[RFC PATCH v2 0/8] block-backend: Introduce I/O hang

[Jiahui Cen]

A VM in the cloud environment may use a virutal disk as the backend storage,
and there are usually filesystems on the virtual block device. When backend
storage is temporarily down, any I/O issued to the virtual block device will
cause an error. For example, an error occurred in ext4 filesystem would make
the filesystem readonly. However a cloud backend storage can be soon recovered.
For example, an IP-SAN may be down due to network failure and will be online
soon after network is recovered. The error in the filesystem may not be
recovered unless a device reattach or system restart. So an I/O rehandle is
in need to implement a self-healing mechanism.

This patch series propose a feature called I/O hang. It can rehandle AIOs
with EIO error without sending error back to guest. From guest's perspective
of view it is just like an IO is hanging and not returned. Guest can get
back running smoothly when I/O is recovred with this feature enabled.

v1->v2:
* Rebase to fix compile problems.
* Fix incorrect remove of rehandle list.
* Provide rehandle pause interface.

Jiahui Cen (8):
  block-backend: introduce I/O rehandle info
  block-backend: rehandle block aios when EIO
  block-backend: add I/O hang timeout
  block-backend: add I/O rehandle pause/unpause
  block-backend: enable I/O hang when timeout is set
  virtio-blk: pause I/O hang when resetting
  qemu-option: add I/O hang timeout option
  qapi: add I/O hang and I/O hang timeout qapi event

 block/block-backend.c          | 300 +++++++++++++++++++++++++++++++++
 blockdev.c                     |  11 ++
 hw/block/virtio-blk.c          |   8 +
 include/sysemu/block-backend.h |   5 +
 qapi/block-core.json           |  26 +++
 5 files changed, 350 insertions(+)

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2.28.0