[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>
diff --git a/mm/Makefile b/mm/Makefile
index 4f2166a..12b3a4e 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -12,7 +12,7 @@
readahead.o swap.o truncate.o vmscan.o \
prio_tree.o util.o mmzone.o vmstat.o $(mmu-y)
-ifeq ($(CONFIG_MMU),y)
+ifeq ($(CONFIG_MMU)$(CONFIG_BLOCK),yy)
obj-y += bounce.o
endif
obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o thrash.o
diff --git a/mm/filemap.c b/mm/filemap.c
index d6846de..c4fe97f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2020,6 +2020,7 @@
if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
*count = inode->i_sb->s_maxbytes - *pos;
} else {
+#ifdef CONFIG_BLOCK
loff_t isize;
if (bdev_read_only(I_BDEV(inode)))
return -EPERM;
@@ -2031,6 +2032,9 @@
if (*pos + *count > isize)
*count = isize - *pos;
+#else
+ return -EPERM;
+#endif
}
return 0;
}
diff --git a/mm/migrate.c b/mm/migrate.c
index 7f50e3f..ba2453f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -409,6 +409,7 @@
}
EXPORT_SYMBOL(migrate_page);
+#ifdef CONFIG_BLOCK
/*
* Migration function for pages with buffers. This function can only be used
* if the underlying filesystem guarantees that no other references to "page"
@@ -466,6 +467,7 @@
return 0;
}
EXPORT_SYMBOL(buffer_migrate_page);
+#endif
/*
* Writeback a page to clean the dirty state
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ecf2783..c0d4ce1 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -807,9 +807,11 @@
if (likely(mapping)) {
int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
- if (spd)
- return (*spd)(page);
- return __set_page_dirty_buffers(page);
+#ifdef CONFIG_BLOCK
+ if (!spd)
+ spd = __set_page_dirty_buffers;
+#endif
+ return (*spd)(page);
}
if (!PageDirty(page)) {
if (!TestSetPageDirty(page))
diff --git a/mm/truncate.c b/mm/truncate.c
index cd3e34b..8fde658 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -35,8 +35,10 @@
{
void (*invalidatepage)(struct page *, unsigned long);
invalidatepage = page->mapping->a_ops->invalidatepage;
+#ifdef CONFIG_BLOCK
if (!invalidatepage)
invalidatepage = block_invalidatepage;
+#endif
if (invalidatepage)
(*invalidatepage)(page, offset);
}