Hi,
Sorry to cc so many FS guys. I am a lowly SCSI guy :), so I have no idea
what lists you guys normally hang out on.
The problem is dm-multipath needs more information about why a IO is
being failed. If it gets a error because a cable went bad, then we want
to retry a new path right away. If it gets a error because the device is
dead, then we want to fail it upwards.
Block layer drivers currently return a errno.h type of error code like
-EIO or -EOPNOTSUPP to blk_end_request/blk_end_request_all and friends.
So a long time ago, I tried to just add new errno values for the block
layer to use (http://marc.info/?l=linux-kernel&m=107715299008231&w=2).
People did not like this for various reasons.
Next, I tried adding new block layer error codes
(http://marc.info/?l=linux-kernel&m=107961883915068&w=2 and again here
http://marc.info/?l=linux-scsi&m=112487427230642&w=2 and actually I
modified those again a couple times but cannot find the links). My
concern with the approach in these patches is that while they work well
for errors that dm-multipath needs to handle, I have no idea what File
Systems devs need. Also I think this would be useful for RAID.
Now, at work I have lots of bugzillas so I can finally spend some time
at work to finish this up, and I want to know what developers need. If
the lower layers can tell you what failed (device or connection to a
device or driver) and if the lower layers thought the problem was
retryable or not from its perspective is that good enough. Something
like this http://marc.info/?l=linux-scsi&m=112487427230642&w=2 ?
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