it encounters an error it returns an error from the ioctl.
Ignore any errors when using the FD_FORM ioctl.

PR:	kern/103862
MFC after:	3 days

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by:	ru
Approved by:	philip, ed (mentors)

The kernel does not log floppy media errors anymore.

In fdcontrol, do always open the file descriptor in read-only mode so
it can operate on read-only media, as there is no longer a separate
control device to operate on.

fdcontrol/fdcontrol.c:
	- Add const constraint to an intermediate value
	  which is not supposed to be changed elsewhere.
fdread/fdread.c:
	- Use _devname in favor of devname to avoid name
	  conflicit.
	- -1 is less than any positive number so in order
	  to get the block to function, we should get the
	  block a little earlier.
	- Cast to remove signed when we are sure that a
	  return value is positive, or is compared with
	  an positive number (tracknumber of a floppy
	  disk is not likely to have UINT_MAX/2 anyway)
fdread/fdutil.c:
	- Use more specific initializer
fdwrite/fdwrite.c:
	- Use static on format_track since it's not
	  referenced in other places.
	- Use const char* to represent string constant.

Bump WARNS accordingly.

	Centralize the fdctl_wr() function by adding the offset in
	the resource to the softc structure.

	Bugfix: Read the drive-change signal from the correct place:
	same place as the ctl register.

	Remove the cdevsw{} related code and implement a GEOM class.

	Ditch the state-engine and park a thread on each controller
	to service the queue.

	Make the interrupt FAST & MPSAFE since it is just a simple
	wakeup(9) call.

	Rely on a per controller mutex to protect the bioqueues.
	Grab GEOMs topology lock when we have to and Giant when
	ISADMA needs it.  Since all access to the hardware is
	isolated in the per controller thread, the rest of the
	driver is lock & Giant free.

	Create a per-drive queue where requests are parked while
	the motor spins up.  When the motor is running the requests
	are purged to the per controller queue.  This allows
	requests to other drives to be serviced during spin-up.

	Only setup the motor-off timeout when we finish the last
	request on the queue and cancel it when a new request
	arrives.  This fixes the bug in the old code where the motor
	turned off while we were still retrying a request.

	Make the "drive-change" work reliably.  Probe the drive on
	first opens.  Probe with a recal and a seek to cyl=1 to
	reset the drive change line and check again to see if we
	have a media.

	When we see the media disappear we destroy the geom provider,
	create a new one, and flag that autodetection should happen
	next time we see a media (unless a specific format is configured).

	Add sysctl tunables for a lot of drive related parameters.
	If you spend a lot of time waiting for floppies you can
	grab the i82078 pdf from Intels web-page and try tuning
	these.

	Add sysctl debug.fdc.debugflags which will enable various
	kinds of debugging printfs.

	Add central definitions of our well known floppy formats.

	Simplify datastructures for autoselection of format and
	call the code at the right times.

	Bugfix: Remove at least one piece of code which would have
	made 2.88M floppies not work.

	Use implied seeks on enhanced controllers.

	Use multisector transfers on all controllers.  Increase
	ISADMA bounce buffers accordingly.

	Fall back to single sector when retrying.  Reset retry count
	on every successful transaction.

	Sort functions in a more sensible order and generally tidy
	up a fair bit here and there.

	Assorted related fixes and adjustments in userland utilities.

WORKAROUNDS:
	Do allow r/w opens of r/o media but refuse actual write
	operations.  This is necessary until the p4::phk_bufwork
	branch gets integrated (This problem relates to remounting
	not reopening devices, see sys/*/*/${fs}_vfsops.c for details).

	Keep PC98's private copy of the old floppy driver compiling
	and presumably working (see below).

TODO (planned)

	Move probing of drives until after interrupts/timeouts work
	(like for ATA/SCSI drives).

TODO (unplanned)

	This driver should be made to work on PC98 as well.

	Test on YE-DATA PCMCIA floppy drive.

	Fix 2.88M media.

This is a MT5 candidate (depends on the bioq_takefirst() addition).

Submitted by:	Watanabe Kazuhiro <CQG00620@nifty.ne.jp> (mostly)