data that follows the Header,
making this
+ * number 0x148.
+ */
+#define LPC_MAX_MESSAGE_LENGTH (LPCP_MAX_MESSAGE_SIZE - \
+                                FIELD_OFFSET(LPCP_MESSAGE, Request))
+
+/*
+ * Finally, we'll calculate the maximum size of the Connection Info,
giving us
+ * 0x104
+ */
+#define LPC_MAX_DATA_LENGTH     (LPC_MAX_MESSAGE_LENGTH - \
+                                 sizeof(PORT_MESSAGE) - \
+                                 sizeof(LPCP_CONNECTION_MESSAGE))
+
+==========================
+2. Structures
+==========================
+SOON. TODO.
\ No newline at end of file