Revert "pktcdvd: remove driver."

This reverts commit f40eb99.

There are apparently still users out there of this driver. While we'd
love to remove it to ease the maintenance burden, let's reinstate it
for now until better (userspace) solutions can be developed.

Link: https://lore.kernel.org/lkml/20230104190115.ceglfefco475ev6c@pali/
Reported-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Documentation/ABI/testing/debugfs-pktcdvd

@@ -0,0 +1,18 @@
+What:           /sys/kernel/debug/pktcdvd/pktcdvd[0-7]
+Date:           Oct. 2006
+KernelVersion:  2.6.20
+Contact:        Thomas Maier <balagi@justmail.de>
+Description:
+
+The pktcdvd module (packet writing driver) creates
+these files in debugfs:
+
+/sys/kernel/debug/pktcdvd/pktcdvd[0-7]/
+
+    ====            ====== ====================================
+    info            0444   Lots of driver statistics and infos.
+    ====            ====== ====================================
+
+Example::
+
+    cat /sys/kernel/debug/pktcdvd/pktcdvd0/info

Documentation/ABI/testing/sysfs-class-pktcdvd

@@ -0,0 +1,97 @@
+sysfs interface
+---------------
+The pktcdvd module (packet writing driver) creates the following files in the
+sysfs: (<devid> is in the format major:minor)
+
+What:		/sys/class/pktcdvd/add
+What:		/sys/class/pktcdvd/remove
+What:		/sys/class/pktcdvd/device_map
+Date:		Oct. 2006
+KernelVersion:	2.6.20
+Contact:	Thomas Maier <balagi@justmail.de>
+Description:
+
+		==========	==============================================
+		add		(WO) Write a block device id (major:minor) to
+				create a new pktcdvd device and map it to the
+				block device.
+
+		remove		(WO) Write the pktcdvd device id (major:minor)
+				to remove the pktcdvd device.
+
+		device_map	(RO) Shows the device mapping in format:
+				pktcdvd[0-7] <pktdevid> <blkdevid>
+		==========	==============================================
+
+
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/dev
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/uevent
+Date:		Oct. 2006
+KernelVersion:	2.6.20
+Contact:	Thomas Maier <balagi@justmail.de>
+Description:
+		dev:	(RO) Device id
+
+		uevent:	(WO) To send a uevent
+
+
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/packets_started
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/packets_finished
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/kb_written
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/kb_read
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/kb_read_gather
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/stat/reset
+Date:		Oct. 2006
+KernelVersion:	2.6.20
+Contact:	Thomas Maier <balagi@justmail.de>
+Description:
+		packets_started:	(RO) Number of started packets.
+
+		packets_finished:	(RO) Number of finished packets.
+
+		kb_written:		(RO) kBytes written.
+
+		kb_read:		(RO) kBytes read.
+
+		kb_read_gather:		(RO) kBytes read to fill write packets.
+
+		reset:			(WO) Write any value to it to reset
+					pktcdvd device statistic values, like
+					bytes read/written.
+
+
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/write_queue/size
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/write_queue/congestion_off
+What:		/sys/class/pktcdvd/pktcdvd[0-7]/write_queue/congestion_on
+Date:		Oct. 2006
+KernelVersion:	2.6.20
+Contact:	Thomas Maier <balagi@justmail.de>
+Description:
+		==============	================================================
+		size		(RO) Contains the size of the bio write queue.
+
+		congestion_off	(RW) If bio write queue size is below this mark,
+				accept new bio requests from the block layer.
+
+		congestion_on	(RW) If bio write queue size is higher as this
+				mark, do no longer accept bio write requests
+				from the block layer and wait till the pktcdvd
+				device has processed enough bio's so that bio
+				write queue size is below congestion off mark.
+				A value of <= 0 disables congestion control.
+		==============	================================================
+
+
+Example:
+--------
+To use the pktcdvd sysfs interface directly, you can do::
+
+    # create a new pktcdvd device mapped to /dev/hdc
+    echo "22:0" >/sys/class/pktcdvd/add
+    cat /sys/class/pktcdvd/device_map
+    # assuming device pktcdvd0 was created, look at stat's
+    cat /sys/class/pktcdvd/pktcdvd0/stat/kb_written
+    # print the device id of the mapped block device
+    fgrep pktcdvd0 /sys/class/pktcdvd/device_map
+    # remove device, using pktcdvd0 device id   253:0
+    echo "253:0" >/sys/class/pktcdvd/remove

MAINTAINERS

@@ -16520,6 +16520,13 @@ S:	Supported
 F:	Documentation/devicetree/bindings/input/pine64,pinephone-keyboard.yaml
 F:	drivers/input/keyboard/pinephone-keyboard.c
 
+PKTCDVD DRIVER
+M:	linux-block@vger.kernel.org
+S:	Orphan
+F:	drivers/block/pktcdvd.c
+F:	include/linux/pktcdvd.h
+F:	include/uapi/linux/pktcdvd.h
+
 PLANTOWER PMS7003 AIR POLLUTION SENSOR DRIVER
 M:	Tomasz Duszynski <tduszyns@gmail.com>
 S:	Maintained

drivers/block/Kconfig

@@ -285,6 +285,49 @@ config BLK_DEV_RAM_SIZE
 	  The default value is 4096 kilobytes. Only change this if you know
 	  what you are doing.
 
+config CDROM_PKTCDVD
+	tristate "Packet writing on CD/DVD media (DEPRECATED)"
+	depends on !UML
+	depends on SCSI
+	select CDROM
+	help
+	  Note: This driver is deprecated and will be removed from the
+	  kernel in the near future!
+
+	  If you have a CDROM/DVD drive that supports packet writing, say
+	  Y to include support. It should work with any MMC/Mt Fuji
+	  compliant ATAPI or SCSI drive, which is just about any newer
+	  DVD/CD writer.
+
+	  Currently only writing to CD-RW, DVD-RW, DVD+RW and DVDRAM discs
+	  is possible.
+	  DVD-RW disks must be in restricted overwrite mode.
+
+	  See the file <file:Documentation/cdrom/packet-writing.rst>
+	  for further information on the use of this driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called pktcdvd.
+
+config CDROM_PKTCDVD_BUFFERS
+	int "Free buffers for data gathering"
+	depends on CDROM_PKTCDVD
+	default "8"
+	help
+	  This controls the maximum number of active concurrent packets. More
+	  concurrent packets can increase write performance, but also require
+	  more memory. Each concurrent packet will require approximately 64Kb
+	  of non-swappable kernel memory, memory which will be allocated when
+	  a disc is opened for writing.
+
+config CDROM_PKTCDVD_WCACHE
+	bool "Enable write caching"
+	depends on CDROM_PKTCDVD
+	help
+	  If enabled, write caching will be set for the CD-R/W device. For now
+	  this option is dangerous unless the CD-RW media is known good, as we
+	  don't do deferred write error handling yet.
+
 config ATA_OVER_ETH
 	tristate "ATA over Ethernet support"
 	depends on NET

drivers/block/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_AMIGA_Z2RAM)	+= z2ram.o
 obj-$(CONFIG_N64CART)		+= n64cart.o
 obj-$(CONFIG_BLK_DEV_RAM)	+= brd.o
 obj-$(CONFIG_BLK_DEV_LOOP)	+= loop.o
+obj-$(CONFIG_CDROM_PKTCDVD)	+= pktcdvd.o
 obj-$(CONFIG_SUNVDC)		+= sunvdc.o
 
 obj-$(CONFIG_BLK_DEV_NBD)	+= nbd.o