On Wed, Feb 07, 2024 at 09:01:05AM +1100, Dave Chinner wrote:
> On Tue, Feb 06, 2024 at 03:18:51PM -0500, Kent Overstreet wrote:
> > +static int ioctl_getfsuuid(struct file *file, void __user *argp)
> > +{
> > + struct super_block *sb = file_inode(file)->i_sb;
> > +
> > + if (!sb->s_uuid_len)
> > + return -ENOIOCTLCMD;
> > +
> > + struct fsuuid2 u = { .len = sb->s_uuid_len, };
> > + memcpy(&u.uuid[0], &sb->s_uuid, sb->s_uuid_len);
> > +
> > + return copy_to_user(argp, &u, sizeof(u)) ? -EFAULT : 0;
> > +}
>
> Can we please keep the declarations separate from the code? I always
> find this sort of implicit scoping of variables both difficult to
> read (especially in larger functions) and a landmine waiting to be
> tripped over. This could easily just be:
>
> static int ioctl_getfsuuid(struct file *file, void __user *argp)
> {
> struct super_block *sb = file_inode(file)->i_sb;
> struct fsuuid2 u = { .len = sb->s_uuid_len, };
>
> ....
>
> and then it's consistent with all the rest of the code...
The way I'm doing it here is actually what I'm transitioning my own code
to - the big reason being that always declaring variables at the tops of
functions leads to separating declaration and initialization, and worse
it leads people to declaring a variable once and reusing it for multiple
things (I've seen that be a source of real bugs too many times).
But I won't push that in this patch, we can just keep the style
consistent for now.
> > +/* Returns the external filesystem UUID, the same one blkid returns */
> > +#define FS_IOC_GETFSUUID _IOR(0x12, 142, struct fsuuid2)
> > +
>
> Can you add a comment somewhere in the file saying that new VFS
> ioctls should use the "0x12" namespace in the range 142-255, and
> mention that BLK ioctls should be kept within the 0x12 {0-141}
> range?
Well, if we're going to try to keep the BLK_ and FS_IOC_ ioctls in
separate ranges, then FS_IOC_ needs to move to something else becasue
otherwise BLK_ won't have a way to expand.
So what else -
ioctl-number.rst has a bunch of other ranges listed for fs.h, but 0x12
appears to be the only one without conflicts - all the other ranges seem
to have originated with other filesystems.
So perhaps I will take Darrick's nak (0x15) suggestion after all.
