From 9361401eb7619c033e2394e4f9f6d410d6719ac7 Mon Sep 17 00:00:00 2001 From: David Howells Date: Sat, 30 Sep 2006 20:45:40 +0200 Subject: [PATCH] BLOCK: Make it possible to disable the block layer [try #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 Signed-off-by: Jens Axboe --- block/Kconfig | 20 ++++++++++++++++++++ block/Kconfig.iosched | 3 +++ block/Makefile | 2 +- 3 files changed, 24 insertions(+), 1 deletion(-) (limited to 'block') diff --git a/block/Kconfig b/block/Kconfig index b6f5f0a7965..9af6c614dfd 100644 --- a/block/Kconfig +++ b/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 diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched index 48d090e266f..903f0d3b685 100644 --- a/block/Kconfig.iosched +++ b/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 diff --git a/block/Makefile b/block/Makefile index c05de0e0037..4b84d0d5947 100644 --- a/block/Makefile +++ b/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 -- cgit v1.2.3