linux-kernel - Re: [PATCH 1/7] Add a new flags-accepting interface for anonymous inodes

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Date:   Mon, 14 Oct 2019 11:15:30 -0700
From:   Daniel Colascione <dancol@...gle.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Linux API <linux-api@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Nick Kralevich <nnk@...gle.com>,
        Nosh Minwalla <nosh@...gle.com>,
        Tim Murray <timmurray@...gle.com>
Subject: Re: [PATCH 1/7] Add a new flags-accepting interface for anonymous inodes

Thanks for taking a look

On Mon, Oct 14, 2019 at 8:39 AM Jann Horn <jannh@...gle.com> wrote:
>
> On Sat, Oct 12, 2019 at 9:16 PM Daniel Colascione <dancol@...gle.com> wrote:
> > Add functions forwarding from the old names to the new ones so we
> > don't need to change any callers.
>
> This patch does more than the commit message says; it also refactors
> the body of the function. (I would've moved that refactoring over into
> patch 2, but I guess this works, too.)
>
> [...]
> > -struct file *anon_inode_getfile(const char *name,
> > -                               const struct file_operations *fops,
> > -                               void *priv, int flags)
> > +struct file *anon_inode_getfile2(const char *name,
> > +                                const struct file_operations *fops,
> > +                                void *priv, int flags, int anon_inode_flags)
>
> (AFAIK, normal kernel style is to slap a "__" prefix in front of the
> function name instead of appending a digit, but I guess it doesn't
> really matter.)

I thought prefixing "_" was for signaling "this is an implementation
detail and you probably don't want to call it unless you know what
you're doing", not "here's a new version that does a new thing".

> >  {
> > +       struct inode *inode;
> >         struct file *file;
> >
> > -       if (IS_ERR(anon_inode_inode))
> > -               return ERR_PTR(-ENODEV);
> > -
> > -       if (fops->owner && !try_module_get(fops->owner))
> > -               return ERR_PTR(-ENOENT);
> > +       if (anon_inode_flags)
> > +               return ERR_PTR(-EINVAL);
> >
> > +       inode = anon_inode_inode;
> > +       if (IS_ERR(inode))
> > +               return ERR_PTR(-ENODEV);
> >         /*
> > -        * We know the anon_inode inode count is always greater than zero,
> > -        * so ihold() is safe.
> > +        * We know the anon_inode inode count is always
> > +        * greater than zero, so ihold() is safe.
> >          */
>
> This looks like maybe you started editing the comment, then un-did the
> change, but left the modified line wrapping in your patch? Please
> avoid that - code changes with no real reason make "git blame" output
> more annoying and create trouble when porting patches between kernel
> versions.

I'll fix it.

>
> [...]
> >  EXPORT_SYMBOL_GPL(anon_inode_getfile);
> > +EXPORT_SYMBOL_GPL(anon_inode_getfile2);
> [...]
> >  EXPORT_SYMBOL_GPL(anon_inode_getfd);
> > +EXPORT_SYMBOL_GPL(anon_inode_getfd2);
>
> Since anon_inode_getfd() is now a static inline function in
> include/linux/anon_inodes.h, exporting it doesn't make sense anymore.
> Same for anon_inode_getfile().

I didn't want to break modules unnecessarily. Declaring the function
inline and also exporting it gives us an efficiency win while avoiding
an ABI break, right?

> [...]
> > +#define ANON_INODE_SECURE 1
>
> That #define belongs in a later patch, right?

Yep.