Re: [PATCH RFC] Introduce uniptr_t as a generic "universal" pointer

[Takashi Iwai]

On Wed, 09 Aug 2023 16:38:01 +0200,
Christoph Hellwig wrote:
> 
> On Wed, Aug 09, 2023 at 04:35:47PM +0200, Takashi Iwai wrote:
> > Although sockptr_t is used already in several places as a "universal"
> > pointer, it's still too confusing to use it in other subsystems, since
> > people see it always as if it were a network-related stuff.
> > 
> > This patch defines a more generic type, uniptr_t, that does exactly as
> > same as sockptr_t for a wider use.  As of now, it's almost 1:1 copy
> > with renames (just with comprehensive header file inclusions).
> 
> The original set_fs removal series did that as uptr_t, and Linus
> hated it with passion.  I somehow doubt he's going to like it more now.

Ah, good to know!

The remaining question is whether the use of sockptr_t for other
subsystems as a generic pointer is a recommended / acceptable move...


Takashi

> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > ---
> > 
> > This is a RFC patch, or rather a material for bikeshedding.
> > 
> > Initially the discussion started from the use of sockptr_t for the
> > sound driver in Andy's patch:
> >   https://lore.kernel.org/r/20230721100146.67293-1-andriy.shevchenko@xxxxxxxxxxxxxxx
> > followed by a bigger series of patches by me:
> >   https://lore.kernel.org/r/20230731154718.31048-1-tiwai@xxxxxxx
> > 
> > The first reaction to the patches (including my own) were
> > "why sockptr_t?"  Yes, it's just confusing.  So, here it is, a
> > proposal of defining the new type for the very purpose as sockptr_t.
> > 
> > The name of uniptr_t is nothing but my random pick up, and we can
> > endlessly discuss for a better name (genptr_t or whatever).
> > I'm totally open for the name.
> > 
> > After this introduction, sockptr_t can be alias of uniptr_t,
> > e.g. simply override with "#define sockptr_t uniptr_t" or such.
> > How can it be is another open question.
> > 
> > Also, we can clean up the macro implementation along with it;
> > there seem a few (rather minor) issues as suggested by Andy:
> >   https://lore.kernel.org/r/ZMlGKy7ibjkQ6ii7@xxxxxxxxxxxxxxxxxx
> > 
> > Honestly speaking, I don't mind to keep using sockptr_t generically
> > despite of the name, if people agree.  The rename might make sense,
> > though, if it's more widely used in other subsystems in future.
> > 
> > 
> > Takashi
> > 
> > ===
> > 
> >  include/linux/uniptr.h | 121 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 121 insertions(+)
> >  create mode 100644 include/linux/uniptr.h
> > 
> > diff --git a/include/linux/uniptr.h b/include/linux/uniptr.h
> > new file mode 100644
> > index 000000000000..f7994d3a45eb
> > --- /dev/null
> > +++ b/include/linux/uniptr.h
> > @@ -0,0 +1,121 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Support for "universal" pointers that can point to either kernel or userspace
> > + * memory.
> > + *
> > + * Original code from sockptr.h
> > + *    Copyright (c) 2020 Christoph Hellwig
> > + */
> > +#ifndef _LINUX_UNIPTR_H
> > +#define _LINUX_UNIPTR_H
> > +
> > +#include <linux/err.h>
> > +#include <linux/slab.h>
> > +#include <linux/string.h>
> > +#include <linux/types.h>
> > +#include <linux/uaccess.h>
> > +
> > +typedef struct {
> > +	union {
> > +		void		*kernel;
> > +		void __user	*user;
> > +	};
> > +	bool		is_kernel : 1;
> > +} uniptr_t;
> > +
> > +static inline bool uniptr_is_kernel(uniptr_t uniptr)
> > +{
> > +	return uniptr.is_kernel;
> > +}
> > +
> > +static inline uniptr_t KERNEL_UNIPTR(void *p)
> > +{
> > +	return (uniptr_t) { .kernel = p, .is_kernel = true };
> > +}
> > +
> > +static inline uniptr_t USER_UNIPTR(void __user *p)
> > +{
> > +	return (uniptr_t) { .user = p };
> > +}
> > +
> > +static inline bool uniptr_is_null(uniptr_t uniptr)
> > +{
> > +	if (uniptr_is_kernel(uniptr))
> > +		return !uniptr.kernel;
> > +	return !uniptr.user;
> > +}
> > +
> > +static inline int copy_from_uniptr_offset(void *dst, uniptr_t src,
> > +					  size_t offset, size_t size)
> > +{
> > +	if (!uniptr_is_kernel(src))
> > +		return copy_from_user(dst, src.user + offset, size);
> > +	memcpy(dst, src.kernel + offset, size);
> > +	return 0;
> > +}
> > +
> > +static inline int copy_from_uniptr(void *dst, uniptr_t src, size_t size)
> > +{
> > +	return copy_from_uniptr_offset(dst, src, 0, size);
> > +}
> > +
> > +static inline int copy_to_uniptr_offset(uniptr_t dst, size_t offset,
> > +					const void *src, size_t size)
> > +{
> > +	if (!uniptr_is_kernel(dst))
> > +		return copy_to_user(dst.user + offset, src, size);
> > +	memcpy(dst.kernel + offset, src, size);
> > +	return 0;
> > +}
> > +
> > +static inline int copy_to_uniptr(uniptr_t dst, const void *src, size_t size)
> > +{
> > +	return copy_to_uniptr_offset(dst, 0, src, size);
> > +}
> > +
> > +static inline void *memdup_uniptr(uniptr_t src, size_t len)
> > +{
> > +	void *p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
> > +
> > +	if (!p)
> > +		return ERR_PTR(-ENOMEM);
> > +	if (copy_from_uniptr(p, src, len)) {
> > +		kfree(p);
> > +		return ERR_PTR(-EFAULT);
> > +	}
> > +	return p;
> > +}
> > +
> > +static inline void *memdup_uniptr_nul(uniptr_t src, size_t len)
> > +{
> > +	char *p = kmalloc_track_caller(len + 1, GFP_KERNEL);
> > +
> > +	if (!p)
> > +		return ERR_PTR(-ENOMEM);
> > +	if (copy_from_uniptr(p, src, len)) {
> > +		kfree(p);
> > +		return ERR_PTR(-EFAULT);
> > +	}
> > +	p[len] = '\0';
> > +	return p;
> > +}
> > +
> > +static inline long strncpy_from_uniptr(char *dst, uniptr_t src, size_t count)
> > +{
> > +	if (uniptr_is_kernel(src)) {
> > +		size_t len = min(strnlen(src.kernel, count - 1) + 1, count);
> > +
> > +		memcpy(dst, src.kernel, len);
> > +		return len;
> > +	}
> > +	return strncpy_from_user(dst, src.user, count);
> > +}
> > +
> > +static inline int check_zeroed_uniptr(uniptr_t src, size_t offset, size_t size)
> > +{
> > +	if (!uniptr_is_kernel(src))
> > +		return check_zeroed_user(src.user + offset, size);
> > +	return memchr_inv(src.kernel + offset, 0, size) == NULL;
> > +}
> > +
> > +#endif /* _LINUX_UNIPTR_H */
> > -- 
> > 2.35.3
> ---end quoted text---
>