Make the core swap code calculate sis->pages, nr_extents and the span,
re-set sis->max based on it and don't require passing the current offset
into the swap file to swap_add_extent as all that can trivially be
calculated internally.  Also truncate the spans based on the available
information.

All this removes a lot of boilerplate code in the callers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

The swap operations have nothing to do with the address_space, which is
used for pagecache operations.  Move them to struct file_operations
instead.  This will allow moving the block device special cases into
block/fops.c subsequently.

Pass struct file first to ->swap_activate as file operations typically
get the file or iocb as first argument and use swap_activate instead of
swapfile_activate in all names to be consistent.

Note that while the trivial iomap wrappers are moved to a new file when
applicable to keep them local to the file operation instances, complex
implementation are kept in their existing place.  It might be worth to
move them in follow-on patches if the maintainers desire so.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

Various swap code assumes it runs either on a block device or on a
regular file.  Make this restriction explicit using checks right
after opening the file.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

Reflow setup_swap_extents so that the flag checking is not conditional on
a swap_activate method.  This is currently a no-op because the swapoff
code still checks the presence of a swap_deactivate method, but it
simplifies adding a new check, and also makes the SWP_ACTIVATED flag
more consistent.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

Make use of the abstractions we have.  This is a preparation for
moving more special casing down into block/.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

Don't blindly pass the value from the swap header to swap_add_extent,
but instead the device size rounded down to page granularity.  This
activated the sanity checking in the core code that catches a too large
value in the swap header.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

add_swap_extent already coalesces multiple extents, no need to duplicate
that in the caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Only the file operation method knows what block device we'll swap
to.  So move down setting sis->bdev and the special blockdev flag
into ->swap_activate.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Add a helper abstracting away the low-level details of enabling
fs_ops-based swapping.  This prepares for taking swap_info_struct
private.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>

struct swap_extent is only used inside of mm/swapfile.c, so move it
there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>