I just check in a short doc explaining some tricks to use when debugging Vino.
I got a bit side tracked explaining how you can figure out what messages
are being sent back and forth to the X server, just by looking at the
read()s and write()s in the strace. A snippet:
[markmc@blaa ~]$ grep -rn X_QueryExtension /usr/include/X11/Xproto.h
2091:#define X_QueryExtension 98
That's 0x62 in hex. So, we're looking for a write to the X
connection (file descriptor 3) with 0x62 as the first byte. What do ya
know:
1117012824.950683 writev(3, [{"\x62\x01\x04\x00\x06\x00\x01\x00", 8}, {"DAMAGE", 6}, {"\x00\x00", 2}], 3) = 16
1117012824.950939 read(3, "\x01\x00\x52\x00\x00\x00\x00\x00\x01\x9d\x75\xba\x00\x00"..., 32) = 32
It's pretty clear that its QueryExtension for DAMAGE. Now, lets
figure out the event base from the reply. The format for the reply is:
typedef struct {
BYTE type; /* X_Reply */
BYTE pad1;
CARD16 sequenceNumber B16;
CARD32 length B32; /* 0 */
BOOL present;
CARD8 major_opcode;
CARD8 first_event;
...
} xQueryExtensionReply;
first_event is 11 bytes in. Looking at the read, that's 0x75. The
value of XDamageNotify is zero, so we can be 100% sure that all those
events after our NoExpose events are XDamageNotify events.
