[Qemu-block] question：about introduce a new feature named “I/O hang”

[wangjie (P)]

Hi, everybody：

I developed a feature named "I/O hang"，my intention is to solve the 
problem like that：
If the backend storage media of VM disk is far-end storage like IPSAN or 
FCSAN, storage net link will always disconnection and
make I/O requests return EIO to Guest, and the status of filesystem in 
Guest will be read-only, even the link recovered
after a while, the status of filesystem in Guest will not recover.

So I developed a feature named "I/O hang" to solve this problem, the 
solution like that：
when some I/O requests return EIO in backend, "I/O hang" will catch the 
requests in qemu block layer and
insert the requests to a rehandle queue but not return EIO to Guest, the 
I/O requests in Guest will hang but it does not lead
Guest filesystem to be read-only, then "I/O hang" will loop to rehandle 
the requests for a period time(ex. 5 second) until the requests
not return EIO(when backend storage link recovered).

In addition to the function as above, "I/O hang" also can sent event to 
libvirt after backend storage status changed.

configure methods:
1. "I/O hang" ability can be configured for each disk as a disk attribute.
2. "I/O hang" timeout value also can be configured for each disk, when 
storage link not recover in timeout value,
   "I/O hang" will disable rehandle I/O requests and return EIO to Guest.


Are you interested in the feature?  I intend to push this feature to 
qemu org, what's your opinion?