Re: [PATCH 0/4] Remove un-needed 'major' registration when alloc_disk(0) is used.

From: NeilBrown
Date: Tue Mar 15 2016 - 18:15:42 EST

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.

> It seems like these could easily be converted in the same way so they'd use
> BLOCK_EXT_MAJOR for their major and have a bunch of dynamically assigned
> minors.
> Does this break something I'm not seeing?
> Yay for this series, by the way. :)

Thanks... two are in -next now (thank Dan) - I might poke the other two
in a week or two if nothing happens.


Attachment: signature.asc
Description: PGP signature