Re: [PATCH] btrfs: fix GET_SUBVOL_INFO after compat refactor

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/7/13 17:20, Daan De Meyer via B4 Relay 写道:
> From: Daan De Meyer <daan@amutable.com>
> 
> btrfs_search_slot() returns a positive value when the search key does
> not exactly match an item. This is expected here, since offset 0 is used
> to find the first ROOT_BACKREF for the subvolume and the actual key has
> the parent root ID as its offset.
> 
> Before the compat ioctl refactoring, the native handler still copied the
> filled structure to userspace when the search returned 1. After the
> lookup was moved to a shared helper, both native and compat callers
> treat the positive return value as a failure and skip copy_to_user(),
> leaving BTRFS_IOC_GET_SUBVOL_INFO unusable for non-top-level
> subvolumes.
> 
> Reset ret after successfully validating and reading the ROOT_BACKREF so
> the helper reports success and both callers copy the result to
> userspace.
> 
> Fixes: 538e5bdbc899 ("btrfs: add 32-bit compat ioctl for BTRFS_IOC_GET_SUBVOL_INFO")
> Signed-off-by: Daan De Meyer <daan@amutable.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu

> ---
> Fix BTRFS_IOC_GET_SUBVOL_INFO for non-top-level subvolumes after the
> recent 32-bit compat ioctl refactor.
> ---
>   fs/btrfs/ioctl.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 9d47d16394fc..ab6c17716026 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2042,6 +2042,7 @@ static int _btrfs_ioctl_get_subvol_info(struct inode *inode,
>   			ret = -ENOENT;
>   			goto out;
>   		}
> +		ret = 0;
>   	}
>   
>   out:
> 
> ---
> base-commit: cab9e339cfbc1a4e075e53e281dfb00391e1a6bb
> change-id: 20260713-btrfs-get-subvol-info-fix-e93803926554
> 
> Best regards,
> --
> Daan De Meyer <daan@amutable.com>
> 
> 
>