[PATCH bpf-next 0/2] libbpf/xsk cleanups

[PATCH bpf-next 0/2] libbpf/xsk cleanups

[Björn Töpel]

This series removes a header dependency from xsk.h, and moves
libbpf_util.h into xsk.h.

More details in each commit!


Thank you,
Björn

Björn Töpel (2):
  libbpf: xsk: remove linux/compiler.h header
  libbpf: xsk: move barriers from libbpf_util.h to xsk.h

 tools/lib/bpf/Makefile      |  1 -
 tools/lib/bpf/libbpf_util.h | 75 -------------------------------------
 tools/lib/bpf/xsk.h         | 68 ++++++++++++++++++++++++++++++++-
 3 files changed, 67 insertions(+), 77 deletions(-)
 delete mode 100644 tools/lib/bpf/libbpf_util.h


base-commit: 32f91529e2bdbe0d92edb3ced41dfba4beffa84a
-- 
2.27.0

[PATCH bpf-next 1/2] libbpf: xsk: remove linux/compiler.h header

[Björn Töpel]

From: Björn Töpel <bjorn.topel@intel.com>

In commit 291471dd1559 ("libbpf, xsk: Add libbpf_smp_store_release
libbpf_smp_load_acquire") linux/compiler.h was added as a dependency
to xsk.h, which is the user-facing API. This makes it harder for
userspace application to consume the library. Here the header
inclusion is removed, and instead {READ,WRITE}_ONCE() is added
explicitly.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 tools/lib/bpf/libbpf_util.h | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/libbpf_util.h b/tools/lib/bpf/libbpf_util.h
index cfbcfc063c81..954da9b34a34 100644
--- a/tools/lib/bpf/libbpf_util.h
+++ b/tools/lib/bpf/libbpf_util.h
@@ -5,25 +5,30 @@
 #define __LIBBPF_LIBBPF_UTIL_H
 
 #include <stdbool.h>
-#include <linux/compiler.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-/* Use these barrier functions instead of smp_[rw]mb() when they are
- * used in a libbpf header file. That way they can be built into the
- * application that uses libbpf.
+/* Load-Acquire Store-Release barriers used by the XDP socket
+ * library. The following macros should *NOT* be considered part of
+ * the xsk.h API, and is subject to change anytime.
+ *
+ * LIBRARY INTERNAL
  */
+
+#define __XSK_READ_ONCE(x) (*(volatile typeof(x) *)&x)
+#define __XSK_WRITE_ONCE(x, v) (*(volatile typeof(x) *)&x) = (v)
+
 #if defined(__i386__) || defined(__x86_64__)
 # define libbpf_smp_store_release(p, v)					\
 	do {								\
 		asm volatile("" : : : "memory");			\
-		WRITE_ONCE(*p, v);					\
+		__XSK_WRITE_ONCE(*p, v);				\
 	} while (0)
 # define libbpf_smp_load_acquire(p)					\
 	({								\
-		typeof(*p) ___p1 = READ_ONCE(*p);			\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
 		asm volatile("" : : : "memory");			\
 		___p1;							\
 	})
@@ -41,11 +46,11 @@ extern "C" {
 # define libbpf_smp_store_release(p, v)					\
 	do {								\
 		asm volatile ("fence rw,w" : : : "memory");		\
-		WRITE_ONCE(*p, v);					\
+		__XSK_WRITE_ONCE(*p, v);				\
 	} while (0)
 # define libbpf_smp_load_acquire(p)					\
 	({								\
-		typeof(*p) ___p1 = READ_ONCE(*p);			\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
 		asm volatile ("fence r,rw" : : : "memory");		\
 		___p1;							\
 	})
@@ -55,19 +60,21 @@ extern "C" {
 #define libbpf_smp_store_release(p, v)					\
 	do {								\
 		__sync_synchronize();					\
-		WRITE_ONCE(*p, v);					\
+		__XSK_WRITE_ONCE(*p, v);				\
 	} while (0)
 #endif
 
 #ifndef libbpf_smp_load_acquire
 #define libbpf_smp_load_acquire(p)					\
 	({								\
-		typeof(*p) ___p1 = READ_ONCE(*p);			\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
 		__sync_synchronize();					\
 		___p1;							\
 	})
 #endif
 
+/* LIBRARY INTERNAL -- END */
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
-- 
2.27.0

[PATCH bpf-next 2/2] libbpf: xsk: move barriers from libbpf_util.h to xsk.h

[Björn Töpel]

From: Björn Töpel <bjorn.topel@intel.com>

The only user of libbpf_util.h is xsk.h. Move the barriers to xsk.h,
and remove libbpf_util.h. The barriers are used as an implementation
detail, and should not be considered part of the stable API.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 tools/lib/bpf/Makefile      |  1 -
 tools/lib/bpf/libbpf_util.h | 82 -------------------------------------
 tools/lib/bpf/xsk.h         | 68 +++++++++++++++++++++++++++++-
 3 files changed, 67 insertions(+), 84 deletions(-)
 delete mode 100644 tools/lib/bpf/libbpf_util.h

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 8170f88e8ea6..f45bacbaa3d5 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -228,7 +228,6 @@ install_headers: $(BPF_HELPER_DEFS)
 		$(call do_install,bpf.h,$(prefix)/include/bpf,644); \
 		$(call do_install,libbpf.h,$(prefix)/include/bpf,644); \
 		$(call do_install,btf.h,$(prefix)/include/bpf,644); \
-		$(call do_install,libbpf_util.h,$(prefix)/include/bpf,644); \
 		$(call do_install,libbpf_common.h,$(prefix)/include/bpf,644); \
 		$(call do_install,xsk.h,$(prefix)/include/bpf,644); \
 		$(call do_install,bpf_helpers.h,$(prefix)/include/bpf,644); \
diff --git a/tools/lib/bpf/libbpf_util.h b/tools/lib/bpf/libbpf_util.h
deleted file mode 100644
index 954da9b34a34..000000000000
--- a/tools/lib/bpf/libbpf_util.h
+++ /dev/null
@@ -1,82 +0,0 @@
-/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
-/* Copyright (c) 2019 Facebook */
-
-#ifndef __LIBBPF_LIBBPF_UTIL_H
-#define __LIBBPF_LIBBPF_UTIL_H
-
-#include <stdbool.h>
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-/* Load-Acquire Store-Release barriers used by the XDP socket
- * library. The following macros should *NOT* be considered part of
- * the xsk.h API, and is subject to change anytime.
- *
- * LIBRARY INTERNAL
- */
-
-#define __XSK_READ_ONCE(x) (*(volatile typeof(x) *)&x)
-#define __XSK_WRITE_ONCE(x, v) (*(volatile typeof(x) *)&x) = (v)
-
-#if defined(__i386__) || defined(__x86_64__)
-# define libbpf_smp_store_release(p, v)					\
-	do {								\
-		asm volatile("" : : : "memory");			\
-		__XSK_WRITE_ONCE(*p, v);				\
-	} while (0)
-# define libbpf_smp_load_acquire(p)					\
-	({								\
-		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
-		asm volatile("" : : : "memory");			\
-		___p1;							\
-	})
-#elif defined(__aarch64__)
-# define libbpf_smp_store_release(p, v)					\
-		asm volatile ("stlr %w1, %0" : "=Q" (*p) : "r" (v) : "memory")
-# define libbpf_smp_load_acquire(p)					\
-	({								\
-		typeof(*p) ___p1;					\
-		asm volatile ("ldar %w0, %1"				\
-			      : "=r" (___p1) : "Q" (*p) : "memory");	\
-		___p1;							\
-	})
-#elif defined(__riscv)
-# define libbpf_smp_store_release(p, v)					\
-	do {								\
-		asm volatile ("fence rw,w" : : : "memory");		\
-		__XSK_WRITE_ONCE(*p, v);				\
-	} while (0)
-# define libbpf_smp_load_acquire(p)					\
-	({								\
-		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
-		asm volatile ("fence r,rw" : : : "memory");		\
-		___p1;							\
-	})
-#endif
-
-#ifndef libbpf_smp_store_release
-#define libbpf_smp_store_release(p, v)					\
-	do {								\
-		__sync_synchronize();					\
-		__XSK_WRITE_ONCE(*p, v);				\
-	} while (0)
-#endif
-
-#ifndef libbpf_smp_load_acquire
-#define libbpf_smp_load_acquire(p)					\
-	({								\
-		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
-		__sync_synchronize();					\
-		___p1;							\
-	})
-#endif
-
-/* LIBRARY INTERNAL -- END */
-
-#ifdef __cplusplus
-} /* extern "C" */
-#endif
-
-#endif
diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index a9fdea87b5cd..1d846a419d21 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -4,6 +4,7 @@
  * AF_XDP user-space access library.
  *
  * Copyright(c) 2018 - 2019 Intel Corporation.
+ * Copyright (c) 2019 Facebook
  *
  * Author(s): Magnus Karlsson <magnus.karlsson@intel.com>
  */
@@ -13,15 +14,80 @@
 
 #include <stdio.h>
 #include <stdint.h>
+#include <stdbool.h>
 #include <linux/if_xdp.h>
 
 #include "libbpf.h"
-#include "libbpf_util.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/* Load-Acquire Store-Release barriers used by the XDP socket
+ * library. The following macros should *NOT* be considered part of
+ * the xsk.h API, and is subject to change anytime.
+ *
+ * LIBRARY INTERNAL
+ */
+
+#define __XSK_READ_ONCE(x) (*(volatile typeof(x) *)&x)
+#define __XSK_WRITE_ONCE(x, v) (*(volatile typeof(x) *)&x) = (v)
+
+#if defined(__i386__) || defined(__x86_64__)
+# define libbpf_smp_store_release(p, v)					\
+	do {								\
+		asm volatile("" : : : "memory");			\
+		__XSK_WRITE_ONCE(*p, v);				\
+	} while (0)
+# define libbpf_smp_load_acquire(p)					\
+	({								\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
+		asm volatile("" : : : "memory");			\
+		___p1;							\
+	})
+#elif defined(__aarch64__)
+# define libbpf_smp_store_release(p, v)					\
+		asm volatile ("stlr %w1, %0" : "=Q" (*p) : "r" (v) : "memory")
+# define libbpf_smp_load_acquire(p)					\
+	({								\
+		typeof(*p) ___p1;					\
+		asm volatile ("ldar %w0, %1"				\
+			      : "=r" (___p1) : "Q" (*p) : "memory");	\
+		___p1;							\
+	})
+#elif defined(__riscv)
+# define libbpf_smp_store_release(p, v)					\
+	do {								\
+		asm volatile ("fence rw,w" : : : "memory");		\
+		__XSK_WRITE_ONCE(*p, v);				\
+	} while (0)
+# define libbpf_smp_load_acquire(p)					\
+	({								\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
+		asm volatile ("fence r,rw" : : : "memory");		\
+		___p1;							\
+	})
+#endif
+
+#ifndef libbpf_smp_store_release
+#define libbpf_smp_store_release(p, v)					\
+	do {								\
+		__sync_synchronize();					\
+		__XSK_WRITE_ONCE(*p, v);				\
+	} while (0)
+#endif
+
+#ifndef libbpf_smp_load_acquire
+#define libbpf_smp_load_acquire(p)					\
+	({								\
+		typeof(*p) ___p1 = __XSK_READ_ONCE(*p);			\
+		__sync_synchronize();					\
+		___p1;							\
+	})
+#endif
+
+/* LIBRARY INTERNAL -- END */
+
 /* Do not access these members directly. Use the functions below. */
 #define DEFINE_XSK_RING(name) \
 struct name { \
-- 
2.27.0

Re: [PATCH bpf-next 2/2] libbpf: xsk: move barriers from libbpf_util.h to xsk.h

[Andrii Nakryiko]

On Wed, Mar 10, 2021 at 12:09 AM Björn Töpel <bjorn.topel@gmail.com> wrote:
>
> From: Björn Töpel <bjorn.topel@intel.com>
>
> The only user of libbpf_util.h is xsk.h. Move the barriers to xsk.h,
> and remove libbpf_util.h. The barriers are used as an implementation
> detail, and should not be considered part of the stable API.
>
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
> ---
>  tools/lib/bpf/Makefile      |  1 -
>  tools/lib/bpf/libbpf_util.h | 82 -------------------------------------
>  tools/lib/bpf/xsk.h         | 68 +++++++++++++++++++++++++++++-
>  3 files changed, 67 insertions(+), 84 deletions(-)
>  delete mode 100644 tools/lib/bpf/libbpf_util.h
>

[...]

> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> index a9fdea87b5cd..1d846a419d21 100644
> --- a/tools/lib/bpf/xsk.h
> +++ b/tools/lib/bpf/xsk.h
> @@ -4,6 +4,7 @@
>   * AF_XDP user-space access library.
>   *
>   * Copyright(c) 2018 - 2019 Intel Corporation.

Couldn't unsee ^this mismatch. Added space there.

Also, removing libbpf_util.h caused incremental build failure for the
kernel due to cached dependency files. make clean solved the issue. So
just FYI for everyone.

Applied to bpf-next, thanks.

> + * Copyright (c) 2019 Facebook
>   *
>   * Author(s): Magnus Karlsson <magnus.karlsson@intel.com>
>   */
> @@ -13,15 +14,80 @@
>
>  #include <stdio.h>
>  #include <stdint.h>
> +#include <stdbool.h>
>  #include <linux/if_xdp.h>
>
>  #include "libbpf.h"
> -#include "libbpf_util.h"
>
>  #ifdef __cplusplus
>  extern "C" {
>  #endif
>

[...]

Re: [PATCH bpf-next 2/2] libbpf: xsk: move barriers from libbpf_util.h to xsk.h

[Jonathan Lemon]

On Wed, Mar 10, 2021 at 09:09:29AM +0100, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@intel.com>
> 
> The only user of libbpf_util.h is xsk.h. Move the barriers to xsk.h,
> and remove libbpf_util.h. The barriers are used as an implementation
> detail, and should not be considered part of the stable API.

Does that mean that anything else which uses the same type of
shared rings (bpf ringbuffer, io_uring, zctap) have to implement
the same primitives that xsk.h has?
-- 
Jonathan

Re: [PATCH bpf-next 2/2] libbpf: xsk: move barriers from libbpf_util.h to xsk.h

[Björn Töpel]

On 2021-03-11 01:06, Jonathan Lemon wrote:
> On Wed, Mar 10, 2021 at 09:09:29AM +0100, Björn Töpel wrote:
>> From: Björn Töpel <bjorn.topel@intel.com>
>>
>> The only user of libbpf_util.h is xsk.h. Move the barriers to xsk.h,
>> and remove libbpf_util.h. The barriers are used as an implementation
>> detail, and should not be considered part of the stable API.
> 
> Does that mean that anything else which uses the same type of
> shared rings (bpf ringbuffer, io_uring, zctap) have to implement
> the same primitives that xsk.h has?
> 

Jonathan, there's a longer explanation on back-/forward-compatibility in
the commit message [1]. Again, this is for the XDP socket rings, so I
wont comment on the other rings. I would not assume compatibility
between different rings (e.g. the bpf ringbuffer and XDP sockets rings),
not even prior the barrier change.


Björn

[1] 
https://lore.kernel.org/bpf/20210305094113.413544-2-bjorn.topel@gmail.com/ 

Re: [PATCH bpf-next 2/2] libbpf: xsk: move barriers from libbpf_util.h to xsk.h

[Andrii Nakryiko]

On Wed, Mar 10, 2021 at 10:59 PM Björn Töpel <bjorn.topel@intel.com> wrote:
>
> On 2021-03-11 01:06, Jonathan Lemon wrote:
> > On Wed, Mar 10, 2021 at 09:09:29AM +0100, Björn Töpel wrote:
> >> From: Björn Töpel <bjorn.topel@intel.com>
> >>
> >> The only user of libbpf_util.h is xsk.h. Move the barriers to xsk.h,
> >> and remove libbpf_util.h. The barriers are used as an implementation
> >> detail, and should not be considered part of the stable API.
> >
> > Does that mean that anything else which uses the same type of
> > shared rings (bpf ringbuffer, io_uring, zctap) have to implement
> > the same primitives that xsk.h has?
> >
>
> Jonathan, there's a longer explanation on back-/forward-compatibility in
> the commit message [1]. Again, this is for the XDP socket rings, so I
> wont comment on the other rings. I would not assume compatibility
> between different rings (e.g. the bpf ringbuffer and XDP sockets rings),
> not even prior the barrier change.
>
>

BPF ringbuf is using smp_store_release()/smp_load_acquire(), which are
coming from asm/barrier.h. But libbpf abstracts all the low-level
details, so users don't have to use such low-level primitives
directly.

> Björn
>
> [1]
> https://lore.kernel.org/bpf/20210305094113.413544-2-bjorn.topel@gmail.com/
>