[PATCH] BLOCK: Make it possible to disable the block layer [try torva…

…lds#6]

Make it possible to disable the block layer.  Not all embedded devices require
it, some can make do with just JFFS2, NFS, ramfs, etc - none of which require
the block layer to be present.

This patch does the following:

 (*) Introduces CONFIG_BLOCK to disable the block layer, buffering and blockdev
     support.

 (*) Adds dependencies on CONFIG_BLOCK to any configuration item that controls
     an item that uses the block layer.  This includes:

     (*) Block I/O tracing.

     (*) Disk partition code.

     (*) All filesystems that are block based, eg: Ext3, ReiserFS, ISOFS.

     (*) The SCSI layer.  As far as I can tell, even SCSI chardevs use the
     	 block layer to do scheduling.  Some drivers that use SCSI facilities -
     	 such as USB storage - end up disabled indirectly from this.

     (*) Various block-based device drivers, such as IDE and the old CDROM
     	 drivers.

     (*) MTD blockdev handling and FTL.

     (*) JFFS - which uses set_bdev_super(), something it could avoid doing by
     	 taking a leaf out of JFFS2's book.

 (*) Makes most of the contents of linux/blkdev.h, linux/buffer_head.h and
     linux/elevator.h contingent on CONFIG_BLOCK being set.  sector_div() is,
     however, still used in places, and so is still available.

 (*) Also made contingent are the contents of linux/mpage.h, linux/genhd.h and
     parts of linux/fs.h.

 (*) Makes a number of files in fs/ contingent on CONFIG_BLOCK.

 (*) Makes mm/bounce.c (bounce buffering) contingent on CONFIG_BLOCK.

 (*) set_page_dirty() doesn't call __set_page_dirty_buffers() if CONFIG_BLOCK
     is not enabled.

 (*) fs/no-block.c is created to hold out-of-line stubs and things that are
     required when CONFIG_BLOCK is not set:

     (*) Default blockdev file operations (to give error ENODEV on opening).

 (*) Makes some /proc changes:

     (*) /proc/devices does not list any blockdevs.

     (*) /proc/diskstats and /proc/partitions are contingent on CONFIG_BLOCK.

 (*) Makes some compat ioctl handling contingent on CONFIG_BLOCK.

 (*) If CONFIG_BLOCK is not defined, makes sys_quotactl() return -ENODEV if
     given command other than Q_SYNC or if a special device is specified.

 (*) In init/do_mounts.c, no reference is made to the blockdev routines if
     CONFIG_BLOCK is not defined.  This does not prohibit NFS roots or JFFS2.

 (*) The bdflush, ioprio_set and ioprio_get syscalls can now be absent (return
     error ENOSYS by way of cond_syscall if so).

 (*) The seclvl_bd_claim() and seclvl_bd_release() security calls do nothing if
     CONFIG_BLOCK is not set, since they can't then happen.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/Kconfig

@@ -1,6 +1,24 @@
 #
 # Block layer core configuration
 #
+config BLOCK
+       bool "Enable the block layer"
+       default y
+       help
+	 This permits the block layer to be removed from the kernel if it's not
+	 needed (on some embedded devices for example).  If this option is
+	 disabled, then blockdev files will become unusable and some
+	 filesystems (such as ext3) will become unavailable.
+
+	 This option will also disable SCSI character devices and USB storage
+	 since they make use of various block layer definitions and
+	 facilities.
+
+	 Say Y here unless you know you really don't want to mount disks and
+	 suchlike.
+
+if BLOCK
+
 #XXX - it makes sense to enable this only for 32-bit subarch's, not for x86_64
 #for instance.
 config LBD
@@ -33,4 +51,6 @@ config LSF
 
 	  If unsure, say Y.
 
+endif
+
 source block/Kconfig.iosched

block/Kconfig.iosched

@@ -1,3 +1,4 @@
+if BLOCK
 
 menu "IO Schedulers"
 
@@ -67,3 +68,5 @@ config DEFAULT_IOSCHED
 	default "noop" if DEFAULT_NOOP
 
 endmenu
+
+endif

block/Makefile

@@ -2,7 +2,7 @@
 # Makefile for the kernel block layer
 #
 
-obj-y	:= elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o
+obj-$(CONFIG_BLOCK) := elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o
 
 obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o
 obj-$(CONFIG_IOSCHED_AS)	+= as-iosched.o

drivers/block/Kconfig

@@ -2,6 +2,8 @@
 # Block device driver configuration
 #
 
+if BLOCK
+
 menu "Block devices"
 
 config BLK_DEV_FD
@@ -468,3 +470,5 @@ config ATA_OVER_ETH
 	devices like the Coraid EtherDrive (R) Storage Blade.
 
 endmenu
+
+endif

drivers/cdrom/Kconfig

@@ -3,7 +3,7 @@
 #
 
 menu "Old CD-ROM drivers (not SCSI, not IDE)"
-	depends on ISA
+	depends on ISA && BLOCK
 
 config CD_NO_IDESCSI
 	bool "Support non-SCSI/IDE/ATAPI CDROM drives"

drivers/char/Kconfig

@@ -1006,6 +1006,7 @@ config GPIO_VR41XX
 
 config RAW_DRIVER
 	tristate "RAW driver (/dev/raw/rawN) (OBSOLETE)"
+	depends on BLOCK
 	help
 	  The raw driver permits block devices to be bound to /dev/raw/rawN. 
 	  Once bound, I/O against /dev/raw/rawN uses efficient zero-copy I/O. 

drivers/char/random.c

@@ -655,6 +655,7 @@ void add_interrupt_randomness(int irq)
 	add_timer_randomness(irq_timer_state[irq], 0x100 + irq);
 }
 
+#ifdef CONFIG_BLOCK
 void add_disk_randomness(struct gendisk *disk)
 {
 	if (!disk || !disk->random)
@@ -667,6 +668,7 @@ void add_disk_randomness(struct gendisk *disk)
 }
 
 EXPORT_SYMBOL(add_disk_randomness);
+#endif
 
 #define EXTRACT_SIZE 10
 
@@ -918,6 +920,7 @@ void rand_initialize_irq(int irq)
 	}
 }
 
+#ifdef CONFIG_BLOCK
 void rand_initialize_disk(struct gendisk *disk)
 {
 	struct timer_rand_state *state;
@@ -932,6 +935,7 @@ void rand_initialize_disk(struct gendisk *disk)
 		disk->random = state;
 	}
 }
+#endif
 
 static ssize_t
 random_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)

drivers/ide/Kconfig

@@ -4,6 +4,8 @@
 # Andre Hedrick <andre@linux-ide.org>
 #
 
+if BLOCK
+
 menu "ATA/ATAPI/MFM/RLL support"
 
 config IDE
@@ -1082,3 +1084,5 @@ config BLK_DEV_HD
 endif
 
 endmenu
+
+endif

drivers/md/Kconfig

@@ -2,6 +2,8 @@
 # Block device driver configuration
 #
 
+if BLOCK
+
 menu "Multi-device support (RAID and LVM)"
 
 config MD
@@ -251,3 +253,4 @@ config DM_MULTIPATH_EMC
 
 endmenu
 
+endif

drivers/message/i2o/Kconfig

@@ -88,7 +88,7 @@ config I2O_BUS
 
 config I2O_BLOCK
 	tristate "I2O Block OSM"
-	depends on I2O
+	depends on I2O && BLOCK
 	---help---
 	  Include support for the I2O Block OSM. The Block OSM presents disk
 	  and other structured block devices to the operating system. If you

drivers/mmc/Kconfig

@@ -21,7 +21,7 @@ config MMC_DEBUG
 
 config MMC_BLOCK
 	tristate "MMC block device driver"
-	depends on MMC
+	depends on MMC && BLOCK
 	default y
 	help
 	  Say Y here to enable the MMC block device driver support.

drivers/mmc/Makefile

@@ -24,7 +24,8 @@ obj-$(CONFIG_MMC_AU1X)		+= au1xmmc.o
 obj-$(CONFIG_MMC_OMAP)		+= omap.o
 obj-$(CONFIG_MMC_AT91RM9200)	+= at91_mci.o
 
-mmc_core-y := mmc.o mmc_queue.o mmc_sysfs.o
+mmc_core-y := mmc.o mmc_sysfs.o
+mmc_core-$(CONFIG_BLOCK) += mmc_queue.o
 
 ifeq ($(CONFIG_MMC_DEBUG),y)
 EXTRA_CFLAGS += -DDEBUG

drivers/mtd/Kconfig

@@ -166,7 +166,7 @@ config MTD_CHAR
 
 config MTD_BLOCK
 	tristate "Caching block device access to MTD devices"
-	depends on MTD
+	depends on MTD && BLOCK
 	---help---
 	  Although most flash chips have an erase size too large to be useful
 	  as block devices, it is possible to use MTD devices which are based
@@ -188,7 +188,7 @@ config MTD_BLOCK
 
 config MTD_BLOCK_RO
 	tristate "Readonly block device access to MTD devices"
-	depends on MTD_BLOCK!=y && MTD
+	depends on MTD_BLOCK!=y && MTD && BLOCK
 	help
 	  This allows you to mount read-only file systems (such as cramfs)
 	  from an MTD device, without the overhead (and danger) of the caching
@@ -199,7 +199,7 @@ config MTD_BLOCK_RO
 
 config FTL
 	tristate "FTL (Flash Translation Layer) support"
-	depends on MTD
+	depends on MTD && BLOCK
 	---help---
 	  This provides support for the original Flash Translation Layer which
 	  is part of the PCMCIA specification. It uses a kind of pseudo-
@@ -215,7 +215,7 @@ config FTL
 
 config NFTL
 	tristate "NFTL (NAND Flash Translation Layer) support"
-	depends on MTD
+	depends on MTD && BLOCK
 	---help---
 	  This provides support for the NAND Flash Translation Layer which is
 	  used on M-Systems' DiskOnChip devices. It uses a kind of pseudo-
@@ -238,7 +238,7 @@ config NFTL_RW
 
 config INFTL
 	tristate "INFTL (Inverse NAND Flash Translation Layer) support"
-	depends on MTD
+	depends on MTD && BLOCK
 	---help---
 	  This provides support for the Inverse NAND Flash Translation
 	  Layer which is used on M-Systems' newer DiskOnChip devices. It
@@ -255,7 +255,7 @@ config INFTL
 
 config RFD_FTL
         tristate "Resident Flash Disk (Flash Translation Layer) support"
-	depends on MTD
+	depends on MTD && BLOCK
 	---help---
 	  This provides support for the flash translation layer known
 	  as the Resident Flash Disk (RFD), as used by the Embedded BIOS

drivers/mtd/devices/Kconfig

@@ -136,7 +136,7 @@ config MTDRAM_ABS_POS
 
 config MTD_BLOCK2MTD
 	tristate "MTD using block device"
-	depends on MTD
+	depends on MTD && BLOCK
 	help
 	  This driver allows a block device to appear as an MTD. It would
 	  generally be used in the following cases:

drivers/s390/block/Kconfig

@@ -1,4 +1,4 @@
-if S390
+if S390 && BLOCK
 
 comment "S/390 block device drivers"
 	depends on S390

drivers/scsi/Kconfig

@@ -3,11 +3,13 @@ menu "SCSI device support"
 config RAID_ATTRS
 	tristate "RAID Transport Class"
 	default n
+	depends on BLOCK
 	---help---
 	  Provides RAID
 
 config SCSI
 	tristate "SCSI device support"
+	depends on BLOCK
 	---help---
 	  If you want to use a SCSI hard disk, SCSI tape drive, SCSI CD-ROM or
 	  any other SCSI device under Linux, say Y and make sure that you know