Merge remote-tracking branch 'remotes/mdroth/tags/qga-pull-2020-04-15-tag' into staging

qemu-ga patch queue for hard-freeze

* enforce 48MB limit for guest-file-read to avoid memory allocation
  failures

# gpg: Signature made Wed 15 Apr 2020 15:23:48 BST
# gpg:                using RSA key CEACC9E15534EBABB82D3FA03353C9CEF108B584
# gpg:                issuer "mdroth@linux.vnet.ibm.com"
# gpg: Good signature from "Michael Roth <flukshun@gmail.com>" [full]
# gpg:                 aka "Michael Roth <mdroth@utexas.edu>" [full]
# gpg:                 aka "Michael Roth <mdroth@linux.vnet.ibm.com>" [full]
# Primary key fingerprint: CEAC C9E1 5534 EBAB B82D  3FA0 3353 C9CE F108 B584

* remotes/mdroth/tags/qga-pull-2020-04-15-tag:
  qga: Restrict guest-file-read count to 48 MB to avoid crashes
  qga: Extract qmp_guest_file_read() to common commands.c
  qga: Extract guest_file_handle_find() to commands-common.h
  Revert "prevent crash when executing guest-file-read with large count"

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>