On Wed, 23 May 2012 09:29:12 +0800, Liu Bo wrote:

On 05/22/2012 06:53 PM, Stefan Behrens wrote:

quoted

The device statistics are written into the device tree with each
transaction commit. Only modified statistics are written.
When a filesystem is mounted, the device statistics for each involved
device are read from the device tree and used to initialize the
counters.

Signed-off-by: Stefan Behrens <redacted>
---
 fs/btrfs/ctree.h       |   51 ++++++++++++
 fs/btrfs/disk-io.c     |    7 ++
 fs/btrfs/print-tree.c  |    3 +
 fs/btrfs/transaction.c |    4 +
 fs/btrfs/volumes.c     |  205 ++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/volumes.h     |    9 +++
 6 files changed, 279 insertions(+)

[...]

quoted

+static int update_device_stat_item(struct btrfs_trans_handle *trans,
+				   struct btrfs_root *dev_root,
+				   struct btrfs_device *device)
+{
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct extent_buffer *eb;
+	struct btrfs_device_stats_item *ptr;
+	int ret;
+
+	key.objectid = 0;
+	key.type = BTRFS_DEVICE_STATS_KEY;
+	key.offset = device->devid;
+
+	path = btrfs_alloc_path();
+	BUG_ON(!path);
+	ret = btrfs_search_slot(trans, dev_root, &key, path, 0, 1);

Since we may delete this item, I prefer cow: -1,

btrfs_search_slot(trans, dev_root, &key, path, 0, -1);

thanks,
liubo

I am sure you mean to set ins_len (the 5th parameter) to -1 and you are
right. Thanks for this finding! I will send a v5.

quoted

+	if (ret < 0) {
+		printk(KERN_WARNING "btrfs: error %d while searching for device_stats item for device %s!\n",
+		       ret, device->name);
+		goto out;
+	}
+
+	if (ret == 0 &&
+	    btrfs_item_size_nr(path->nodes[0], path->slots[0]) < sizeof(*ptr)) {
+		/* need to delete old one and insert a new one */
+		ret = btrfs_del_item(trans, dev_root, path);
+		if (ret != 0) {
+			printk(KERN_WARNING "btrfs: delete too small device_stats item for device %s failed %d!\n",
+			       device->name, ret);
+			goto out;
+		}
+		ret = 1;
+	}
+
+	if (ret == 1) {
+		/* need to insert a new item */
+		btrfs_release_path(path);
+		ret = btrfs_insert_empty_item(trans, dev_root, path,
+					      &key, sizeof(*ptr));
+		if (ret < 0) {
+			printk(KERN_WARNING "btrfs: insert device_stats item for device %s failed %d!\n",
+			       device->name, ret);
+			goto out;
+		}
+	}
+
+	eb = path->nodes[0];
+	ptr = btrfs_item_ptr(eb, path->slots[0],
+			     struct btrfs_device_stats_item);
+	btrfs_set_device_stats_cnt_write_io_errs(eb, ptr,
+		btrfs_device_stat_read(&device->cnt_write_io_errs));
+	btrfs_set_device_stats_cnt_read_io_errs(eb, ptr,
+		btrfs_device_stat_read(&device->cnt_read_io_errs));
+	btrfs_set_device_stats_cnt_flush_io_errs(eb, ptr,
+		btrfs_device_stat_read(&device->cnt_flush_io_errs));
+	btrfs_set_device_stats_cnt_corruption_errs(eb, ptr,
+		btrfs_device_stat_read(&device->cnt_corruption_errs));
+	btrfs_set_device_stats_cnt_generation_errs(eb, ptr,
+		btrfs_device_stat_read(&device->cnt_generation_errs));
+	btrfs_mark_buffer_dirty(eb);
+
+out:
+	btrfs_free_path(path);
+	return ret;
+}

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