![David Howells](/assets/img/avatar_default.png)
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>
73 lines
1.9 KiB
Text
73 lines
1.9 KiB
Text
if BLOCK
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menu "IO Schedulers"
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config IOSCHED_NOOP
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bool
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default y
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---help---
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The no-op I/O scheduler is a minimal scheduler that does basic merging
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and sorting. Its main uses include non-disk based block devices like
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memory devices, and specialised software or hardware environments
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that do their own scheduling and require only minimal assistance from
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the kernel.
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config IOSCHED_AS
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tristate "Anticipatory I/O scheduler"
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default y
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---help---
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The anticipatory I/O scheduler is the default disk scheduler. It is
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generally a good choice for most environments, but is quite large and
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complex when compared to the deadline I/O scheduler, it can also be
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slower in some cases especially some database loads.
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config IOSCHED_DEADLINE
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tristate "Deadline I/O scheduler"
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default y
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---help---
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The deadline I/O scheduler is simple and compact, and is often as
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good as the anticipatory I/O scheduler, and in some database
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workloads, better. In the case of a single process performing I/O to
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a disk at any one time, its behaviour is almost identical to the
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anticipatory I/O scheduler and so is a good choice.
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config IOSCHED_CFQ
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tristate "CFQ I/O scheduler"
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default y
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---help---
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The CFQ I/O scheduler tries to distribute bandwidth equally
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among all processes in the system. It should provide a fair
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working environment, suitable for desktop systems.
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choice
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prompt "Default I/O scheduler"
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default DEFAULT_CFQ
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help
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Select the I/O scheduler which will be used by default for all
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block devices.
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config DEFAULT_AS
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bool "Anticipatory" if IOSCHED_AS=y
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config DEFAULT_DEADLINE
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bool "Deadline" if IOSCHED_DEADLINE=y
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config DEFAULT_CFQ
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bool "CFQ" if IOSCHED_CFQ=y
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config DEFAULT_NOOP
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bool "No-op"
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endchoice
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config DEFAULT_IOSCHED
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string
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default "anticipatory" if DEFAULT_AS
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default "deadline" if DEFAULT_DEADLINE
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default "cfq" if DEFAULT_CFQ
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default "noop" if DEFAULT_NOOP
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endmenu
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endif
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