On 03/08/2021 19.10, Kishen Maloor wrote:
This change adds userspace support for SO_TXTIME in AF_XDP
to include a specific TXTIME (aka "Launch Time")
with XDP frames issued from userspace XDP applications.
The userspace API has been expanded with two helper functons:
- int xsk_socket__enable_so_txtime(struct xsk_socket *xsk, bool enable)
Sets the SO_TXTIME option on the AF_XDP socket (using setsockopt()).
- void xsk_umem__set_md_txtime(void *umem_area, __u64 chunkAddr,
__s64 txtime)
Packages the application supplied TXTIME into struct xdp_user_tx_metadata:
struct xdp_user_tx_metadata {
Struct name is important and becomes UAPI. I'm not 100% convinced this
is a good name.
For BPF programs libbpf can at load-time lookup the 'btf_id' via:
btf_id = bpf_core_type_id_kernel(struct xdp_user_tx_metadata);
Example see[1]
[1] https://github.com/xdp-project/bpf-examples/commit/2390b4b11079
I know this is AF_XDP userspace, but I hope Andrii can help guide us
howto expose the bpf_core_type_id_kernel() API via libbpf, to be used by
the AF_XDP userspace program.
__u64 timestamp;
__u32 md_valid;
__u32 btf_id;
};
I assume this struct is intended to be BTF "described".
Struct member *names* are very important for BTF. (E.g. see how
'spinlock' have special meaning and is matched internally by kernel).
The member name 'timestamp' seems too generic. This is a very specific
'LaunchTime' feature, which could be reflected in the name.
Later it looks like you are encoding the "type" in md_valid, which I
guess it is needed as timestamps can have different "types".
E.g. some of the clockid_t types from clock_gettime(2):
CLOCK_REALTIME
CLOCK_TAI
CLOCK_MONOTONIC
CLOCK_BOOTTIME
Which of these timestamp does XDP_METADATA_USER_TX_TIMESTAMP represent?
Or what timestamp type is the expected one?
In principle we could name the member 'Launch_Time_CLOCK_TAI' to encoded
the clockid_t type in the name, but I think that would be too much (and
require too advanced BTF helpers to extract type, having a clock_type
member is easier to understand/consume from C).
and stores it in the XDP metadata area, which precedes the XDP frame.
Signed-off-by: Kishen Maloor <kishen.maloor@xxxxxxxxx>
---
tools/include/uapi/linux/if_xdp.h | 2 ++
tools/include/uapi/linux/xdp_md_std.h | 14 ++++++++++++++
tools/lib/bpf/xsk.h | 27 ++++++++++++++++++++++++++-
3 files changed, 42 insertions(+), 1 deletion(-)
create mode 100644 tools/include/uapi/linux/xdp_md_std.h
diff --git a/tools/include/uapi/linux/if_xdp.h b/tools/include/uapi/linux/if_xdp.h
index a78a8096f4ce..31f81f82ed86 100644
--- a/tools/include/uapi/linux/if_xdp.h
+++ b/tools/include/uapi/linux/if_xdp.h
@@ -106,6 +106,8 @@ struct xdp_desc {
__u32 options;
};
+#define XDP_DESC_OPTION_METADATA (1 << 0)
+
/* UMEM descriptor is __u64 */
#endif /* _LINUX_IF_XDP_H */
diff --git a/tools/include/uapi/linux/xdp_md_std.h b/tools/include/uapi/linux/xdp_md_std.h
new file mode 100644
index 000000000000..f00996a61639
--- /dev/null
+++ b/tools/include/uapi/linux/xdp_md_std.h
@@ -0,0 +1,14 @@
+#ifndef _UAPI_LINUX_XDP_MD_STD_H
+#define _UAPI_LINUX_XDP_MD_STD_H
+
+#include <linux/types.h>
+
+#define XDP_METADATA_USER_TX_TIMESTAMP 0x1
+
+struct xdp_user_tx_metadata {
+ __u64 timestamp;
+ __u32 md_valid;
+ __u32 btf_id;
+};
+
+#endif /* _UAPI_LINUX_XDP_MD_STD_H */
diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 01c12dca9c10..1b52ffe1c9a3 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -16,7 +16,8 @@
#include <stdint.h>
#include <stdbool.h>
#include <linux/if_xdp.h>
-
+#include <linux/xdp_md_std.h>
+#include <errno.h>
#include "libbpf.h"
#ifdef __cplusplus
@@ -248,6 +249,30 @@ static inline __u64 xsk_umem__add_offset_to_addr(__u64 addr)
LIBBPF_API int xsk_umem__fd(const struct xsk_umem *umem);
LIBBPF_API int xsk_socket__fd(const struct xsk_socket *xsk);
+/* Helpers for SO_TXTIME */
+
+static inline void xsk_umem__set_md_txtime(void *umem_area, __u64 addr, __s64 txtime)
+{
+ struct xdp_user_tx_metadata *md;
+
+ md = (struct xdp_user_tx_metadata *)&((char *)umem_area)[addr];
+
+ md->timestamp = txtime;
+ md->md_valid |= XDP_METADATA_USER_TX_TIMESTAMP;
Is this encoding the "type" of the timestamp?
I don't see the btf_id being updated. Does that happen in another patch?
As I note above we are current;y lacking an libbpf equivalent
bpf_core_type_id_kernel() lookup function in userspace.
+}
+
+static inline int xsk_socket__enable_so_txtime(struct xsk_socket *xsk, bool enable)
+{
+ unsigned int val = (enable) ? 1 : 0;
+ int err;
+
+ err = setsockopt(xsk_socket__fd(xsk), SOL_XDP, SO_TXTIME, &val, sizeof(val));
+
+ if (err)
+ return -errno;
+ return 0;
+}
+
#define XSK_RING_CONS__DEFAULT_NUM_DESCS 2048
#define XSK_RING_PROD__DEFAULT_NUM_DESCS 2048
#define XSK_UMEM__DEFAULT_FRAME_SHIFT 12 /* 4096 bytes */
