[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/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);