Re: [RESEND PATCH v2] hfsplus: prevent negative dentries when casefolded

[Chung-Chiang Cheng]

This function revalidates dentries without blocking and storing to the
dentry. As the document mentioned [1], I think it's safe in rcu-walk
mode. I also found jfs_ci_revalidate() takes the same approach.

        d_revalidate may be called in rcu-walk mode (flags & LOOKUP_RCU).
        If in rcu-walk mode, the filesystem must revalidate the dentry 
without
        blocking or storing to the dentry, d_parent and d_inode should 
not be
        used without care (because they can change and, in d_inode 
case, even
        become NULL under us


[1] https://www.kernel.org/doc/Documentation/filesystems/vfs.txt

Thanks,
C.C.Cheng

> > +
> > +int hfsplus_revalidate_dentry(struct dentry *dentry, unsigned int flags)
> > +{
> What’s about this code?
>
> If (flags & LOOKUP_RCU)
>     return -ECHILD;
>
> Do we really need to miss it here?
>
> Thanks,
> Slava.
>
>
> > +	/*
> > +	 * dentries are always valid when disabling casefold.
> > +	 */
> > +	if (!test_bit(HFSPLUS_SB_CASEFOLD, &HFSPLUS_SB(dentry->d_sb)->flags))
> > +		return 1;
> > +
> > +	/*
> > +	 * Positive dentries are valid when enabling casefold.
> > +	 *
> > +	 * Note, rename() to existing directory entry will have ->d_inode, and
> > +	 * will use existing name which isn't specified name by user.
> > +	 *
> > +	 * We may be able to drop this positive dentry here. But dropping
> > +	 * positive dentry isn't good idea. So it's unsupported like
> > +	 * rename("filename", "FILENAME") for now.
> > +	 */
> > +	if (d_really_is_positive(dentry))
> > +		return 1;
> > +
> > +	/*
> > +	 * Drop the negative dentry, in order to make sure to use the case
> > +	 * sensitive name which is specified by user if this is for creation.
> > +	 */
> > +	if (flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET))
> > +		return 0;
> > +
> > +	return 1;
> > +}
> > --
> > 2.25.1