cam patch: reducing logging output for 'normal' failures

[Andriy Gapon]

on 24/11/2010 10:50 Alexander Motin said the following:
> Bruce Cran wrote:
>> I came across http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/119668
>> which contains a patch to reduce the verbosity of output from the cam
>> subsystem. cam has a tendancy to be a bit spammy when it 
>> comes across fairly normal situations such as the tray having been left 
>> open, or there just not being a disc present. For example:
>>
>> (probe0:umass-sim0:0:0:0): TEST UNIT READY. CDB: 0 0 0 0 0 0 
>> (probe0:umass-sim0:0:0:0): CAM status: SCSI Status Error
>> (probe0:umass-sim0:0:0:0): SCSI status: Check Condition
>> (probe0:umass-sim0:0:0:0): SCSI sense: NOT READY asc:3a,1 (Medium not present - tray closed)
>> cd0 at umass-sim0 bus 0 scbus9 target 0 lun 0
>> cd0: <DVDRW USB H16X B02T> Removable CD-ROM SCSI-0 device 
>> cd0: 40.000MB/s transfers
>> cd0: Attempt to query device size failed: NOT READY, Medium not present
>> - tray closed
>>
>> The first message, "Medium not present - tray closed" is unnecessary 
>> since it's repeated a few lines later and can look as though 
>> there's a real problem. I've attached an updated patch which adds the 
>> the tray open warning too.
>>
>> Any comments?
> 
> I have feeling that it could depend on consumer: whether it wants kernel
> should log it's errors or not. For example, it could be reasonable to
> log errors for kernel drivers not doing it by themselves, such as "ad"
> or "ada" (another question why they couldn't do it). Same time it is
> probably impractical to log errors for requests coming from user-level
> via "pass" driver.

So how would kernel know would a consumer wants?
I think that kernel should log only the conditions that it knows to be fatal and
serious.  The rest is up to the consumers.  Which, BTW, should have a better
picture of what's going and should be able to produce a more meaningful message.

I think that Bruce's example above demonstrates this quite good - compare
"umass-sim0" messages with "cd0" messages.

-- 
Andriy Gapon