[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>

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)
+#else
+# define sector_div(n, b)( \
+{ \
+	int _res; \
+	_res = (n) % (b); \
+	(n) /= (b); \
+	_res; \
+} \
+)
+#endif
+
+#ifdef CONFIG_BLOCK
+
 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)
-#else
-# define sector_div(n, b)( \
-{ \
-	int _res; \
-	_res = (n) % (b); \
-	(n) /= (b); \
-	_res; \
-} \
-)
-#endif 
-
 #define MODULE_ALIAS_BLOCKDEV(major,minor) \
 	MODULE_ALIAS("block-major-" __stringify(major) "-" __stringify(minor))
 #define MODULE_ALIAS_BLOCKDEV_MAJOR(major) \
 	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 */
+
 #endif

include/linux/buffer_head.h

@@ -14,6 +14,8 @@
 #include <linux/wait.h>
 #include <asm/atomic.h>
 
+#ifdef CONFIG_BLOCK
+
 enum bh_state_bits {
 	BH_Uptodate,	/* Contains valid data */
 	BH_Dirty,	/* Is dirty */
@@ -301,4 +303,18 @@ static inline void lock_buffer(struct buffer_head *bh)
 }
 
 extern int __set_page_dirty_buffers(struct page *page);
+
+#else /* CONFIG_BLOCK */
+
+static inline void buffer_init(void) {}
+static inline int try_to_free_buffers(struct page *page) { return 1; }
+static inline int sync_blockdev(struct block_device *bdev) { return 0; }
+static inline int inode_has_buffers(struct inode *inode) { return 0; }
+static inline void invalidate_inode_buffers(struct inode *inode) {}
+static inline int remove_inode_buffers(struct inode *inode) { return 1; }
+static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
+static inline void invalidate_bdev(struct block_device *bdev, int destroy_dirty_buffers) {}
+
+
+#endif /* CONFIG_BLOCK */
 #endif /* _LINUX_BUFFER_HEAD_H */

include/linux/compat_ioctl.h

@@ -90,6 +90,7 @@ COMPATIBLE_IOCTL(FDTWADDLE)
 COMPATIBLE_IOCTL(FDFMTTRK)
 COMPATIBLE_IOCTL(FDRAWCMD)
 /* 0x12 */
+#ifdef CONFIG_BLOCK
 COMPATIBLE_IOCTL(BLKRASET)
 COMPATIBLE_IOCTL(BLKROSET)
 COMPATIBLE_IOCTL(BLKROGET)
@@ -103,6 +104,7 @@ COMPATIBLE_IOCTL(BLKTRACESETUP)
 COMPATIBLE_IOCTL(BLKTRACETEARDOWN)
 ULONG_IOCTL(BLKRASET)
 ULONG_IOCTL(BLKFRASET)
+#endif
 /* RAID */
 COMPATIBLE_IOCTL(RAID_VERSION)
 COMPATIBLE_IOCTL(GET_ARRAY_INFO)

include/linux/elevator.h

@@ -3,6 +3,8 @@
 
 #include <linux/percpu.h>
 
+#ifdef CONFIG_BLOCK
+
 typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
 				 struct bio *);
 
@@ -203,4 +205,5 @@ enum {
 	__val;							\
 })
 
+#endif /* CONFIG_BLOCK */
 #endif

include/linux/fs.h

@@ -1482,6 +1482,7 @@ extern void __init vfs_caches_init(unsigned long);
 extern void putname(const char *name);
 #endif
 
+#ifdef CONFIG_BLOCK
 extern int register_blkdev(unsigned int, const char *);
 extern int unregister_blkdev(unsigned int, const char *);
 extern struct block_device *bdget(dev_t);
@@ -1490,11 +1491,15 @@ extern void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
 extern struct block_device *open_by_devnum(dev_t, unsigned);
 extern struct block_device *open_partition_by_devnum(dev_t, unsigned);
-extern const struct file_operations def_blk_fops;
 extern const struct address_space_operations def_blk_aops;
+#else
+static inline void bd_forget(struct inode *inode) {}
+#endif
+extern const struct file_operations def_blk_fops;
 extern const struct file_operations def_chr_fops;
 extern const struct file_operations bad_sock_fops;
 extern const struct file_operations def_fifo_fops;
+#ifdef CONFIG_BLOCK
 extern int ioctl_by_bdev(struct block_device *, unsigned, unsigned long);
 extern int blkdev_ioctl(struct inode *, struct file *, unsigned, unsigned long);
 extern long compat_blkdev_ioctl(struct file *, unsigned, unsigned long);
@@ -1510,6 +1515,7 @@ extern void bd_release_from_disk(struct block_device *, struct gendisk *);
 #define bd_claim_by_disk(bdev, holder, disk)	bd_claim(bdev, holder)
 #define bd_release_from_disk(bdev, disk)	bd_release(bdev)
 #endif
+#endif
 
 /* fs/char_dev.c */
 #define CHRDEV_MAJOR_HASH_SIZE	255
@@ -1523,14 +1529,19 @@ extern int chrdev_open(struct inode *, struct file *);
 extern void chrdev_show(struct seq_file *,off_t);
 
 /* fs/block_dev.c */
-#define BLKDEV_MAJOR_HASH_SIZE	255
 #define BDEVNAME_SIZE	32	/* Largest string for a blockdev identifier */
+
+#ifdef CONFIG_BLOCK
+#define BLKDEV_MAJOR_HASH_SIZE	255
 extern const char *__bdevname(dev_t, char *buffer);
 extern const char *bdevname(struct block_device *bdev, char *buffer);
 extern struct block_device *lookup_bdev(const char *);
 extern struct block_device *open_bdev_excl(const char *, int, void *);
 extern void close_bdev_excl(struct block_device *);
 extern void blkdev_show(struct seq_file *,off_t);
+#else
+#define BLKDEV_MAJOR_HASH_SIZE	0
+#endif
 
 extern void init_special_inode(struct inode *, umode_t, dev_t);
 
@@ -1544,6 +1555,7 @@ extern const struct file_operations rdwr_fifo_fops;
 
 extern int fs_may_remount_ro(struct super_block *);
 
+#ifdef CONFIG_BLOCK
 /*
  * return READ, READA, or WRITE
  */
@@ -1555,9 +1567,10 @@ extern int fs_may_remount_ro(struct super_block *);
 #define bio_data_dir(bio)	((bio)->bi_rw & 1)
 
 extern int check_disk_change(struct block_device *);
-extern int invalidate_inodes(struct super_block *);
 extern int __invalidate_device(struct block_device *);
 extern int invalidate_partition(struct gendisk *, int);
+#endif
+extern int invalidate_inodes(struct super_block *);
 unsigned long invalidate_mapping_pages(struct address_space *mapping,
 					pgoff_t start, pgoff_t end);
 unsigned long invalidate_inode_pages(struct address_space *mapping);
@@ -1590,7 +1603,9 @@ extern void emergency_sync(void);
 extern void emergency_remount(void);
 extern int do_remount_sb(struct super_block *sb, int flags,
 			 void *data, int force);
+#ifdef CONFIG_BLOCK
 extern sector_t bmap(struct inode *, sector_t);
+#endif
 extern int notify_change(struct dentry *, struct iattr *);
 extern int permission(struct inode *, int, struct nameidata *);
 extern int generic_permission(struct inode *, int,
@@ -1673,9 +1688,11 @@ static inline void insert_inode_hash(struct inode *inode) {
 extern struct file * get_empty_filp(void);
 extern void file_move(struct file *f, struct list_head *list);
 extern void file_kill(struct file *f);
+#ifdef CONFIG_BLOCK
 struct bio;
 extern void submit_bio(int, struct bio *);
 extern int bdev_read_only(struct block_device *);
+#endif
 extern int set_blocksize(struct block_device *, int);
 extern int sb_set_blocksize(struct super_block *, int);
 extern int sb_min_blocksize(struct super_block *, int);
@@ -1756,6 +1773,7 @@ static inline void do_generic_file_read(struct file * filp, loff_t *ppos,
 				actor);
 }
 
+#ifdef CONFIG_BLOCK
 ssize_t __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	struct block_device *bdev, const struct iovec *iov, loff_t offset,
 	unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
@@ -1793,6 +1811,7 @@ static inline ssize_t blockdev_direct_IO_own_locking(int rw, struct kiocb *iocb,
 	return __blockdev_direct_IO(rw, iocb, inode, bdev, iov, offset,
 				nr_segs, get_block, end_io, DIO_OWN_LOCKING);
 }
+#endif
 
 extern const struct file_operations generic_ro_fops;
 

include/linux/genhd.h

@@ -11,6 +11,8 @@
 
 #include <linux/types.h>
 
+#ifdef CONFIG_BLOCK
+
 enum {
 /* These three have identical behaviour; use the second one if DOS FDISK gets
    confused about extended/logical partitions starting past cylinder 1023. */
@@ -420,3 +422,5 @@ static inline struct block_device *bdget_disk(struct gendisk *disk, int index)
 #endif
 
 #endif
+
+#endif

include/linux/mpage.h

@@ -9,6 +9,7 @@
  * (And no, it doesn't do the #ifdef __MPAGE_H thing, and it doesn't do
  * nested includes.  Get it right in the .c file).
  */
+#ifdef CONFIG_BLOCK
 
 struct writeback_control;
 typedef int (writepage_t)(struct page *page, struct writeback_control *wbc);
@@ -20,3 +21,5 @@ int mpage_writepages(struct address_space *mapping,
 		struct writeback_control *wbc, get_block_t get_block);
 int mpage_writepage(struct page *page, get_block_t *get_block,
 		struct writeback_control *wbc);
+
+#endif

include/linux/raid/md.h

@@ -53,6 +53,8 @@
 #include <linux/raid/md_u.h>
 #include <linux/raid/md_k.h>
 
+#ifdef CONFIG_MD
+
 /*
  * Different major versions are not compatible.
  * Different minor versions are only downward compatible.
@@ -95,5 +97,6 @@ extern void md_new_event(mddev_t *mddev);
 
 extern void md_update_sb(mddev_t * mddev);
 
+#endif /* CONFIG_MD */
 #endif 
 

include/linux/raid/md_k.h

@@ -18,6 +18,8 @@
 /* and dm-bio-list.h is not under include/linux because.... ??? */
 #include "../../../drivers/md/dm-bio-list.h"
 
+#ifdef CONFIG_BLOCK
+
 #define	LEVEL_MULTIPATH		(-4)
 #define	LEVEL_LINEAR		(-1)
 #define	LEVEL_FAULTY		(-5)
@@ -362,5 +364,6 @@ static inline void safe_put_page(struct page *p)
 	if (p) put_page(p);
 }
 
+#endif /* CONFIG_BLOCK */
 #endif