Re: [PATCH 2/5] vfs: create a generic checking function for FS_IOC_FSSETXATTR

[Al Viro]

On Tue, Jun 25, 2019 at 07:32:18PM -0700, Darrick J. Wong wrote:
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -373,10 +373,9 @@ static int check_xflags(unsigned int flags)
>  static int btrfs_ioctl_fsgetxattr(struct file *file, void __user *arg)
>  {
>  	struct btrfs_inode *binode = BTRFS_I(file_inode(file));
> -	struct fsxattr fa;
> -
> -	memset(&fa, 0, sizeof(fa));
> -	fa.fsx_xflags = btrfs_inode_flags_to_xflags(binode->flags);
> +	struct fsxattr fa = {
> +		.fsx_xflags = btrfs_inode_flags_to_xflags(binode->flags),
> +	};

Umm...  Sure, there's no padding, but still - you are going to copy that thing
to userland...  How about

static inline void simple_fill_fsxattr(struct fsxattr *fa, unsigned xflags)
{
	memset(fa, 0, sizeof(*fa));
	fa->fsx_xflags = xflags;
}

and let the compiler optimize the crap out?