Merge remote-tracking branch 'kwolf/for-anthony' into staging

Merge remote-tracking branch 'kwolf/for-anthony' into staging

* kwolf/for-anthony:
  AHCI: Masking of IRQs actually masks them
  sheepdog: fix co_recv coroutine context
  AHCI: Fix port reset race
  rewrite QEMU_BUILD_BUG_ON
  qcow2: Keep unknown header extension when rewriting header
  qcow2: Update whole header at once
  vpc: Round up image size during fixed image creation
  vpc: Add support for Fixed Disk type
  iSCSI: add configuration variables for iSCSI
  qemu-io: add write -z option for bdrv_co_write_zeroes
  qed: add .bdrv_co_write_zeroes() support
  qed: replace is_write with flags field
  block: perform zero-detection during copy-on-read
  block: add .bdrv_co_write_zeroes() interface
  cutils: extract buffer_is_zero() from qemu-img.c