[PATCH] lockfs - dm bits

From: Christoph Hellwig <hch@lst.de>

This patch makes the device mapper use the new freeze_bdev/thaw_bdev
interface.  Extracted from Chris Mason's patch.

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 0270a565972760bea6293cc3655d53dc5ede4643..bdfcbe09d4d5cf96a3450a66c6df6b1b45d71ee8 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -12,6 +12,7 @@
 #include <linux/moduleparam.h>
 #include <linux/blkpg.h>
 #include <linux/bio.h>
+#include <linux/buffer_head.h>
 #include <linux/mempool.h>
 #include <linux/slab.h>
 
@@ -46,6 +47,7 @@ struct target_io {
  */
 #define DMF_BLOCK_IO 0
 #define DMF_SUSPENDED 1
+#define DMF_FS_LOCKED 2
 
 struct mapped_device {
        struct rw_semaphore lock;
@@ -80,6 +82,11 @@ struct mapped_device {
         */
        uint32_t event_nr;
        wait_queue_head_t eventq;
+
+       /*
+        * freeze/thaw support require holding onto a super block
+        */
+       struct super_block *frozen_sb;
 };
 
 #define MIN_IOS 256
@@ -884,6 +891,52 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
        return 0;
 }
 
+/*
+ * Functions to lock and unlock any filesystem running on the
+ * device.
+ */
+static int __lock_fs(struct mapped_device *md)
+{
+       struct block_device *bdev;
+
+       if (test_and_set_bit(DMF_FS_LOCKED, &md->flags))
+               return 0;
+
+       bdev = bdget_disk(md->disk, 0);
+       if (!bdev) {
+               DMWARN("bdget failed in __lock_fs");
+               return -ENOMEM;
+       }
+
+       WARN_ON(md->frozen_sb);
+       md->frozen_sb = freeze_bdev(bdev);
+       /* don't bdput right now, we don't want the bdev
+        * to go away while it is locked.  We'll bdput
+        * in __unlock_fs
+        */
+       return 0;
+}
+
+static int __unlock_fs(struct mapped_device *md)
+{
+       struct block_device *bdev;
+
+       if (!test_and_clear_bit(DMF_FS_LOCKED, &md->flags))
+               return 0;
+
+       bdev = bdget_disk(md->disk, 0);
+       if (!bdev) {
+               DMWARN("bdget failed in __unlock_fs");
+               return -ENOMEM;
+       }
+
+       thaw_bdev(bdev, md->frozen_sb);
+       md->frozen_sb = NULL;
+       bdput(bdev);
+       bdput(bdev);
+       return 0;
+}
+
 /*
  * We need to be able to change a mapping table under a mounted
  * filesystem.  For example we might want to move some data in
@@ -896,13 +949,27 @@ int dm_suspend(struct mapped_device *md)
        struct dm_table *map;
        DECLARE_WAITQUEUE(wait, current);
 
-       down_write(&md->lock);
+       /* Flush I/O to the device. */
+       down_read(&md->lock);
+       if (test_bit(DMF_BLOCK_IO, &md->flags)) {
+               up_read(&md->lock);
+               return -EINVAL;
+       }
+
+       __lock_fs(md);
+       up_read(&md->lock);
 
        /*
         * First we set the BLOCK_IO flag so no more ios will be
         * mapped.
         */
+       down_write(&md->lock);
        if (test_bit(DMF_BLOCK_IO, &md->flags)) {
+               /*
+                * If we get here we know another thread is
+                * trying to suspend as well, so we leave the fs
+                * locked for this thread.
+                */
                up_write(&md->lock);
                return -EINVAL;
        }
@@ -937,6 +1004,7 @@ int dm_suspend(struct mapped_device *md)
 
        /* were we interrupted ? */
        if (atomic_read(&md->pending)) {
+               __unlock_fs(md);
                clear_bit(DMF_BLOCK_IO, &md->flags);
                up_write(&md->lock);
                return -EINTR;
@@ -974,6 +1042,7 @@ int dm_resume(struct mapped_device *md)
        def = bio_list_get(&md->deferred);
        __flush_deferred_io(md, def);
        up_write(&md->lock);
+       __unlock_fs(md);
        dm_table_unplug_all(map);
        dm_table_put(map);