[RFC] nvme: set block size during namespace validation

[Minwoo Im]

On 20-12-23 17:27:37, Christoph Hellwig wrote:
> 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.

Agreed.

> 
> 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.

Let me prepare work around patch for this issue soon.

Thanks!