From a93b981fcb25ea049cec1bf4dff3e99c707275a7 Mon Sep 17 00:00:00 2001 From: Justus Winter <4winter@informatik.uni-hamburg.de> Date: Fri, 20 Jun 2014 13:04:25 +0200 Subject: add mach5 proposal --- microkernel/mach/gnumach/projects.mdwn | 2 + microkernel/mach/gnumach/projects/mach_5.mdwn | 75 +++++++++++++++++++++++++++ 2 files changed, 77 insertions(+) create mode 100644 microkernel/mach/gnumach/projects/mach_5.mdwn (limited to 'microkernel') diff --git a/microkernel/mach/gnumach/projects.mdwn b/microkernel/mach/gnumach/projects.mdwn index f4ef192a..62903fbe 100644 --- a/microkernel/mach/gnumach/projects.mdwn +++ b/microkernel/mach/gnumach/projects.mdwn @@ -35,6 +35,8 @@ so that no duplicate efforts end up. * [[Open Issues|tag/open_issue_gnumach]] + * [[Mach_5]] + * Update the core architecture and drivers * Check what NetBSD, FreeBSD and Linux do with their host specific code diff --git a/microkernel/mach/gnumach/projects/mach_5.mdwn b/microkernel/mach/gnumach/projects/mach_5.mdwn new file mode 100644 index 00000000..4f43a879 --- /dev/null +++ b/microkernel/mach/gnumach/projects/mach_5.mdwn @@ -0,0 +1,75 @@ +[[!meta copyright="Copyright © 2014 +Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_gnumach]] + +# The Mach5 proposal + +The Mach IPC mechanism is known to have deficiencies. Some of these +could be addressed with a new message ABI. A transition to 64-bit +architectures requires a new ABI definition anyway, so while we are at +it, we could straighten out some of these problems. + +This page is a place to keep track of such changes. + +## Protected payloads + +Protected payloads are a way of optimizing the receiver object lookup +in servers. A server may associate a payload with a receive right, +and any incoming message is tagged with it. The payload is an +pointer-wide unsigned integer, so the address of the associated server +side state can be used as payload. This removes the need for a hash +table lookup. + +### Required change to the message format + +Add a new field for the payload to the message header. + +### Implementation within the bounds of the Mach4 message format + +The payload can be provided in the same location as the local port +using an union. The kernel indicates this using a distinct message +type. MIG-generated code will detect this, and do the receiver lookup +using a specialized translation function. + +An almost complete prototype is available. + +* +* + +## Type descriptor rework + +A Mach4 message body contains pairs of type descriptors and values. +Each type descriptor describes the kind and amount of data that +immediately follows in the message stream. As the kernel has to +rewrite rights and pointers to out-of-band memory, it has to parse the +message. As type information and values are interleaved, it has to +iterate over the whole message. + +Furthermore, there are two kinds of type descriptors, mach_msg_type_t +and mach_msg_type_long_t. The reason for this is that the amount of +data that can be described using mach_msg_type_t is just 131072 byte. +This is because msgt_size is an 8-bit value describing the size of one +element in bits, and msgt_number is an 12-bit value describing the +number of items. + +### Required change to the message format + +Group the type descriptors together at the beginning of the message to +provide an index into the data. Provide the element size in multiple +of the native word size avoiding the need for long type descriptors. + +### Implementation within the bounds of the Mach4 message format + +The Mach4 type descriptor contains one unused bit. This bit can be +used to indicate that this message uses a Mach5 style index. MIG can +be modified to handle both cases for a smooth transition to the new +ABI. -- cgit v1.2.3