[PATCH] libbpf: export inline helpers as symbols for xsk

[PATCH] libbpf: export inline helpers as symbols for xsk

[Kumar Kartikeya Dwivedi]

This helps people writing language bindings to not have to rewrite C
wrappers for inline functions in the headers. We force inline the
definition from the header for C and C++ consumers, but also export a
symbol in the library for others. This keeps the performance
advantages similar to using static inline, while also allowing tools
like Rust's bindgen to generate wrappers for the functions.

Also see
https://lore.kernel.org/bpf/CAJ8uoz0QqR97qEYYK=VVCE9A=V=k2tKnH6wNM48jeak2RAmL0A@mail.gmail.com/
for some context.

Also see https://github.com/xdp-project/xdp-tools/pull/97 for more
discussion on the same.

extern inline is used as it's slightly better since it warns when an
inline definition is missing.

The fvisibility attribute goes on the inline definition, as essentially
it acts as a declaration for the function, while the extern inline
declaration ends up acting as a definition.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 tools/lib/bpf/libbpf.map | 16 ++++++++++++++
 tools/lib/bpf/xsk.c      | 24 +++++++++++++++++++++
 tools/lib/bpf/xsk.h      | 45 +++++++++++++++++++++++-----------------
 3 files changed, 66 insertions(+), 19 deletions(-)

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index b9b29baf1df8..52ece4296f4b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -361,4 +361,20 @@ LIBBPF_0.4.0 {
 		bpf_linker__new;
 		bpf_map__inner_map;
 		bpf_object__set_kversion;
+		xsk_cons_nb_avail;
+		xsk_prod_nb_free;
+		xsk_ring_cons__cancel;
+		xsk_ring_cons__comp_addr;
+		xsk_ring_cons__peek;
+		xsk_ring_cons__release;
+		xsk_ring_cons__rx_desc;
+		xsk_ring_prod__fill_addr;
+		xsk_ring_prod__needs_wakeup;
+		xsk_ring_prod__reserve;
+		xsk_ring_prod__submit;
+		xsk_ring_prod__tx_desc;
+		xsk_umem__add_offset_to_addr;
+		xsk_umem__extract_addr;
+		xsk_umem__extract_offset;
+		xsk_umem__get_data;
 } LIBBPF_0.3.0;
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 95da0e19f4a5..ebe370837024 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -107,6 +107,30 @@ struct xdp_mmap_offsets_v1 {
 	struct xdp_ring_offset_v1 cr;
 };
 
+/* Export all inline helpers as symbols for use by language bindings. */
+extern inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill,
+					      __u32 idx);
+extern inline const __u64 *
+xsk_ring_cons__comp_addr(const struct xsk_ring_cons *comp, __u32 idx);
+extern inline struct xdp_desc *xsk_ring_prod__tx_desc(struct xsk_ring_prod *tx,
+						      __u32 idx);
+extern inline const struct xdp_desc *
+xsk_ring_cons__rx_desc(const struct xsk_ring_cons *rx, __u32 idx);
+extern inline int xsk_ring_prod__needs_wakeup(const struct xsk_ring_prod *r);
+extern inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb);
+extern inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb);
+extern inline __u32 xsk_ring_prod__reserve(struct xsk_ring_prod *prod, __u32 nb,
+					   __u32 *idx);
+extern inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb);
+extern inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb,
+					__u32 *idx);
+extern inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons, __u32 nb);
+extern inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, __u32 nb);
+extern inline void *xsk_umem__get_data(void *umem_area, __u64 addr);
+extern inline __u64 xsk_umem__extract_addr(__u64 addr);
+extern inline __u64 xsk_umem__extract_offset(__u64 addr);
+extern inline __u64 xsk_umem__add_offset_to_addr(__u64 addr);
+
 int xsk_umem__fd(const struct xsk_umem *umem)
 {
 	return umem ? umem->fd : -EINVAL;
diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 01c12dca9c10..8ab1d0453fbe 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -111,15 +111,15 @@ DEFINE_XSK_RING(xsk_ring_cons);
 struct xsk_umem;
 struct xsk_socket;
 
-static inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill,
-					      __u32 idx)
+LIBBPF_API __always_inline __u64 *
+xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill, __u32 idx)
 {
 	__u64 *addrs = (__u64 *)fill->ring;
 
 	return &addrs[idx & fill->mask];
 }
 
-static inline const __u64 *
+LIBBPF_API __always_inline const __u64 *
 xsk_ring_cons__comp_addr(const struct xsk_ring_cons *comp, __u32 idx)
 {
 	const __u64 *addrs = (const __u64 *)comp->ring;
@@ -127,15 +127,15 @@ xsk_ring_cons__comp_addr(const struct xsk_ring_cons *comp, __u32 idx)
 	return &addrs[idx & comp->mask];
 }
 
-static inline struct xdp_desc *xsk_ring_prod__tx_desc(struct xsk_ring_prod *tx,
-						      __u32 idx)
+LIBBPF_API __always_inline struct xdp_desc *
+xsk_ring_prod__tx_desc(struct xsk_ring_prod *tx, __u32 idx)
 {
 	struct xdp_desc *descs = (struct xdp_desc *)tx->ring;
 
 	return &descs[idx & tx->mask];
 }
 
-static inline const struct xdp_desc *
+LIBBPF_API __always_inline const struct xdp_desc *
 xsk_ring_cons__rx_desc(const struct xsk_ring_cons *rx, __u32 idx)
 {
 	const struct xdp_desc *descs = (const struct xdp_desc *)rx->ring;
@@ -143,12 +143,14 @@ xsk_ring_cons__rx_desc(const struct xsk_ring_cons *rx, __u32 idx)
 	return &descs[idx & rx->mask];
 }
 
-static inline int xsk_ring_prod__needs_wakeup(const struct xsk_ring_prod *r)
+LIBBPF_API __always_inline int
+xsk_ring_prod__needs_wakeup(const struct xsk_ring_prod *r)
 {
 	return *r->flags & XDP_RING_NEED_WAKEUP;
 }
 
-static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
+LIBBPF_API __always_inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r,
+						  __u32 nb)
 {
 	__u32 free_entries = r->cached_cons - r->cached_prod;
 
@@ -168,7 +170,8 @@ static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
 	return r->cached_cons - r->cached_prod;
 }
 
-static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
+LIBBPF_API __always_inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r,
+						   __u32 nb)
 {
 	__u32 entries = r->cached_prod - r->cached_cons;
 
@@ -180,7 +183,8 @@ static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
 	return (entries > nb) ? nb : entries;
 }
 
-static inline __u32 xsk_ring_prod__reserve(struct xsk_ring_prod *prod, __u32 nb, __u32 *idx)
+LIBBPF_API __always_inline __u32
+xsk_ring_prod__reserve(struct xsk_ring_prod *prod, __u32 nb, __u32 *idx)
 {
 	if (xsk_prod_nb_free(prod, nb) < nb)
 		return 0;
@@ -191,7 +195,8 @@ static inline __u32 xsk_ring_prod__reserve(struct xsk_ring_prod *prod, __u32 nb,
 	return nb;
 }
 
-static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb)
+LIBBPF_API __always_inline void
+xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb)
 {
 	/* Make sure everything has been written to the ring before indicating
 	 * this to the kernel by writing the producer pointer.
@@ -199,7 +204,8 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb)
 	libbpf_smp_store_release(prod->producer, *prod->producer + nb);
 }
 
-static inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb, __u32 *idx)
+LIBBPF_API __always_inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons,
+						     __u32 nb, __u32 *idx)
 {
 	__u32 entries = xsk_cons_nb_avail(cons, nb);
 
@@ -211,36 +217,37 @@ static inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb, __
 	return entries;
 }
 
-static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons, __u32 nb)
+LIBBPF_API __always_inline void
+xsk_ring_cons__cancel(struct xsk_ring_cons *cons, __u32 nb)
 {
 	cons->cached_cons -= nb;
 }
 
-static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, __u32 nb)
+LIBBPF_API __always_inline void
+xsk_ring_cons__release(struct xsk_ring_cons *cons, __u32 nb)
 {
 	/* Make sure data has been read before indicating we are done
 	 * with the entries by updating the consumer pointer.
 	 */
 	libbpf_smp_store_release(cons->consumer, *cons->consumer + nb);
-
 }
 
-static inline void *xsk_umem__get_data(void *umem_area, __u64 addr)
+LIBBPF_API __always_inline void *xsk_umem__get_data(void *umem_area, __u64 addr)
 {
 	return &((char *)umem_area)[addr];
 }
 
-static inline __u64 xsk_umem__extract_addr(__u64 addr)
+LIBBPF_API __always_inline __u64 xsk_umem__extract_addr(__u64 addr)
 {
 	return addr & XSK_UNALIGNED_BUF_ADDR_MASK;
 }
 
-static inline __u64 xsk_umem__extract_offset(__u64 addr)
+LIBBPF_API __always_inline __u64 xsk_umem__extract_offset(__u64 addr)
 {
 	return addr >> XSK_UNALIGNED_BUF_OFFSET_SHIFT;
 }
 
-static inline __u64 xsk_umem__add_offset_to_addr(__u64 addr)
+LIBBPF_API __always_inline __u64 xsk_umem__add_offset_to_addr(__u64 addr)
 {
 	return xsk_umem__extract_addr(addr) + xsk_umem__extract_offset(addr);
 }
-- 
2.30.2

Re: [PATCH] libbpf: export inline helpers as symbols for xsk

[Andrii Nakryiko]

On Mon, Apr 26, 2021 at 1:22 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> This helps people writing language bindings to not have to rewrite C
> wrappers for inline functions in the headers. We force inline the
> definition from the header for C and C++ consumers, but also export a
> symbol in the library for others. This keeps the performance
> advantages similar to using static inline, while also allowing tools
> like Rust's bindgen to generate wrappers for the functions.
>
> Also see
> https://lore.kernel.org/bpf/CAJ8uoz0QqR97qEYYK=VVCE9A=V=k2tKnH6wNM48jeak2RAmL0A@mail.gmail.com/
> for some context.
>
> Also see https://github.com/xdp-project/xdp-tools/pull/97 for more
> discussion on the same.
>
> extern inline is used as it's slightly better since it warns when an
> inline definition is missing.
>
> The fvisibility attribute goes on the inline definition, as essentially
> it acts as a declaration for the function, while the extern inline
> declaration ends up acting as a definition.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

xsk is moving into libxdp, why not do this there, instead of exporting
a lot of symbols that we'll be deprecating very soon. It will also
incentivise customers to make a move more promptly.

Bjorn, Magnus, what's the status of libxsk in libxdp?

>  tools/lib/bpf/libbpf.map | 16 ++++++++++++++
>  tools/lib/bpf/xsk.c      | 24 +++++++++++++++++++++
>  tools/lib/bpf/xsk.h      | 45 +++++++++++++++++++++++-----------------
>  3 files changed, 66 insertions(+), 19 deletions(-)
>

[...]

Re: [PATCH] libbpf: export inline helpers as symbols for xsk

[Magnus Karlsson]

On Tue, Apr 27, 2021 at 1:20 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Mon, Apr 26, 2021 at 1:22 PM Kumar Kartikeya Dwivedi
> <memxor@gmail.com> wrote:
> >
> > This helps people writing language bindings to not have to rewrite C
> > wrappers for inline functions in the headers. We force inline the
> > definition from the header for C and C++ consumers, but also export a
> > symbol in the library for others. This keeps the performance
> > advantages similar to using static inline, while also allowing tools
> > like Rust's bindgen to generate wrappers for the functions.
> >
> > Also see
> > https://lore.kernel.org/bpf/CAJ8uoz0QqR97qEYYK=VVCE9A=V=k2tKnH6wNM48jeak2RAmL0A@mail.gmail.com/
> > for some context.
> >
> > Also see https://github.com/xdp-project/xdp-tools/pull/97 for more
> > discussion on the same.
> >
> > extern inline is used as it's slightly better since it warns when an
> > inline definition is missing.
> >
> > The fvisibility attribute goes on the inline definition, as essentially
> > it acts as a declaration for the function, while the extern inline
> > declaration ends up acting as a definition.
> >
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > ---
>
> xsk is moving into libxdp, why not do this there, instead of exporting
> a lot of symbols that we'll be deprecating very soon. It will also
> incentivise customers to make a move more promptly.
>
> Bjorn, Magnus, what's the status of libxsk in libxdp?

There is a branch in the repo with the xsk support of libbpf
integrated into libxdp. But it has not been merged yet. Toke might
still have some comments on it, do not know, but we have been fixing a
number of issue during the past months (including one in Linux) so it
is stable and performs well now. A simple sample and some tests are
still missing. But the above Rust support is in that branch.

What is your current time plan on the libbpf 1.0 release? Before that
happens, I need to make the Linux samples and selftests self-contained
and not reliant on the xsk support in libbpf since it will be
disappearing. This basically amounts to moving the xsk libbpf
functionality into a separate file and using that from the samples and
tests. At this point in time, relying on the user having libxdp
installed would not be a good idea since if they do not (the majority
of people at this point I believe) it would break the build of
samples/bpf and selftests/bpf. Please let me know what you think?

> >  tools/lib/bpf/libbpf.map | 16 ++++++++++++++
> >  tools/lib/bpf/xsk.c      | 24 +++++++++++++++++++++
> >  tools/lib/bpf/xsk.h      | 45 +++++++++++++++++++++++-----------------
> >  3 files changed, 66 insertions(+), 19 deletions(-)
> >
>
> [...]

Re: [PATCH] libbpf: export inline helpers as symbols for xsk

[Andrii Nakryiko]

On Mon, Apr 26, 2021 at 11:49 PM Magnus Karlsson
<magnus.karlsson@gmail.com> wrote:
>
> On Tue, Apr 27, 2021 at 1:20 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Mon, Apr 26, 2021 at 1:22 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.com> wrote:
> > >
> > > This helps people writing language bindings to not have to rewrite C
> > > wrappers for inline functions in the headers. We force inline the
> > > definition from the header for C and C++ consumers, but also export a
> > > symbol in the library for others. This keeps the performance
> > > advantages similar to using static inline, while also allowing tools
> > > like Rust's bindgen to generate wrappers for the functions.
> > >
> > > Also see
> > > https://lore.kernel.org/bpf/CAJ8uoz0QqR97qEYYK=VVCE9A=V=k2tKnH6wNM48jeak2RAmL0A@mail.gmail.com/
> > > for some context.
> > >
> > > Also see https://github.com/xdp-project/xdp-tools/pull/97 for more
> > > discussion on the same.
> > >
> > > extern inline is used as it's slightly better since it warns when an
> > > inline definition is missing.
> > >
> > > The fvisibility attribute goes on the inline definition, as essentially
> > > it acts as a declaration for the function, while the extern inline
> > > declaration ends up acting as a definition.
> > >
> > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > > ---
> >
> > xsk is moving into libxdp, why not do this there, instead of exporting
> > a lot of symbols that we'll be deprecating very soon. It will also
> > incentivise customers to make a move more promptly.
> >
> > Bjorn, Magnus, what's the status of libxsk in libxdp?
>
> There is a branch in the repo with the xsk support of libbpf
> integrated into libxdp. But it has not been merged yet. Toke might
> still have some comments on it, do not know, but we have been fixing a
> number of issue during the past months (including one in Linux) so it
> is stable and performs well now. A simple sample and some tests are
> still missing. But the above Rust support is in that branch.
>
> What is your current time plan on the libbpf 1.0 release? Before that
> happens, I need to make the Linux samples and selftests self-contained
> and not reliant on the xsk support in libbpf since it will be
> disappearing. This basically amounts to moving the xsk libbpf
> functionality into a separate file and using that from the samples and
> tests. At this point in time, relying on the user having libxdp
> installed would not be a good idea since if they do not (the majority
> of people at this point I believe) it would break the build of
> samples/bpf and selftests/bpf. Please let me know what you think?

I'm hoping to finish BPF static linker work and then will start doing
libbpf 1.0 work. xsk.c stuff is not going away in at least next few
months. My objection is to keep extending that functionality in libbpf
if we are actively working on having all of that in libxdp.

>
> > >  tools/lib/bpf/libbpf.map | 16 ++++++++++++++
> > >  tools/lib/bpf/xsk.c      | 24 +++++++++++++++++++++
> > >  tools/lib/bpf/xsk.h      | 45 +++++++++++++++++++++++-----------------
> > >  3 files changed, 66 insertions(+), 19 deletions(-)
> > >
> >
> > [...]