Hi, Jeff.
Jeff Garzik wrote:
Tejun Heo wrote:
Hello, fellow SCSI/ATA developers.
This is the first draft of SCSI EH document. This document tries to
describe how SCSI EH works and what choirs should be done to maintain
SCSI midlayer integrity. It's intended that this document can be used
as reference for implementing either fine-grained EH callbacks or
single eh_strategy_handler() callback.
I'm pretty sure that I've screwed up in (hopefully) several places,
so please correct me. Also, I have several places where I'm not sure
or have questions, those are marked with *VERIFY* and *QUESTION*
respectively. If you know the answer, please let me know.
Seems sane to me at first glance.
- EH_RESET_TIMER
This indicates that more time is required to finish the
command. Timer is restarted. This action is counted as a
retry and only allowed scmd->allowed + 1(!) times. Once the
limit is reached, EH_NOT_HANDLED action is taken.
*NOTE* This action is racy as the LLDD could finish the scmd
after the timeout has expired but before it's added back. In
such cases, scsi_done() would think that timeout has occurred
and return without doing anything. We lose completion and the
command will time out again.
hmmmm
[2-2-2] Post hostt->eh_strategy_handler() SCSI midlayer conditions
The following conditions must be true on exit from the handler.
- shost->host_failed is zero.
- Each scmd's eh_eflags field is cleared.
- Each scmd is in such a state that scsi_setup_cmd_retry() on the
scmd doesn't make any difference.
- shost->eh_cmd_q is cleared.
- Each scmd->eh_entry is cleared. (*VERIFY* This is currently not
necessary for correct operation, but keep them cleared anyway for
consistency.)
Both all the list-heads need to be cleared, otherwise there may be list
corruption next time the element is added to the list_head.
scmd->eh_entry is never used as list head. It's always used as list
entry. So, technically, it needs not be cleared, I think. No? The
problem we had was w/ shost->eh_cmd_q not being cleared.
Thanks.
--
tejun
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