[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 <dhowells@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
19 years ago
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if S390 && BLOCK
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comment "S/390 block device drivers"
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depends on S390
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config BLK_DEV_XPRAM
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tristate "XPRAM disk support"
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depends on S390
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help
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Select this option if you want to use your expanded storage on S/390
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or zSeries as a disk. This is useful as a _fast_ swap device if you
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want to access more than 2G of memory when running in 31 bit mode.
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This option is also available as a module which will be called
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xpram. If unsure, say "N".
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config DCSSBLK
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tristate "DCSSBLK support"
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help
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Support for dcss block device
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config DASD
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tristate "Support for DASD devices"
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depends on CCW
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help
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Enable this option if you want to access DASDs directly utilizing
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S/390s channel subsystem commands. This is necessary for running
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natively on a single image or an LPAR.
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config DASD_PROFILE
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bool "Profiling support for dasd devices"
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depends on DASD
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help
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Enable this option if you want to see profiling information
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in /proc/dasd/statistics.
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config DASD_ECKD
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tristate "Support for ECKD Disks"
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depends on DASD
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help
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ECKD devices are the most commonly used devices. You should enable
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this option unless you are very sure to have no ECKD device.
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config DASD_FBA
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tristate "Support for FBA Disks"
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depends on DASD
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help
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Select this option to be able to access FBA devices. It is safe to
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say "Y".
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config DASD_DIAG
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tristate "Support for DIAG access to Disks"
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depends on DASD
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help
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Select this option if you want to use Diagnose250 command to access
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Disks under VM. If you are not running under VM or unsure what it is,
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say "N".
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config DASD_EER
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bool "Extended error reporting (EER)"
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depends on DASD
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help
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This driver provides a character device interface to the
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DASD extended error reporting. This is only needed if you want to
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use applications written for the EER facility.
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endif
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