Re: [PATCH] cld: use XDR for all messages

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On 01/10/2010 10:00 AM, Colin McCabe wrote:
This patch moves CLD from using manual data serialization to using XDR (via
rpcgen). Both the packet header and the message body are now serialized and
deserialized using XDR. This makes it easy to have a variable-length packet
header, as well as a variable-length message body.

Message definitions are now in cld_msg.x. Helper functions for using messages
are in cld_fmt.c. The new client and server-side functions for sending
messages don't require the caller to precompute the size of the message.
Instead, you simply tell it what type of message you have, and give it the
data. It handles determining message size and encoding.

The only fields that I did not choose to deal with using XDR are the packet
sequence ID and the packet SHA checksum. The seqid would have been
inconvenient and inefficient to store in the XDR header, because we have to
check a lot of packets' seqids against the ACKs we receive very frequently.
The SHA checksum can't be computed until the rest of the packet has been
serialized, which is counter to the way XDR works (it is a single-pass
serialization system.) So these fields are in the packet footer, which comes
at the end of every packet.

This patch introduces a minor libcldc API change in struct cldc_call_opts.

Signed-off-by: Colin McCabe<cmccabe@xxxxxxxxxxxxxx>
---
  .gitignore             |    4 +
  include/Makefile.am    |    2 +-
  include/cld_common.h   |   10 +
  include/cld_fmt.h      |   78 ++++
  include/cld_msg.h      |  252 -------------
  include/cldc.h         |   37 +-
  lib/Makefile.am        |   14 +-
  lib/cld_fmt.c          |  189 ++++++++++
  lib/cld_msg_rpc.x      |  212 +++++++++++
  lib/cldc.c             |  960 +++++++++++++++++++++---------------------------
  lib/common.c           |    6 +-
  server/Makefile.am     |    9 +-
  server/cld.h           |   97 ++++--
  server/cldb.h          |    2 +-
  server/msg.c           |  304 ++++++----------
  server/server.c        |  743 ++++++++++++++++++++-----------------
  server/session.c       |  396 ++++++++++-----------
  test/load-file-event.c |   14 +-
  test/save-file-event.c |    2 -
  tools/cldcli.c         |   22 +-
  20 files changed, 1744 insertions(+), 1609 deletions(-)
  create mode 100644 include/cld_fmt.h
  delete mode 100644 include/cld_msg.h
  create mode 100644 lib/cld_fmt.c
  create mode 100644 lib/cld_msg_rpc.x

Fantastic! This will take a day or two to review, so please be a little bit patient, waiting for the patch to be applied.

At first glance, it looks pretty good.

Thanks, this will really help with future protocol changes, most notably (a) fleshing out multi-master support and (b) introducing cache coherency.

	Jeff




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