Hello, Brian.
Brian King wrote:
Making the array dynamically-sized isn't difficult at all; however, the
current libata code assumes that ata_host->ports[] array is packed - ie.
no intervening empty entry. Can SAS keep this restriction or does it
need more flexibility?
This could be made to work with the addition of a new API. Rather than
having just ata_sas_port_destroy, we would need ata_sas_port_delete
and ata_sas_port_free. ata_sas_port_delete would remove the port from
the ata_host and do everything except free the ata port since there
could still be references to it. Then ata_sas_port_free would get called
once all the references were deleted.
I see.
Hmmm.... I was kind of hoping SAS could use ata_host_alloc() and store
its pointer and then later release it w/ ata_host_free(), hmmm.. maybe
you can call ata_host_free from ->slave_destroy?. That gives libata
more control over the host structure (e.g. if we implement dynamic ports
array, it needs to be freed too). Port lifetime rules aren't changed by
these updates and host free does need some changes but IMHO that
shouldn't be difficult.
The current design for SAS is to have a single ata_host per scsi host.
This means the ata_host is really tied to the object lifetime rules
of the scsi host. In the current SAS code, ata_host_set does not get allocated
as a separate piece of memory, but rather as part of the scsi_host
object. This means the memory for the ata_host doesn't get freed until
the last reference to the scsi host is released. Making ata_host
a separate allocation changes these rules and forces the caller to
know when to free the ata_host memory, which they currently do not know.
You're right. I was confused that ->slave_destroy() is called on host
release. SCSI doesn't have host release callback. What do you think
about adding a host release callback? That should make things easier
and it is generally useful.
In order to do what you are proposing, I think we would need to add
some refcounting to the ata_host object. Each allocated ata_port would
get a reference to its parent ata_host and would put a reference when the
port is freed. Otherwise I am concerned that we would end up in the situation
where the ata_host is freed before all the ata ports and the scsi_host is
freed. It might be appropriate to create an ata_host class device and
an ata_port class device...
Or we can just keep ata_host_init() and let sas allocate ata_host as
part of SCSI host and free all dynamic stuff when all ports are
detached. It's a bit hacky but should work for the time being.
Hmmm.... I see. Something like ata_dev_attach(adev) after initialized
by SAS maybe?
Possibly. Are you proposing that ata_dev_attach would then end up calling
scsi_add_device after doing the ATA initialization stuff?
For SAS, libata isn't controlling SCSI host, so I think it's more
logical to leave SCSI devices to SAS too. Would that make much difference?
Thanks.
--
tejun
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