[PATCH v4 0/7] block: Add retry for werror=/rerror= mechanism

[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. 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.

v3->v4:
* Adapt to werror=/rerror= mechanism.

v2->v3:
* Add a doc to describe I/O hang.

v1->v2:
* 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

Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
Signed-off-by: Ying Fang <fangying1@huawei.com>

Jiahui Cen (7):
  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

 block/block-backend.c          | 66 ++++++++++++++++++++
 blockdev.c                     | 52 +++++++++++++++
 hw/block/block.c               | 10 +++
 hw/block/virtio-blk.c          | 19 +++++-
 include/hw/block/block.h       |  7 ++-
 include/sysemu/block-backend.h | 10 +++
 qapi/block-core.json           |  4 +-
 7 files changed, 162 insertions(+), 6 deletions(-)

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2.28.0