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dax: Modify bdev_dax_pgoff() to handle NULL bdev

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virtiofs does not have a block device but it has dax device.
Modify bdev_dax_pgoff() to be able to handle that.

If there is no bdev, that means dax offset is 0. (It can't be a partition
block device starting at an offset in dax device).

This is little hackish. There have been discussions about getting rid
of dax not supporting partitions.

https://lore.kernel.org/linux-fsdevel/20200107125159.GA15745@infradead.org/

IMHO, this path can easily break exisitng users. For example
ioctl(BLKPG_ADD_PARTITION) will start breaking on block devices
supporting DAX. Also, I personally find it very useful to be able to
partition dax devices and still be able to use DAX.

Alternatively, I tried to store offset into dax device information in iomap
interface, but that got NACKed.

https://lore.kernel.org/linux-fsdevel/20200217133117.GB20444@infradead.org/

I can't think of a good path to solve this issue properly. So to make
progress, it seems this patch is least bad option for now and I hope
we can take it.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Cc: "Weiny, Ira" <ira.weiny@intel.com>
Cc: linux-nvdimm@lists.01.org
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Vivek Goyal 2020-08-19 18:19:39 -04:00 committed by Miklos Szeredi
parent 27bd6129a4
commit 1a9d5d4059
1 changed files with 2 additions and 1 deletions
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3
drivers/dax/super.c
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@ -46,7 +46,8 @@ EXPORT_SYMBOL_GPL(dax_read_unlock);
int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
pgoff_t *pgoff)
{
phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;
sector_t start_sect = bdev ? get_start_sect(bdev) : 0;
phys_addr_t phys_off = (start_sect + sector) * 512;
if (pgoff)
*pgoff = PHYS_PFN(phys_off);