Re: [PATCH] btrfs: resize: Allow user to shrink missing device

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

On 18/11/19 3:05 PM, Qu Wenruo wrote:
> One user reported an use case where one device can't be replaced due to
> tiny device size difference.
> 
> Since it's a RAID10 fs, if we go regular "remove missing" it can take a
> long time and even not be possible due to lack of space.
> 
> So here we work around this situation by allowing user to shrink missing
> device.
> Then user can go shrink the device first, then replace it.


  Why not introduce --resize option in the replace command.
  Which shall allow replace command to resize the source-device
  to the size of the replace target-device.

Thanks, Anand

> Reported-by: Nathan Dehnel <ncdehnel@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/ioctl.c | 29 +++++++++++++++++++++++++----
>   1 file changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index de730e56d3f5..ebd2f40aca6f 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1604,6 +1604,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>   	char *sizestr;
>   	char *retptr;
>   	char *devstr = NULL;
> +	bool missing;
>   	int ret = 0;
>   	int mod = 0;
>   
> @@ -1651,7 +1652,10 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>   		goto out_free;
>   	}
>   
> -	if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
> +
> +	missing = test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
> +	if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
> +	    !missing) {
>   		btrfs_info(fs_info,
>   			   "resizer unable to apply on readonly device %llu",
>   		       devid);
> @@ -1659,13 +1663,24 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>   		goto out_free;
>   	}
>   
> -	if (!strcmp(sizestr, "max"))
> +	if (!strcmp(sizestr, "max")) {
> +		if (missing) {
> +			btrfs_info(fs_info,
> +				"'max' can't be used for missing device %llu",
> +				   devid);
> +			ret = -EPERM;
> +			goto out_free;
> +		}
>   		new_size = device->bdev->bd_inode->i_size;
> -	else {
> +	} else {
>   		if (sizestr[0] == '-') {
>   			mod = -1;
>   			sizestr++;
>   		} else if (sizestr[0] == '+') {
> +			if (missing)
> +				btrfs_info(fs_info,
> +				"'+size' can't be used for missing device %llu",
> +					   devid);
>   			mod = 1;
>   			sizestr++;
>   		}
> @@ -1694,6 +1709,12 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>   			ret = -ERANGE;
>   			goto out_free;
>   		}
> +		if (missing) {
> +			ret = -EINVAL;
> +			btrfs_info(fs_info,
> +			"can not increase device size for missing device %llu",
> +				   devid);
> +		}
>   		new_size = old_size + new_size;
>   	}
>   
> @@ -1701,7 +1722,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>   		ret = -EINVAL;
>   		goto out_free;
>   	}
> -	if (new_size > device->bdev->bd_inode->i_size) {
> +	if (!missing && new_size > device->bdev->bd_inode->i_size) {
>   		ret = -EFBIG;
>   		goto out_free;
>   	}
>