Currently, qemu-ga may die/get killed/go away for whatever reason after
guest-fsfreeze-freeze has been issued, and before guest-fsfreeze-thaw
has been issued. This means the only way to unfreeze the guest is via
VNC/network/console access, but obtaining that access after-the-fact can
often be very difficult when filesystems are frozen. Logins will almost
always hang, for instance. In many cases the only recourse would be to
reboot the guest without any quiescing of volatile state, which makes
this a corner-case worth giving some attention to.
A likely failsafe for this situation would be to use a watchdog to
restart qemu-ga if it goes away. There are some precautions qemu-ga
needs to take in order to avoid immediately hanging itself on I/O,
however, namely, we must disable logging and defer to processing/creation
of user-specific logfiles, along with creation of the pid file if we're
running as a daemon. We also need to disable non-fsfreeze-safe commands,
as we normally would when processing the guest-fsfreeze-freeze command.
To track when we need to do this in a way that persists between multiple
invocations of qemu-ga, we create a file on the guest filesystem before
issuing the fsfreeze, and delete it when doing the thaw. On qemu-ga
startup, we check for the existance of this file to determine
the need to take the above precautions.
We're forced to do it this way since a more traditional approach such as
reading/writing state to a dedicated state file will cause
access/modification time updates, respectively, both of which will hang
if the file resides on a frozen filesystem. Both can occur even if
relatime is enabled. Checking for file existence will not update the
access time, however, so it's a safe way to check for fsfreeze state.
An actual watchdog-based restart of qemu-ga can itself cause an access
time update that would thus hang the invocation of qemu-ga, but the
logic to workaround that can be handled via the watchdog, so we don't
address that here (for relatime we'd periodically touch the qemu-ga
binary if the file $qga_statedir/qga.state.isfrozen is not present, this
avoids qemu-ga updates or the 1 day relatime threshold causing an
access-time update if we try to respawn qemu-ga shortly after it goes
away)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Currently we rely on fsfreeze/thaw commands disabling/enabling logging
then having other commands check whether logging is disabled to avoid
executing if they aren't safe for running while a filesystem is frozen.
Instead, have an explicit whitelist of fsfreeze-safe commands, and
consolidate logging and command enablement/disablement into a pair
of helper functions: ga_set_frozen()/ga_unset_frozen()
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
guest-sync leaves it as an exercise to the user as to how to reliably
obtain the response to guest-sync if the client had previously read in a
partial response (due qemu-ga previously being restarted mid-"sentence"
due to reboot, forced restart, etc).
qemu-ga handles this situation on its end by having a client precede
their guest-sync request with a 0xFF byte (invalid UTF-8), which
qemu-ga/QEMU JSON parsers will treat as a flush event. Thus we can
reliably flush the qemu-ga parser state in preparation for receiving
the guest-sync request.
guest-sync-delimited provides the same functionality for a client: when
a guest-sync-delimited is issued, qemu-ga will precede it's response
with a 0xFF byte that the client can use as an indicator to flush its
buffer/parser state in preparation for reliably receiving the
guest-sync-delimited response.
It is also useful as an optimization for clients, since, after issuing a
guest-sync-delimited, clients can safely discard all stale data read
from the channel until the 0xFF is found.
More information available on the wiki:
http://wiki.qemu.org/Features/QAPI/GuestAgent#QEMU_Guest_Agent_Protocol
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
As the command name implies, this command suspends the guest to disk.
The suspend operation is implemented by two functions: bios_supports_mode()
and guest_suspend(). Both functions are generic enough to be used by
other suspend modes (introduced by next commits).
Both functions will try to use the scripts provided by the pm-utils
package if it's available. If it's not available, a manual method,
which consists of directly writing to '/sys/power/state', will be used.
To reap terminated children, a new signal handler is installed in the
parent to catch SIGCHLD signals and a non-blocking call to waitpid()
is done to collect their exit statuses. The statuses, however, are
discarded.
The approach used to query the guest for suspend support deserves some
explanation. It's implemented by bios_supports_mode() and shown below:
qemu-ga
|
create pipe
|
fork()
-----------------
| |
| |
| fork()
| --------------------------
| | |
| | |
| | exec('pm-is-supported')
| |
| wait()
| write exit status to pipe
| exit
|
read pipe
This might look complex, but the resulting code is quite simple.
The purpose of that approach is to allow qemu-ga to reap its children
(semi-)automatically from its SIGCHLD handler.
Implementing this the obvious way, that's, doing the exec() call from
the first child process, would force us to introduce a more complex way
to reap qemu-ga's children. Like registering PIDs to be reaped and
having a way to wait for them when returning their exit status to
qemu-ga is necessary. The approach explained above avoids that complexity.
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
This allows qemu-ga to function as a Windows service:
- to install the service (will auto-start on boot):
qemu-ga --service install
- to start the service:
net start qemu-ga
- to stop the service:
net stop qemu-ga
- to uninstall service:
qemu-ga --service uninstall
Original patch by Gal Hammer <ghammer@redhat.com>
This adds a win32 channel implementation that makes qemu-ga functional
on Windows using virtio-serial (unix-listen/isa-serial not currently
implemented). Unlike with the posix implementation, we do not use
GIOChannel for the following reasons:
- glib calls stat() on an fd to check whether S_IFCHR is set, which is
the case for virtio-serial on win32. Because of that, a one-time
check to determine whether the channel is readable is done by making
a call to PeekConsoleInput(), which reports the underlying handle is
not a valid console handle, and thus we can never read from the
channel.
- if one goes as far as to "trick" glib into thinking it is a normal
file descripter, the buffering is done in such a way that data
written to the output stream will subsequently result in that same
data being read back as if it were input, causing an error loop.
furthermore, a forced flush of the channel only moves the data into a
secondary buffer managed by glib, so there's no way to prevent output
from getting read back as input.
The implementation here ties into the glib main loop by implementing a
custom GSource that continually submits asynchronous/overlapped I/O to
fill an GAChannel-managed read buffer, and tells glib to poll the
corresponding event handle for a completion whenever there is no
data/RPC in the read buffer to notify the main application about.
Various stubs and #ifdefs to compile for Windows using mingw
cross-build. Still has 1 linker error due to a dependency on the
forthcoming win32 versions of the GAChannel/transport class.
This is mostly in preparation for the win32 port, which won't use
GIO channels for reasons that will be made clearer later. Here the
GAChannel class is just a loose wrapper around GIOChannel
calls/callbacks, but we also roll in the logic/configuration for
various channel types and managing unix socket connections, which makes
the abstraction much more complete and further aids in the win32 port
since isa-serial/unix-listen will not be supported initially.
There's also a bit of refactoring in the main logic to consolidate the
exit paths so we can do common cleanup for things like pid files, which
weren't always cleaned up previously.
This adds a command-line option, -b/--blacklist, that accepts a
comma-seperated list of RPCs to disable, or prints a list of
available RPCs if passed "?".
In consequence this also adds general blacklisting and RPC listing
facilities to the new QMP dispatch/registry facilities, should the
QMP monitor ever have a need for such a thing.
Ideally, to avoid support/compatability issues in the future,
blacklisting guest agent functionality will be the exceptional
case, but we add the functionality here to handle guest administrators
with specific requirements.
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Reviewed-by: Andreas Färber <andreas.faerber@web.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
g_strcmp0 isn't in all version of glib 2.0, so don't use it to avoid
build breakage on older distros.
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
As far as I can tell, there isn't a dependency on gthread. Also, the only use
of gio was to enable GSocket to accept a unix domain socket.
Since GSocket isn't available on OpenSuSE 11.1, let's just remove that
dependency.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This is the actual guest daemon, it listens for requests over a
virtio-serial/isa-serial/unix socket channel and routes them through
to dispatch routines, and writes the results back to the channel in
a manner similar to QMP.
A shorthand invocation:
qemu-ga -d
Is equivalent to:
qemu-ga -m virtio-serial -p /dev/virtio-ports/org.qemu.guest_agent.0 \
-f /var/run/qemu-ga.pid -d
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@gmail.com>
Michael Roth
Luiz Capitulino
Stefan Weil
Stefan Weil
Anthony Liguori