A not too small part of the recent CVEs were DoS scenarios by letting
qemu abort with too large memory allocations. We generally "fixed" these
cases by setting some limits on values read from image files that
influence the size of allocations.
Because we still need to allow reading large images, this works only to
a certain degree and we still can get fairly large allocations, which
are not unthinkable to fail on some machines.
This series converts potentially large allocations to g_try_malloc() and
friends and handles failure gracefully e.g. by returning -ENOMEM. This
may cause hot-plug of a new disk or individual requests to fail, but the
VM as a whole can keep running.