[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>

1 files changed, 10 insertions, 1 deletions

diff --git a/fs/proc/proc_misc.c b/fs/proc/proc_misc.c
index 5bbd6089605..66bc425f2f3 100644
--- a/fs/proc/proc_misc.c
+++ b/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