Re: [RFC] struct fd situation

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, May 31, 2024 at 05:30:45PM +0100, Al Viro wrote:
> static inline struct fd_err file_fd_err(struct file *f, bool is_cloned)
> {
> 	if (IS_ERR(f))
> 		return (struct fd_err){PTR_ERR(f)};
> 	else
> 		return (struct fd_err){(unsigned long)f | is_cloned};
> }
> 
> (or, perhaps, file_fd_cloned and file_fd_borrowed, to get rid of
> 'is_cloned' argument in public API; need to play around a bit and
> see what works better - the interesting part is what the constructor
> for struct fd would look like)

... along with

static inline struct fd_err ERR_FD(long n)
{
	return (struct fd_err){.word = (unsigned long)n};
}

yielding

> static struct fd_err ovl_real_fdget_meta(const struct file *file, bool allow_meta)
> {
>         struct dentry *dentry = file_dentry(file);
>         struct path realpath;
>         int err;
> 
>         if (allow_meta) {
>                 ovl_path_real(dentry, &realpath);
>         } else {
>                 /* lazy lookup and verify of lowerdata */
>                 err = ovl_verify_lowerdata(dentry);
>                 if (err)
			return ERR_FD(err);
> 
>                 ovl_path_realdata(dentry, &realpath);
>         }
>         if (!realpath.dentry)
		return ERR_FD(-EIO);
> 
>         /* Has it been copied up since we'd opened it? */
>         if (unlikely(file_inode(real->file) != d_inode(realpath.dentry)))
		return file_fd_cloned(ovl_open_realfile(file, &realpath));
> 
>         /* Did the flags change since open? */
>         if (unlikely((file->f_flags ^ real->file->f_flags) & ~OVL_OPEN_FLAGS)) {
> 		err = ovl_change_flags(real->file, file->f_flags);
> 		if (err)
			return ERR_FD(err);
> 	}
> 
	return file_fd_borrowed(file->private_data);
> }