[KERNEL32] Minor enhancements for CreateRemoteThread(). (#804)
[reactos.git] / media / doc / LPC.txt
1 ==============================================================
2 = =
3 = NOTES FROM THE UNDERGROUND =
4 = =
5 ==============================================================
6 Below are some of Alex's notes on the mysterious LPC Subsystem
7
8 =========================
9 1. Sizes, sizes, sizes...
10 =========================
11
12 There are four imporant LPC Sizes to keep in mind. Try to understand them:
13
14 /*
15 * This determines the absolute maximum message size (0x100 bytes). For
16 * larger values, use a section-backed message.
17 */
18 #define PORT_MAXIMUM_MESSAGE_LENGTH 256
19
20 /*
21 * This determines the maximum length of an LPC request. It is the largest
22 * amount of bytes that an LPC request can take. To calculate this, assume
23 * that this is a CONNECTION_REQUEST message, which includes the additionnal
24 * LPCP_CONNECTION_MESSAGE structure as well. Therefore, we add the kernel LPC,
25 * header, the maximum port size and the size of the connection request
26 * structure. This gives a value of 0x15C. However, one must note that NT
27 * allocates the Lookaside List using a 16-byte aligned value, making this
28 * number 0x160.
29 */
30 #define LPCP_MAX_MESSAGE_SIZE ROUND_UP(PORT_MAXIMUM_MESSAGE_LENGTH + \
31 sizeof(LPCP_MESSAGE) + \
32 sizeof(LPCP_CONNECTION_MESSAGE), 16)
33
34 /*
35 * Now, for an actual LPC Request size, we remove the kernel LPC header, which
36 * yields the size of the actual LPC Data that follows the Header, making this
37 * number 0x148.
38 */
39 #define LPC_MAX_MESSAGE_LENGTH (LPCP_MAX_MESSAGE_SIZE - \
40 FIELD_OFFSET(LPCP_MESSAGE, Request))
41
42 /*
43 * Finally, we'll calculate the maximum size of the Connection Info, giving us
44 * 0x104
45 */
46 #define LPC_MAX_DATA_LENGTH (LPC_MAX_MESSAGE_LENGTH - \
47 sizeof(PORT_MESSAGE) - \
48 sizeof(LPCP_CONNECTION_MESSAGE))
49
50 ==========================
51 2. Structures
52 ==========================
53 SOON. TODO.