Add a ioctl which dumps out all of the in-use buffer heads for a block device

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index 3d3e7a4..5c428a8 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -705,6 +705,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 	switch (cmd) {
 	case HDIO_GETGEO:
 		return compat_hdio_getgeo(disk, bdev, compat_ptr(arg));
+	case BLKDUMPUSEDBUFFERS:
 	case BLKFLSBUF:
 	case BLKROSET:
 	case BLKDISCARD:
diff --git a/block/ioctl.c b/block/ioctl.c
index c832d63..9b73953 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -367,6 +367,13 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 		ret = blk_trace_ioctl(bdev, cmd, (char __user *) arg);
 		unlock_kernel();
 		break;
+	case BLKDUMPUSEDBUFFERS:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EACCES;
+		dump_used_buffers(bdev);
+		ret = 0;
+		break;
+
 	default:
 		ret = __blkdev_driver_ioctl(bdev, mode, cmd, arg);
 	}
diff --git a/fs/buffer.c b/fs/buffer.c
index 6569fda..852e7ac 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -33,6 +33,7 @@
 #include <linux/writeback.h>
 #include <linux/hash.h>
 #include <linux/suspend.h>
+#include <linux/pagevec.h>
 #include <linux/buffer_head.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/bio.h>
@@ -246,6 +247,45 @@ void thaw_bdev(struct block_device *bdev, struct super_block *sb)
 }
 EXPORT_SYMBOL(thaw_bdev);
 
+void dump_used_buffers(struct block_device *bdev)
+{
+	struct inode *bd_inode = bdev->bd_inode;
+	struct address_space *bd_mapping = bd_inode->i_mapping;
+	struct buffer_head *bh, *head;
+	struct pagevec pvec;
+	unsigned long index = 0;
+	int nr_pages, i, count, total = 0;
+	char b[BDEVNAME_SIZE];
+
+	spin_lock(&bd_mapping->private_lock);
+	printk(KERN_INFO "Begin dump of block device %s\n", bdevname(bdev, b));
+	while (1) {
+		nr_pages = pagevec_lookup(&pvec, bd_mapping, index, PAGEVEC_SIZE);
+		if (nr_pages == 0)
+			break;
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+			index = page->index + 1;
+
+			if (!page_has_buffers(page))
+				continue;
+			bh = head = page_buffers(page);
+			do {
+				count = atomic_read(&bh->b_count);
+				if (count) {
+					printk(KERN_INFO
+					       "buffer in-use: block %Lu count %d\n",
+					       (unsigned long long) bh->b_blocknr, count);
+					total++;
+				}
+				bh = bh->b_this_page;
+			} while (bh != head);
+		}
+	}
+	printk(KERN_INFO "Total number of in-use buffers: %d\n", total);
+	spin_unlock(&bd_mapping->private_lock);
+}
+
 /*
  * Various filesystems appear to want __find_get_block to be non-blocking.
  * But it's the page lock which protects the buffers.  To get around this,
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 3ce64b9..053e644 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -193,6 +193,7 @@ void write_boundary_block(struct block_device *bdev,
 			sector_t bblock, unsigned blocksize);
 int bh_uptodate_or_lock(struct buffer_head *bh);
 int bh_submit_read(struct buffer_head *bh);
+void dump_used_buffers(struct block_device *bdev);
 
 extern int buffer_heads_over_limit;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5b248d6..a08e4d0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -231,6 +231,8 @@ extern int dir_notify_enable;
 #define BLKTRACETEARDOWN _IO(0x12,118)
 #define BLKDISCARD _IO(0x12,119)
 
+#define BLKDUMPUSEDBUFFERS _IO(0x12,130)
+
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
 #define FIGETBSZ   _IO(0x00,2)	/* get the block size used for bmap */