Bart Van Assche [off-list ref] 于2018年12月7日周五 上午12:22写道：

On Wed, 2018-12-05 at 22:17 +0800, Weiping Zhang wrote:

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+Description:
+             io_timeout is a request’s timeouts at block layer in
+             milliseconds. When the underlying driver starts processing
+             a request, the generic block layer will start a timer, if
+             this request cannot be completed in io_timeout milliseconds,
+             a timeout event will occur.

Sorry but I think this description is still somewhat confusing. How about
changing that description into the following?

        io_timeout is the request timeout in milliseconds. If a request does not
        complete in this time then the block driver timeout handler is invoked.
        That timeout handler can decide to retry the request, to fail it or to
        start a device recovery strategy.

Sorry for late reply, thanks for your suggestion I'll post it in V4.

Bart.

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Is there a simple way do that ?

How about checking the timeout member of struct blk_mq_ops for blk-mq and
checking the rq_timed_out_fn member in struct request_queue for the legacy
block layer?

Just the former given that the legacy code is gone in for-next.

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Shall we return -ENOTSUPP when user read/write this attribute when
driver has no timeout handler ?

A much more elegant solution is to introduce a sysfs attribute group for the
io_timeout attribute and to make that group visible only if a timeout handler
has been defined. See e.g. disk_attr_group in block/genhd.c for an example.

Agreed, that is the way to go.

OK, I'll do that.

Thanks
Weiping