path: root/include/linux/blkdev.h
diff options
authorDavid Howells <>2006-09-30 20:45:40 +0200
committerJens Axboe <>2006-09-30 20:52:31 +0200
commit9361401eb7619c033e2394e4f9f6d410d6719ac7 (patch)
tree04b94a71f2366988c17740d1c16cfbdec41d5d2e /include/linux/blkdev.h
parentd366e40a1cabd453be6e2609caa7e12f9ca17b1f (diff)
[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 <>
Diffstat (limited to 'include/linux/blkdev.h')
1 files changed, 36 insertions, 14 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2c01a90998a7..3e36107d342a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -16,6 +16,22 @@
#include <asm/scatterlist.h>
+#ifdef CONFIG_LBD
+# include <asm/div64.h>
+# define sector_div(a, b) do_div(a, b)
+# define sector_div(n, b)( \
+{ \
+ int _res; \
+ _res = (n) % (b); \
+ (n) /= (b); \
+ _res; \
+} \
struct scsi_ioctl_command;
struct request_queue;
@@ -818,24 +834,30 @@ struct work_struct;
int kblockd_schedule_work(struct work_struct *work);
void kblockd_flush(void);
-#ifdef CONFIG_LBD
-# include <asm/div64.h>
-# define sector_div(a, b) do_div(a, b)
-# define sector_div(n, b)( \
-{ \
- int _res; \
- _res = (n) % (b); \
- (n) /= (b); \
- _res; \
-} \
#define MODULE_ALIAS_BLOCKDEV(major,minor) \
MODULE_ALIAS("block-major-" __stringify(major) "-" __stringify(minor))
MODULE_ALIAS("block-major-" __stringify(major) "-*")
+#else /* CONFIG_BLOCK */
+ * stubs for when the block layer is configured out
+ */
+#define buffer_heads_over_limit 0
+static inline long blk_congestion_wait(int rw, long timeout)
+ return timeout;
+static inline long nr_blockdev_pages(void)
+ return 0;
+static inline void exit_io_context(void) {}
+#endif /* CONFIG_BLOCK */