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authorJustus Winter <4winter@informatik.uni-hamburg.de>2013-11-22 16:03:52 +0100
committerJustus Winter <4winter@informatik.uni-hamburg.de>2014-10-01 09:03:52 +0200
commit6b0ceb8aec7dc2d607523d7aadc2fec237ce2ca8 (patch)
treebfeb64fc252413033ddb7c08041bd876e5d48fb3 /doc
parenta8d611bdbf48906010c6cde67eb6ff720e715cf0 (diff)
ipc: provide the protected payload in ipc_kmsg_copyout_header
* ipc/ipc_kmsg.c (ipc_kmsg_copyout_header): If a protected payload is set for the destination port, provide it in msgh_protected_payload. * ipc/mach_msg.c (mach_msg_trap): Likewise in the fast paths. * doc/mach.texi (Message Receive): Document message semantics with protected payloads.
Diffstat (limited to 'doc')
-rw-r--r--doc/mach.texi19
1 files changed, 19 insertions, 0 deletions
diff --git a/doc/mach.texi b/doc/mach.texi
index b187888..c57e607 100644
--- a/doc/mach.texi
+++ b/doc/mach.texi
@@ -1949,6 +1949,25 @@ loses the receive right after the message was dequeued from it, then
right still exists, but isn't held by the caller, then
@code{msgh_local_port} specifies @code{MACH_PORT_NULL}.
+Servers usually associate some state with a receive right. To that
+end, they might use a hash table to look up the state for the port a
+message was sent to. To optimize this, a task may associate an opaque
+@var{payload} with a receive right using the
+@code{mach_port_set_protected_payload} function. Once this is done,
+the kernel will set the @code{msgh_protected_payload} field to
+@var{payload} when delivering a message to this right and indicate
+this by setting the local part of @code{msgh_bits} to
+@code{MACH_MSG_TYPE_PROTECTED_PAYLOAD}.
+
+The support for protected payloads was added to GNU Mach. To preserve
+binary compatibility, the @code{msgh_local_port} and
+@code{msgh_local_port} share the same location. This makes it
+possible to add the payload information without increasing the size of
+@code{mach_msg_header_t}. This is an implementation detail. Which
+field is valid is determined by the local part of the
+@code{msgh_bits}. Existing software is not affected. When a receive
+right is transferred to another task, its payload is cleared.
+
Received messages are stamped with a sequence number, taken from the
port from which the message was received. (Messages received from a
port set are stamped with a sequence number from the appropriate member