block: vhdx - fix reading beyond pointer during image creation

In vhdx_create_metadata(), we allocate 40 bytes to entry_buffer for
the various metadata table entries.  However, we write out 64kB from
that buffer into the new file.  Only write out the correct 40 bytes.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
block: Validate node-name

The device_name of a BlockDriverState is currently checked because it is
always used as a QemuOpts ID and qemu_opts_create() checks whether such
IDs are wellformed.

node-name is supposed to share the same namespace, but it isn't checked
currently. This patch adds explicit checks both for device_name and
node-name so that the same rules will still apply even if QemuOpts won't
be used any more at some point.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Benoit Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
async: aio_context_new(): Handle event_notifier_init failure

On a system with a low limit of open files the initialization
of the event notifier could fail and QEMU exits without printing any
error information to the user.

The problem can be easily reproduced by enforcing a low limit of open
files and start QEMU with enough I/O threads to hit this limit.

The same problem raises, without the creation of I/O threads, while
QEMU initializes the main event loop by enforcing an even lower limit of
open files.

This commit adds an error message on failure:

 # qemu [...] -object iothread,id=iothread0 -object iothread,id=iothread1
 qemu: Failed to initialize event notifier: Too many open files in system

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>