On 11/17/2010 05:01 AM, Tejun Heo wrote:
Hello, Jeff, Linus.
On 11/17/2010 09:08 AM, Jeff Garzik wrote:
Looking solely at the SCSI code (ie. ignoring LLD code), it seems
like the magic number zero for serial_number is signaling a boolean
condition "are we an EH command?"
EH tests this at the very beginning of the abort/reset/explode error
handling sequence, presumably to avoid recursive EH invocations
(scsi_try_to_abort_cmd).
So maybe an EH expert (Tejun?) can correct me here, but I think we
may be able to completely the lock/get-serial/unlock sequence from
libata, as long as scsi_init_cmd_errh() reliably sets an "I am an EH
command" flag.
Would be nice if true...
Yeah, it's actually nice (for once). libata doesn't use or care about
scmd->serial_number at all. The SCSI EH path you mentioned above is
not applicable as libata implements its eh_strategy_handler and SCSI
only calls scsi_try_to_abort_cmd() for the default EH handler,
scsi_unjam_host().
We'll need to test a bit to make sure everything is okay but I'm
fairly certain removing it won't break anything fundamental. If
something breaks at all, it would be some silly easy-to-fix thing.
It would be surprising if there is breakage, because serial_number is
only tested in two places in the generic kernel:
scsi_cmd_get_serial() -- where it simply avoids the zero value -- and
scsi_try_to_abort_cmd().
Jeff
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