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

Darrick J. Wong
2019-06-26T15:37:18Z

On Wed, Jun 26, 2019 at 05:11:33AM +0100, Al Viro wrote:
> 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?

The v2 series used to do that, but Christoph complained that having a
helper for a two-line memset and initialization was silly[1] so now we
have this version.

I don't mind reinstating it as a static inline helper, but I'd like some
input from any of the btrfs developers (or you, Al) about which form is
preferred.

--D

[1] https://lkml.org/lkml/2019/6/25/533