Re: [PATCH RFC] btrfs: Add ctime/mtime update for btrfs device add/remove.

[Anand Jain <Anand.Jain@oracle.com>]

Hi Qu,

  In line below...

On 16/04/14 17:02, Qu Wenruo wrote:
> Btrfs will send uevent to udev inform the device change,
> but ctime/mtime for the block device inode is not udpated, which cause
> libblkid used by btrfs-progs unable to detect device change and use old
> cache, causing 'btrfs dev scan; btrfs dev rmove; btrfs dev scan' give an
> error message.
>
> Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
> Cc: Karel Zak <kzak@redhat.com>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
>   fs/btrfs/volumes.c | 26 ++++++++++++++++++++++++--
>   1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 49d7fab..ce232d7 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1452,6 +1452,22 @@ out:
>   	return ret;
>   }
>
> +/*
> + * Function to update ctime/mtime for a given device path.
> + * Mainly used for ctime/mtime based probe like libblkid.
> + */
> +static void update_dev_time(char *path_name)
> +{
> +	struct file *filp;
> +
> +	filp = filp_open(path_name, O_RDWR, 0);
> +	if (!filp)
> +		return;
> +	file_update_time(filp);
> +	filp_close(filp, NULL);
> +	return;
> +}
> +

   IMO /(I might be wrong) I think its not a good idea to explicitly
   achieve this. Since this thread would have already scratched the
   device's SB, shouldn't that take care of updating the mtime ?

Thanks, Anand


>   static int btrfs_rm_dev_item(struct btrfs_root *root,
>   			     struct btrfs_device *device)
>   {
> @@ -1704,10 +1720,14 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
>
>   	ret = 0;
>
> -	/* Notify udev that device has changed */
> -	if (bdev)
> +	if (bdev) {
> +		/* Notify udev that device has changed */
>   		btrfs_kobject_uevent(bdev, KOBJ_CHANGE);
>
> +		/* Update ctime/mtime for device path for libblkid */
> +		update_dev_time(device_path);
> +	}
> +



>   error_brelse:
>   	brelse(bh);
>   	if (bdev)
> @@ -2146,6 +2166,8 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
>   		ret = btrfs_commit_transaction(trans, root);
>   	}
>
> +	/* Update ctime/mtime for libblkid */
> +	update_dev_time(device_path);
>   	return ret;
>
>   error_trans:
>