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Commit c5774968 authored by Tim Wickberg's avatar Tim Wickberg
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Fix spelling mistakes in rpc.shtml and redo with Unix line endings.

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<!--#include virtual="header.txt"-->
<h1>Remote Procedure Call (RPC) Update Guide</h1>
<h2>Overview</h2>
<p>Slurm uses RPCs (Remote Procedure Calls) to communticate between
daemons and commands.
The format of many RPCs change between major and/or minor Slurm releases
(the release numbers are major.minor.micro and changes in the micro number
indicate bug fixes since the previous release, while changes in the
major or minor numbers indicate fundamental changes in logic).
The reason for format changes is typically new fields being added for new
Slurm capabilities.
Slurm communicatins support the most current release plus the two previous
release major and/or minor releases.
For example, Slurm version 15.08.x daemons can communicate with Slurm commands
from version 14.03.x, 14.11.x and 15.08.x.
The same is true for state save files.
Slurm can be upgraded through two major or minor releases without loss of data
since the older state files are still recognized.
Slurm commands initiated under one version of Slurm can also continue to
execute and communicate with the Slurm daemons through two release upgrades
of the daemons.
Upgrades beyond two releases will result in unrecognized state information,
but intermediate upgrades can be performed to reformat the state information
and prevent its loss.
As new versions of Slurm are relased, support for the oldest communication
protocols is removed from the code.</p>
<h2>Code Changes</h2>
<p>The code used for packing and unpacking RPCs can be mostly found in
<b>src/common</b>, although additional logic can also be found in each of
of the Slurm daemons (slurmctld, slurmd, and slurmdbd) plus some of the
plugins.</p>
<p>All RPCs and state save files contain Slurm version information.
This version information permits the server to recognize its format and
respond using a message format understood by the client.
When fields are added to or removed from existing RPCs, it is essential
that only the format of RPCs for the newest release of Slurm (which is still
under development) altered to avoid breaking pre-existing communication
protocols.
It may be necessary to add a new protocol version number to the code and
support for releases beyond two previous releases may be removed.
In the new code, copy the pack and unpack logic from the previous version of
the code and add new fields as needed.
Be sure to pack and unpack data in the identical order.
It is also important to keep in mind that when adding support for new fields
in an RPC protocol, that logic may need to be added to the older protocols
setting the new field values to a reasonable default value (e.g. NULL, 0).
For example, if a job is submitted using an old version of sbatch to a newer
slurmctld daemon, job specifications that are unknown to the old sbatch
should be set by the slurmctld daemon to reasonable values.
An example of the changes required are shown below.
In this trivial example, we want to add a new "max_nodes" filed to the
message for Slurm vestion 15.08.x.</p>
<pre>
/*
* Original code in Slurm v2.5.x
*/
if (protocol_version >= SLURM_14_11_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
} else if (protocol_version >= SLURM_14_03_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
} else if (protocol_version >= SLURM_13_08_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
} else {
error("pack_whatever_msg: protocol_version "
"%hu not supported", protocol_version);
}
</pre>
<pre>
/*
* New code in Slurm v15.08.x
*/
if (protocol_version >= SLURM_15_08_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
pack32(msg->max_nodes, buffer);
} else if (protocol_version >= SLURM_14_11_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
} else if (protocol_version >= SLURM_14_03_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
} else {
error("pack_whatever_msg: protocol_version "
"%hu not supported", protocol_version);
}
</pre>
<p style="text-align:center;">Last modified 15 April 2015</p>
<!--#include virtual="footer.txt"-->
<!--#include virtual="header.txt"-->
<h1>Remote Procedure Call (RPC) Update Guide</h1>
<h2>Overview</h2>
<p>Slurm uses RPCs (Remote Procedure Calls) to communicate between
daemons and commands.
The format of many RPCs change between major and/or minor Slurm releases
(the release numbers are major.minor.micro and changes in the micro number
indicate bug fixes since the previous release, while changes in the
major or minor numbers indicate fundamental changes in logic).
The reason for format changes is typically new fields being added for new
Slurm capabilities.
Slurm communications support the most current release plus the two previous
release major and/or minor releases.
For example, Slurm version 15.08.x daemons can communicate with Slurm commands
from version 14.03.x, 14.11.x and 15.08.x.
The same is true for state save files.
Slurm can be upgraded through two major or minor releases without loss of data
since the older state files are still recognized.
Slurm commands initiated under one version of Slurm can also continue to
execute and communicate with the Slurm daemons through two release upgrades
of the daemons.
Upgrades beyond two releases will result in unrecognized state information,
but intermediate upgrades can be performed to reformat the state information
and prevent its loss.
As new versions of Slurm are released, support for the oldest communication
protocols is removed from the code.</p>
<h2>Code Changes</h2>
<p>The code used for packing and unpacking RPCs can be mostly found in
<b>src/common</b>, although additional logic can also be found in each of
of the Slurm daemons (slurmctld, slurmd, and slurmdbd) plus some of the
plugins.</p>
<p>All RPCs and state save files contain Slurm version information.
This version information permits the server to recognize its format and
respond using a message format understood by the client.
When fields are added to or removed from existing RPCs, it is essential
that only the format of RPCs for the newest release of Slurm (which is still
under development) altered to avoid breaking pre-existing communication
protocols.
It may be necessary to add a new protocol version number to the code and
support for releases beyond two previous releases may be removed.
In the new code, copy the pack and unpack logic from the previous version of
the code and add new fields as needed.
Be sure to pack and unpack data in the identical order.
It is also important to keep in mind that when adding support for new fields
in an RPC protocol, that logic may need to be added to the older protocols
setting the new field values to a reasonable default value (e.g. NULL, 0).
For example, if a job is submitted using an old version of sbatch to a newer
slurmctld daemon, job specifications that are unknown to the old sbatch
should be set by the slurmctld daemon to reasonable values.
An example of the changes required are shown below.
In this trivial example, we want to add a new "max_nodes" field to the
message for Slurm version 15.08.x.</p>
<pre>
/*
* Original code in Slurm v2.5.x
*/
if (protocol_version >= SLURM_14_11_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
} else if (protocol_version >= SLURM_14_03_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
} else if (protocol_version >= SLURM_13_08_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
} else {
error("pack_whatever_msg: protocol_version "
"%hu not supported", protocol_version);
}
</pre>
<pre>
/*
* New code in Slurm v15.08.x
*/
if (protocol_version >= SLURM_15_08_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
pack32(msg->max_nodes, buffer);
} else if (protocol_version >= SLURM_14_11_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
pack32(msg->min_nodes, buffer);
} else if (protocol_version >= SLURM_14_03_PROTOCOL_VERSION) {
pack32(msg->job_id, buffer);
pack32(msg->user_id, buffer);
} else {
error("pack_whatever_msg: protocol_version "
"%hu not supported", protocol_version);
}
</pre>
<p style="text-align:center;">Last modified 05 May 2016</p>
<!--#include virtual="footer.txt"-->
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