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SubjectRe: [PATCH 0/4] Remove un-needed 'major' registration when alloc_disk(0) is used.
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On 03/15/2016 03:15 PM, NeilBrown wrote:
> On Tue, Mar 15 2016, Ross Zwisler wrote:
>
>> On Thu, Mar 10, 2016 at 08:59:28AM +1100, NeilBrown wrote:
>>> When alloc_disk(0) is used, the ->major number is ignored and
>>> irrelevant. Yet several drivers register a major number anyway.
>>>
>>> This series of patches removes the pointless registrations. The pmem
>>> driver also does this, but a patch has already been sent for that
>>> driver.
>>>
>>> Note that I am not in a position to test these beyond simple compile
>>> testing.
>>>
>>> Thanks,
>>> NeilBrown
>>>
>>>
>>> ---
>>>
>>> NeilBrown (4):
>>> nvdimm/blk: don't allocate unused major device number
>>> nvdimm/btt: don't allocate unused major device number
>>> memstick: don't allocate unused major for ms_block
>>> NVMe: don't allocate unused nvme_major
>>>
>>>
>>> drivers/memstick/core/ms_block.c | 17 ++---------------
>>> drivers/nvdimm/blk.c | 18 +-----------------
>>> drivers/nvdimm/btt.c | 19 ++-----------------
>>> drivers/nvme/host/core.c | 16 +---------------
>>> 4 files changed, 6 insertions(+), 64 deletions(-)
>>
>> There are several other drivers that allocate a major, but then use it for
>> some small number of minors (1 for null_blk.c and 16 for virtio_blk.c). They
>> both have GENHD_FL_EXT_DEVT set, so I think what happens is that after we
>> exhaust the allocated minors they hop over to having BLOCK_EXT_MAJOR as a
>> major and a dynamically assigned minor.
>
> null_blk looks like it would be safe to convert - it is just used for
> testing. Jens Axboe would probably know for sure.
>
> virtio_blk is a much older and there may will be code which has some
> sort of expectations about minor numbers. I think it would not be worth
> the risks to change it.

Agree on both - null_blk can be trivially converted, and I too would be
worried about virt_blkio changes breaking existing assumptions.

--
Jens Axboe

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