From: Tejun Heo <htejun@gmail.com>
To: Jim Ramsay <jim.ramsay@gmail.com>, Jeff Garzik <jgarzik@pobox.com>
Cc: Linux-ide <linux-ide@vger.kernel.org>
Subject: Re: libata and hotplug status
Date: Sat, 02 Jul 2005 11:24:00 +0900 [thread overview]
Message-ID: <42C5FAC0.6070608@gmail.com> (raw)
In-Reply-To: <4789af9e050628135547fa5e14@mail.gmail.com>
Jim Ramsay wrote:
> I read at http://linux.yyz.us/sata/software-status.html that "libata
> does not support hotplug... yet", implying that it eventually would.
>
> I am very interested in the current state and progress of SATA hotplug
> support for libata-based drivers (specifically the 'sata_promise'
> driver for the Promise TX4 card). Has there been any preliminary work
> or discussion on this feature?
>
> How would it best be implemented? How much of a pain would it be to
> do? Are there any half-baked patches out there I can take a peek at
> or help with? Who can I prod to bump this up on the priority list for
> libata? What should I prod with?
>
Hi, Jim.
Hi, Jeff.
First of all, AFAIK, there's no previous work in implementing SATA
hotplug. I used to be pretty interested in implementing hot-plug for
libata. The problems are...
* libata runs under SCSI emulation, yet it tries to remain separate
from SCSI midlayer as much as possible (maybe for possible departure
from SCSI emulation someday). So, the probing procedure is done inside
libata layer when attaching a HBA and later SCSI discover commands are
just simulated making using SCSI midlayer's hot-plug support a little
bit difficult.
* SCSI midlayer's hotplug support is pretty brittle. The device state
model/host state model are broken in several aspects. (eg. multiple
entities may attempt to change a device's state but there's no
synchronization. You can mess it up pretty easily.) Also, there's no
generic hot-plug helpers in the SCSI midlayer which each specific
drivers can use with ease.
Well, I tried to fix SCSI midlayer and implement new device state
model but my patches haven't made it into SCSI devel tree (haven't given
up yet ;-), and I'm not really sure how Jeff thinks about changing SATA
probing such that it's more integrated with/tied to SCSI midlayer.
Maybe it's possible to implement hot plugging w/o strictly following
SCSI midlayer's probing model but, IMHO, it's gonna be messy.
Jeff, what do you think about this?
--
tejun
prev parent reply other threads:[~2005-07-02 2:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-06-28 20:55 libata and hotplug status Jim Ramsay
2005-07-02 2:24 ` Tejun Heo [this message]
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