• David Howells's avatar
    [PATCH] BLOCK: Make it possible to disable the block layer [try #6] · 9361401e
    David Howells authored
    
    
    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: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    9361401e