[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>

fs/no-block.c

+/* no-block.c: implementation of routines required for non-BLOCK configuration
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+
+static int no_blkdev_open(struct inode * inode, struct file * filp)
+{
+	return -ENODEV;
+}
+
+const struct file_operations def_blk_fops = {
+	.open		= no_blkdev_open,
+};

fs/partitions/Makefile

@@ -2,7 +2,7 @@
 # Makefile for the linux kernel.
 #
 
-obj-y := check.o
+obj-$(CONFIG_BLOCK) := check.o
 
 obj-$(CONFIG_ACORN_PARTITION) += acorn.o
 obj-$(CONFIG_AMIGA_PARTITION) += amiga.o

fs/proc/proc_misc.c

@@ -277,12 +277,15 @@ static int devinfo_show(struct seq_file *f, void *v)
 		if (i == 0)
 			seq_printf(f, "Character devices:\n");
 		chrdev_show(f, i);
-	} else {
+	}
+#ifdef CONFIG_BLOCK
+	else {
 		i -= CHRDEV_MAJOR_HASH_SIZE;
 		if (i == 0)
 			seq_printf(f, "\nBlock devices:\n");
 		blkdev_show(f, i);
 	}
+#endif
 	return 0;
 }
 
@@ -355,6 +358,7 @@ static int stram_read_proc(char *page, char **start, off_t off,
 }
 #endif
 
+#ifdef CONFIG_BLOCK
 extern struct seq_operations partitions_op;
 static int partitions_open(struct inode *inode, struct file *file)
 {
@@ -378,6 +382,7 @@ static struct file_operations proc_diskstats_operations = {
 	.llseek		= seq_lseek,
 	.release	= seq_release,
 };
+#endif
 
 #ifdef CONFIG_MODULES
 extern struct seq_operations modules_op;
@@ -695,7 +700,9 @@ void __init proc_misc_init(void)
 		entry->proc_fops = &proc_kmsg_operations;
 	create_seq_entry("devices", 0, &proc_devinfo_operations);
 	create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations);
+#ifdef CONFIG_BLOCK
 	create_seq_entry("partitions", 0, &proc_partitions_operations);
+#endif
 	create_seq_entry("stat", 0, &proc_stat_operations);
 	create_seq_entry("interrupts", 0, &proc_interrupts_operations);
 #ifdef CONFIG_SLAB
@@ -707,7 +714,9 @@ void __init proc_misc_init(void)
 	create_seq_entry("buddyinfo",S_IRUGO, &fragmentation_file_operations);
 	create_seq_entry("vmstat",S_IRUGO, &proc_vmstat_file_operations);
 	create_seq_entry("zoneinfo",S_IRUGO, &proc_zoneinfo_file_operations);
+#ifdef CONFIG_BLOCK
 	create_seq_entry("diskstats", 0, &proc_diskstats_operations);
+#endif
 #ifdef CONFIG_MODULES
 	create_seq_entry("modules", 0, &proc_modules_operations);
 #endif

fs/quota.c

@@ -337,6 +337,34 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id, void
 	return 0;
 }
 
+/*
+ * look up a superblock on which quota ops will be performed
+ * - use the name of a block device to find the superblock thereon
+ */
+static inline struct super_block *quotactl_block(const char __user *special)
+{
+#ifdef CONFIG_BLOCK
+	struct block_device *bdev;
+	struct super_block *sb;
+	char *tmp = getname(special);
+
+	if (IS_ERR(tmp))
+		return ERR_PTR(PTR_ERR(tmp));
+	bdev = lookup_bdev(tmp);
+	putname(tmp);
+	if (IS_ERR(bdev))
+		return ERR_PTR(PTR_ERR(bdev));
+	sb = get_super(bdev);
+	bdput(bdev);
+	if (!sb)
+		return ERR_PTR(-ENODEV);
+
+	return sb;
+#else
+	return ERR_PTR(-ENODEV);
+#endif
+}
+
 /*
  * This is the system call interface. This communicates with
  * the user-level programs. Currently this only supports diskquota
@@ -347,25 +375,15 @@ asmlinkage long sys_quotactl(unsigned int cmd, const char __user *special, qid_t
 {
 	uint cmds, type;
 	struct super_block *sb = NULL;
-	struct block_device *bdev;
-	char *tmp;
 	int ret;
 
 	cmds = cmd >> SUBCMDSHIFT;
 	type = cmd & SUBCMDMASK;
 
 	if (cmds != Q_SYNC || special) {
-		tmp = getname(special);
-		if (IS_ERR(tmp))
-			return PTR_ERR(tmp);
-		bdev = lookup_bdev(tmp);
-		putname(tmp);
-		if (IS_ERR(bdev))
-			return PTR_ERR(bdev);
-		sb = get_super(bdev);
-		bdput(bdev);
-		if (!sb)
-			return -ENODEV;
+		sb = quotactl_block(special);
+		if (IS_ERR(sb))
+			return PTR_ERR(sb);
 	}
 
 	ret = check_quotactl_valid(sb, type, cmds, id);

fs/super.c

@@ -571,8 +571,10 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 {
 	int retval;
 	
+#ifdef CONFIG_BLOCK
 	if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
 		return -EACCES;
+#endif
 	if (flags & MS_RDONLY)
 		acct_auto_close(sb);
 	shrink_dcache_sb(sb);
@@ -692,6 +694,7 @@ void kill_litter_super(struct super_block *sb)
 
 EXPORT_SYMBOL(kill_litter_super);
 
+#ifdef CONFIG_BLOCK
 static int set_bdev_super(struct super_block *s, void *data)
 {
 	s->s_bdev = data;
@@ -787,6 +790,7 @@ void kill_block_super(struct super_block *sb)
 }
 
 EXPORT_SYMBOL(kill_block_super);
+#endif
 
 int get_sb_nodev(struct file_system_type *fs_type,
 	int flags, void *data,

fs/xfs/Kconfig

 config XFS_FS
 	tristate "XFS filesystem support"
+	depends on BLOCK
 	help
 	  XFS is a high performance journaling filesystem which originated
 	  on the SGI IRIX platform.  It is completely multi-threaded, can

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
 

include/scsi/scsi_tcq.h

@@ -6,7 +6,6 @@
 #include <scsi/scsi_device.h>
 #include <scsi/scsi_host.h>
 
-
 #define MSG_SIMPLE_TAG	0x20
 #define MSG_HEAD_TAG	0x21
 #define MSG_ORDERED_TAG	0x22
@@ -14,6 +13,7 @@
 #define SCSI_NO_TAG	(-1)    /* identify no tag in use */
 
 
+#ifdef CONFIG_BLOCK
 
 /**
  * scsi_get_tag_type - get the type of tag the device supports
@@ -144,4 +144,5 @@ static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
 	return shost->bqt ? 0 : -ENOMEM;
 }
 
+#endif /* CONFIG_BLOCK */
 #endif /* _SCSI_SCSI_TCQ_H */

init/Kconfig

@@ -92,7 +92,7 @@ config LOCALVERSION_AUTO
 
 config SWAP
 	bool "Support for paging of anonymous memory (swap)"
-	depends on MMU
+	depends on MMU && BLOCK
 	default y
 	help
 	  This option allows you to choose whether you want to have support

init/do_mounts.c

@@ -285,7 +285,11 @@ void __init mount_block_root(char *name, int flags)
 {
 	char *fs_names = __getname();
 	char *p;
+#ifdef CONFIG_BLOCK
 	char b[BDEVNAME_SIZE];
+#else
+	const char *b = name;
+#endif
 
 	get_fs_names(fs_names);
 retry:
@@ -304,7 +308,9 @@ retry:
 		 * Allow the user to distinguish between failed sys_open
 		 * and bad superblock on root device.
 		 */
+#ifdef CONFIG_BLOCK
 		__bdevname(ROOT_DEV, b);
+#endif
 		printk("VFS: Cannot open root device \"%s\" or %s\n",
 				root_device_name, b);
 		printk("Please append a correct \"root=\" boot option\n");
@@ -316,7 +322,10 @@ retry:
 	for (p = fs_names; *p; p += strlen(p)+1)
 		printk(" %s", p);
 	printk("\n");
-	panic("VFS: Unable to mount root fs on %s", __bdevname(ROOT_DEV, b));
+#ifdef CONFIG_BLOCK
+	__bdevname(ROOT_DEV, b);
+#endif
+	panic("VFS: Unable to mount root fs on %s", b);
 out:
 	putname(fs_names);
 }
@@ -387,8 +396,10 @@ void __init mount_root(void)
 			change_floppy("root floppy");
 	}
 #endif
+#ifdef CONFIG_BLOCK
 	create_dev("/dev/root", ROOT_DEV);
 	mount_block_root("/dev/root", root_mountflags);
+#endif
 }
 
 /*

kernel/sys_ni.c

@@ -134,3 +134,8 @@ cond_syscall(sys_madvise);
 cond_syscall(sys_mremap);
 cond_syscall(sys_remap_file_pages);
 cond_syscall(compat_sys_move_pages);
+
+/* block-layer dependent */
+cond_syscall(sys_bdflush);
+cond_syscall(sys_ioprio_set);
+cond_syscall(sys_ioprio_get);

mm/Makefile

@@ -12,7 +12,7 @@ obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   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