dump-in-use-buffers

   1 Add a ioctl which dumps out all of the in-use buffer heads for a block device
   2
   3 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
   4 ---
   5  block/compat_ioctl.c |    4 ++++
   6  block/ioctl.c        |   11 +++++++++++
   7  fs/buffer.c          |   40 ++++++++++++++++++++++++++++++++++++++++
   8  3 files changed, 55 insertions(+), 0 deletions(-)
   9
  10 diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
  11 index 4eb8e9e..2535cb1 100644
  12 --- a/block/compat_ioctl.c
  13 +++ b/block/compat_ioctl.c
  14 @@ -11,6 +11,9 @@
  15  #include <linux/types.h>
  16  #include <linux/uaccess.h>
  17
  18 +/* For debugging purposes; see block/ioctl.c */
  19 +#define BLKDUMPUSEDBUFFERS _IO(0x12,130)
  20 +
  21  static int compat_put_ushort(unsigned long arg, unsigned short val)
  22  {
  23         return put_user(val, (unsigned short __user *)compat_ptr(arg));
  24 @@ -749,6 +752,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
  25                 return compat_put_int(arg, bdev_alignment_offset(bdev));
  26         case BLKDISCARDZEROES:
  27                 return compat_put_uint(arg, bdev_discard_zeroes_data(bdev));
  28 +       case BLKDUMPUSEDBUFFERS:
  29         case BLKFLSBUF:
  30         case BLKROSET:
  31         case BLKDISCARD:
  32 diff --git a/block/ioctl.c b/block/ioctl.c
  33 index be48ea5..8cc002b 100644
  34 --- a/block/ioctl.c
  35 +++ b/block/ioctl.c
  36 @@ -8,6 +8,10 @@
  37  #include <linux/blktrace_api.h>
  38  #include <asm/uaccess.h>
  39
  40 +/* For debugging purposes */
  41 +#define BLKDUMPUSEDBUFFERS _IO(0x12,130)
  42 +extern void dump_used_buffers(struct block_device *bdev);
  43 +
  44  static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user *arg)
  45  {
  46         struct block_device *bdevp;
  47 @@ -332,6 +336,13 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
  48                 ret = blk_trace_ioctl(bdev, cmd, (char __user *) arg);
  49                 unlock_kernel();
  50                 break;
  51 +       case BLKDUMPUSEDBUFFERS:
  52 +               if (!capable(CAP_SYS_ADMIN))
  53 +                       return -EACCES;
  54 +               dump_used_buffers(bdev);
  55 +               ret = 0;
  56 +               break;
  57 +
  58         default:
  59                 ret = __blkdev_driver_ioctl(bdev, mode, cmd, arg);
  60         }
  61 diff --git a/fs/buffer.c b/fs/buffer.c
  62 index 6fa5302..8438330 100644
  63 --- a/fs/buffer.c
  64 +++ b/fs/buffer.c
  65 @@ -33,6 +33,7 @@
  66  #include <linux/writeback.h>
  67  #include <linux/hash.h>
  68  #include <linux/suspend.h>
  69 +#include <linux/pagevec.h>
  70  #include <linux/buffer_head.h>
  71  #include <linux/task_io_accounting_ops.h>
  72  #include <linux/bio.h>
  73 @@ -300,6 +301,45 @@ static void free_more_memory(void)
  74         }
  75  }
  76
  77 +void dump_used_buffers(struct block_device *bdev)
  78 +{
  79 +       struct inode *bd_inode = bdev->bd_inode;
  80 +       struct address_space *bd_mapping = bd_inode->i_mapping;
  81 +       struct buffer_head *bh, *head;
  82 +       struct pagevec pvec;
  83 +       unsigned long index = 0;
  84 +       int nr_pages, i, count, total = 0;
  85 +       char b[BDEVNAME_SIZE];
  86 +
  87 +       spin_lock(&bd_mapping->private_lock);
  88 +       printk(KERN_INFO "Begin dump of block device %s\n", bdevname(bdev, b));
  89 +       while (1) {
  90 +               nr_pages = pagevec_lookup(&pvec, bd_mapping, index, PAGEVEC_SIZE);
  91 +               if (nr_pages == 0)
  92 +                       break;
  93 +               for (i = 0; i < nr_pages; i++) {
  94 +                       struct page *page = pvec.pages[i];
  95 +                       index = page->index + 1;
  96 +
  97 +                       if (!page_has_buffers(page))
  98 +                               continue;
  99 +                       bh = head = page_buffers(page);
 100 +                       do {
 101 +                               count = atomic_read(&bh->b_count);
 102 +                               if (count) {
 103 +                                       printk(KERN_INFO
 104 +                                              "buffer in-use: block %Lu count %d\n",
 105 +                                              (unsigned long long) bh->b_blocknr, count);
 106 +                                       total++;
 107 +                               }
 108 +                               bh = bh->b_this_page;
 109 +                       } while (bh != head);
 110 +               }
 111 +       }
 112 +       printk(KERN_INFO "Total number of in-use buffers: %d\n", total);
 113 +       spin_unlock(&bd_mapping->private_lock);
 114 +}
 115 +
 116  /*
 117   * I/O completion handler for block_read_full_page() - pages
 118   * which come unlocked at the end of I/O.