[RFC] nvme: set block size during namespace validation

[Christoph Hellwig]

On Thu, Dec 24, 2020 at 01:16:50AM +0900, Minwoo Im wrote:
> Hello,
> 
> On 20-12-23 16:49:04, Christoph Hellwig wrote:
> > set_blocksize just sets the block sise used for buffer heads and should
> > not be called by the driver.  blkdev_get updates the block size, so
> > you must already have the fd re-reading the partition table open?
> > I'm not entirely sure how we can work around this except by avoiding
> > buffer head I/O in the partition reread code.  Note that this affects
> > all block drivers where the block size could change at runtime.
> 
> Thank you Christoph for your comment on this.
> 
> Agreed.  BLKRRPART leads us to block_read_full_page which takes buffer
> heads for I/O.
> 
> Yes, __blkdev_get() sets i_blkbits of block device inode via
> set_init_blocksize.  And Yes again as nvme-cli already opened the block
> device fd and requests the BLKRRPART with that fd.  Also, __bdev_get()
> only updates the i_blkbits(blocksize) in case bdev->bd_openers == 0 which
> is the first time to open this block device.
> 
> Then, how about having NVMe driver prevent underflow case for the
> request->__data_len is smaller than the logical block size like:

Not sure this helps.  I think we need to fix this proper and in the
block layer.  The long term fix is to stop messing with i_blksize
at all, but that is going to take very long.

I think for now the only thing we can do is to set a flag in the
gendisk when the block size changes and then reject all I/O until
the next first open that sets the blocksize.