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[Qemu-devel] Machine-readable or parseable qemu output
From: |
Amit Shah |
Subject: |
[Qemu-devel] Machine-readable or parseable qemu output |
Date: |
Wed, 14 Jan 2009 16:40:05 +0530 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
Hello,
Continuing from the thread at [1], building on Daniel's suggestions, I
have jot down a few points as to how a libqemumonitor API could be
developed.
To recap, there has to be an interface to the qemu monitor in
a way that wouldn't break even if the monitor output changes. This API
will remain the same, so that consumers (libvirt, etc) can safely
integrate with the monitor.
Please see Dan's email at [1] to get the background details.
[1] http://www.mail-archive.com/address@hidden/msg14615.html
Here are some initial thoughts. Comments?
- Have a libqemumonitor.so that will abstract out output from qemu and
provide a machine-readble output for the consumer
- Registering with a particular qemu instance:
- qemu_instance = attach_to_qemu("/path/to/socket");
- The strings in qemu monitor can change but the libqemumonitor has to
change accordingly as well to keep the API consistent.
- The API could be something like:
- execute_qemu_command(qemu_instance, command, args...);
This will then return with a value of:
- 0: Success (no output)
- -ve: Failure
- +ve: Log level type from QEMU monitor output (see below)
- For qemu, a loglevel can be added so that the message output is
disciplined (as seen in kernel printk messages):
- term_printf(QINFO, "Beginning migration\n");
- term_printf(QERR, "Migration failed\n");
- -ve return values can be reserved to indicate that the link with the qemu
monitor went down or some other problem with the libqemumonitor and
the monitor interface
- In addition to the return value seen of the loglevel type from the
monitor, there can be additional return values that can be provided
based on the command executed. This can be queried by:
- get_info_on_prev_command(qemu_instance, &ret);
- This can give command-specific return values, like success,
invalid parameter, etc.
- The string generated by qemu monitor output should never be exposed to
the consumer
- Some monitor commands will generate some string that might be of use
to the consumer. Such a string will be passed to the consumer via some
other api, like
- get_string_from_last_command(qemu_instance, some_context);
- There might be output that's asynchronous to the command. Finding the
correlation between the command and the output should not be the
library's job; an async_socket can be created per qemu instance and
the consumer can select() on this socket to poll for data. Whenever
some information becomes available, we can push it out. If the qemu
output would contain more information for async output, this can be
passed on to the consumer.
Amit.
- [Qemu-devel] Machine-readable or parseable qemu output,
Amit Shah <=
[Qemu-devel] Re: Machine-readable or parseable qemu output, Avi Kivity, 2009/01/14
[Qemu-devel] Re: Machine-readable or parseable qemu output, Richard W.M. Jones, 2009/01/14