Re: [PATCH 2/3 RFC] btrfs: total_devices should count replacing devices

[Wang Shilong <wangsl.fnst@cn.fujitsu.com>]

Hello Anand,

I agree we can export @total_devices to fix 'btrfs file show' problem.
This patch addressed two problem, it is better to split it into two patches.

Could you please resend the patch, at least we should fix 'btrfs file show'
problem firstly.

Thanks,
Wang

On 03/07/2014 11:48 PM, Anand Jain wrote:
> ioctl(BTRFS_IOC_FS_INFO) returns num_devices which does not
> count seed device. num_devices is used to calculate
> the number of slots during the ioctl(BTRFS_IOC_DEV_INFO)
> but ioctl(BTRFS_IOC_DEV_INFO) would count seed devices as well.
> Due to this miss match btrfs_progs get_fs_info() hits the bug..
>              get_fs_info()
>              ::
>                      BUG_ON(ndevs >= fi_args->num_devices);
>
> what I notice is total_devices should be returned by the
> ioctl(BTRFS_IOC_FS_INFO)), however total_devices does not
> count (transient) replacing device but num_devices does.
>
> first, num_devices which appears to be a subset of
> total_devices helps to count the number of devices
> under a FSID which excludes the seed devices but
> includes the transient replacing device.
>
> total_devices which includes seed devices is as of
> now does not count the tansient replacing device,
> which IMO is a bug or the implementation details
> are not clear enough to state the role of num_devices
> and total_devices.
>
> The user land on the otherhand would want to know
> all the devices that would come out of probe
> against a FSID
>
> As of now in this patch I am making the ioctl.c local
> changes (instead of asking replace thread to update
> total_devices) to  include replacing device.
>
> Signed-off-by: Anand Jain <Anand.Jain@oracle.com>
> ---
>   fs/btrfs/ioctl.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 5036f9d..ec7d5c6 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2510,6 +2510,7 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
>   	struct btrfs_device *next;
>   	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
>   	int ret = 0;
> +	int dev_replace_running = 0;
>   
>   	if (!capable(CAP_SYS_ADMIN))
>   		return -EPERM;
> @@ -2518,8 +2519,18 @@ static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
>   	if (!fi_args)
>   		return -ENOMEM;
>   
> +	btrfs_dev_replace_lock(&root->fs_info->dev_replace);
> +	if (btrfs_dev_replace_is_ongoing(&root->fs_info->dev_replace))
> +		dev_replace_running = 1;
> +
> +	btrfs_dev_replace_unlock(&root->fs_info->dev_replace);
> +
>   	mutex_lock(&fs_devices->device_list_mutex);
> -	fi_args->num_devices = fs_devices->num_devices;
> +	if (dev_replace_running)
> +		fi_args->num_devices = fs_devices->total_devices + 1;
> +	else
> +		fi_args->num_devices = fs_devices->total_devices;
> +
>   	memcpy(&fi_args->fsid, root->fs_info->fsid, sizeof(fi_args->fsid));
>   
>   	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {