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[PATCH v5 0/9] block: Add retry for werror=/rerror= mechanism

From: Jiahui Cen
Subject: [PATCH v5 0/9] block: Add retry for werror=/rerror= mechanism
Date: Fri, 5 Feb 2021 18:13:06 +0800

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. In production environment, 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. However,
the error in the filesystem may not be recovered unless a device reattach
or system restart. Thus an I/O retry mechanism is in need to implement a
self-healing system.

This patch series propose to extend the werror=/rerror= mechanism to add
a 'retry' feature. It can automatically retry failed I/O requests on error
without sending error back to guest, and guest can get back running smoothly
when I/O is recovred.

* Add document for 'retry' in qapi.
* Support werror=/rerror=retry for scsi-disk.
* Pause retry when draining.

* Adapt to werror=/rerror= mechanism.

* Add a doc to describe I/O hang.

* Rebase to fix compile problems.
* Fix incorrect remove of rehandle list.
* Provide rehandle pause interface.

REF: https://lists.gnu.org/archive/html/qemu-devel/2020-10/msg06560.html

Jiahui Cen (9):
  qapi/block-core: Add retry option for error action
  block-backend: Introduce retry timer
  block-backend: Add device specific retry callback
  block-backend: Enable retry action on errors
  block-backend: Add timeout support for retry
  block: Add error retry param setting
  virtio_blk: Add support for retry on errors
  scsi-bus: Refactor the code that retries requests
  scsi-disk: Add support for retry on errors

 block/block-backend.c          | 68 ++++++++++++++++++++
 blockdev.c                     | 52 +++++++++++++++
 hw/block/block.c               | 10 +++
 hw/block/virtio-blk.c          | 21 +++++-
 hw/scsi/scsi-bus.c             | 16 +++--
 hw/scsi/scsi-disk.c            | 16 +++++
 include/hw/block/block.h       |  7 +-
 include/hw/scsi/scsi.h         |  1 +
 include/sysemu/block-backend.h | 10 +++
 qapi/block-core.json           |  9 ++-
 10 files changed, 199 insertions(+), 11 deletions(-)


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