Re: [PATCH v2 0/3] scsi: ufs & ums-*: fix module reference counting

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2015-01-08 0:09 GMT+09:00 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>:
> On Wed, 7 Jan 2015, Christoph Hellwig wrote:
>
>> On Wed, Jan 07, 2015 at 11:02:59PM +0900, Akinobu Mita wrote:
>> > While accessing a scsi_device, the use count of the underlying LLDD module
>> > is incremented.  The module reference is retrieved through .module field of
>> > struct scsi_host_template.
>> >
>> > This mapping between scsi_device and underlying LLDD module works well
>> > except some scsi drivers (ufs and unusual usb storage drivers).  These
>> > drivers consist with core driver and actual LLDDs, and scsi_host_template
>> > is defined in the core driver.  So the actual LLDDs can be unloaded even if
>> > the scsi_device is being accessed.
>>
>> Why don't ufs and usb-storage define the host templates in the sub drivers?
>> That's what libata or the mpt fusion driver do.
>
> Originally the subdrivers were all part of usb-storage.  When they were
> split out into separate modules, there didn't seem to be any need to
> copy the host template into each one.  (Especially since some of the
> method pointers in the host template refer to routines in usb-storage
> itself, not in the subdrivers.)  The fact that the .module member was
> no longer adequate escaped our notice at the time.

For ufs, the reason why a host template is shared by sub drivers is similar
to usb-storage.  Originally there was only a single pci driver for ufs.
When platform driver for ufs was introduced, it was split into core driver
(ufshcd) and sub drivers (ufshcd-pci and ufshcd-pltfrm).  They require
exactly the same host template.

Is there any other preferable way to fix this problem?  The first time I
found this in ufs driver, I was trying to fix it by merging core and sub
drivers into a single compound module.  But I realized that usm-* drivers
have the same problem, then I decided to propose what this patch series do
instead.
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