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Add beginning of lpc docs

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Alex Ionescu 2005-08-17 07:07:43 +00:00
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reactos/media/doc/LPC.txt Normal file
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==============================================================
= =
= 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.