Changes

When the kernel processes X descriptors, it must determine where to copy the data to. If the destination used C descriptors with flags >= 3, each X descriptor from the source is matched to a C descriptor in the destination by the X descriptor's index field. If the destination used a "single" C descriptor, the data from all the X descriptors is copied into the same buffer specified by the destination's C descriptor (causing error 0xce01 if there is not enough space) and the X descriptor index is ignored. The kernel then modifies the addresses in the X descriptors to indicate where the data was copied to in the destination.

When the kernel processes X descriptors, it must determine where to copy the data to. If the destination used C descriptors with flags >= 3, each X descriptor from the source is matched to a C descriptor in the destination by the X descriptor's index field. If the destination used a "single" C descriptor, the data from all the X descriptors is copied into the same buffer specified by the destination's C descriptor (causing error 0xce01 if there is not enough space) and the X descriptor index is ignored. The kernel then modifies the addresses in the X descriptors to indicate where the data was copied to in the destination.

Before receiving a request, if the IPC server is expecting X descriptors, it prepares a message with a "single" C descriptor (flags=2) in its message buffer before calling svcReplyAndReceive so that X descriptors from the client have a place to copy their data to.  The usage of the flag-2 C descriptor allows the server to receive an arbitrary number of X descriptors, since they're all packed into the same buffer. If the server had used flag-3+ C descriptors, it would be limited in how many X descriptors it could receive since the X descriptors would have to be matched to distinct C descriptors. The buffer that the server's C descriptor points to is called the **pointer buffer**.

Before receiving a request, if the IPC server is expecting X descriptors, it prepares a message with a "single" C descriptor (flags=2) in its message buffer before calling svcReplyAndReceive so that X descriptors from the client have a place to copy their data to.  The usage of the flag-2 C descriptor allows the server to receive an arbitrary number of X descriptors, since they're all packed into the same buffer. If the server had used flag-3+ C descriptors, it would be limited in how many X descriptors it could receive since the X descriptors would have to be matched to distinct C descriptors. The buffer that the server's C descriptor points to is called the '''pointer buffer'''.

When the client sends X descriptors, data is copied into the server's pointer buffer. When the client sends C descriptors, no data is copied automatically. The server needs to use X descriptors to copy the data back to the client's C descriptors (using the index field to match X descriptors in the response back to the correct C descriptors).

When the client sends X descriptors, data is copied into the server's pointer buffer. When the client sends C descriptors, no data is copied automatically. The server needs to use X descriptors to copy the data back to the client's C descriptors (using the index field to match X descriptors in the response back to the correct C descriptors).