bpf: Introduce bpf_sysctl_get_name helper

Add bpf_sysctl_get_name() helper to copy sysctl name (/proc/sys/ entry)
into provided by BPF_PROG_TYPE_CGROUP_SYSCTL program buffer.

By default full name (w/o /proc/sys/) is copied, e.g. "net/ipv4/tcp_mem".

If BPF_F_SYSCTL_BASE_NAME flag is set, only base name will be copied,
e.g. "tcp_mem".

Documentation for the new helper is provided in bpf.h UAPI.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 21 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index cc2a2466d5f3..9c8a2f3ccb9b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2506,6 +2506,22 @@ union bpf_attr {
  *      Return
  *              0 if iph and th are a valid SYN cookie ACK, or a negative error
  *              otherwise.
+ *
+ * int bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t buf_len, u64 flags)
+ *      Description
+ *              Get name of sysctl in /proc/sys/ and copy it into provided by
+ *              program buffer *buf* of size *buf_len*.
+ *
+ *              The buffer is always NUL terminated, unless it's zero-sized.
+ *
+ *              If *flags* is zero, full name (e.g. "net/ipv4/tcp_mem") is
+ *              copied. Use **BPF_F_SYSCTL_BASE_NAME** flag to copy base name
+ *              only (e.g. "tcp_mem").
+ *      Return
+ *              Number of character copied (not including the trailing NUL).
+ *
+ *              **-E2BIG** if the buffer wasn't big enough (*buf* will contain
+ *              truncated name in this case).
  */
 #define __BPF_FUNC_MAPPER(FN)           \
         FN(unspec),                     \
@@ -2608,7 +2624,8 @@ union bpf_attr {
         FN(skb_ecn_set_ce),             \
         FN(get_listener_sock),          \
         FN(skc_lookup_tcp),             \
-        FN(tcp_check_syncookie),
+        FN(tcp_check_syncookie),        \
+        FN(sysctl_get_name),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -2681,6 +2698,9 @@ enum bpf_func_id {
                                           BPF_ADJ_ROOM_ENCAP_L2_MASK) \
                                          << BPF_ADJ_ROOM_ENCAP_L2_SHIFT)
 
+/* BPF_FUNC_sysctl_get_name flags. */
+#define BPF_F_SYSCTL_BASE_NAME          (1ULL << 0)
+
 /* Mode for BPF_FUNC_skb_adjust_room helper. */
 enum bpf_adj_room_mode {
         BPF_ADJ_ROOM_NET,