Re: [PATCH bpf-next v3] bpf: add new helper fd2path for mapping a file descriptor to a pathname

index 2c2c29b49845..d73314a7e674 100644

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1082,6 +1082,7 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
 extern const struct bpf_func_proto bpf_strtol_proto;
 extern const struct bpf_func_proto bpf_strtoul_proto;
 extern const struct bpf_func_proto bpf_tcp_sock_proto;
+extern const struct bpf_func_proto bpf_fd2path_proto;

 /* Shared helpers among cBPF and eBPF. */
 void bpf_user_rnd_init_once(void);

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4af8b0819a32..fdb37740951f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -2773,6 +2773,15 @@ union bpf_attr {
  *
  * 		This helper is similar to **bpf_perf_event_output**\ () but
  * 		restricted to raw_tracepoint bpf programs.
+ *
+ * int bpf_fd2path(char *path, u32 size, int fd)
+ *	Description
+ *		Get **file** atrribute from the current task by *fd*, then call
+ *		**d_path** to get it's absolute path and copy it as string into
+ *		*path* of *size*. The **path** also support pseudo filesystems
+ *		(whether or not it can be mounted). The *size* must be strictly
+ *		positive. On success, the helper makes sure that the *path* is
+ *		NUL-terminated. On failure, it is filled with zeroes.
  * 	Return
  * 		0 on success, or a negative error in case of failure.

  */

@@ -2888,7 +2897,8 @@ union bpf_attr {
 	FN(sk_storage_delete),		\
 	FN(send_signal),		\
 	FN(tcp_gen_syncookie),		\
-	FN(skb_output),
+	FN(skb_output),			\
+	FN(fd2path),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 673f5d40a93e..6b44ed804280 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c

@@ -2079,6 +2079,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
 const struct bpf_func_proto bpf_get_current_comm_proto __weak;
 const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
 const struct bpf_func_proto bpf_get_local_storage_proto __weak;
+const struct bpf_func_proto bpf_fd2path_proto __weak;

 const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
 {

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5e28718928ca..8e6b4189a456 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c

@@ -487,3 +487,39 @@ const struct bpf_func_proto bpf_strtoul_proto = {
 	.arg4_type	= ARG_PTR_TO_LONG,
 };
 #endif
+
+BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd)
+{
+	struct fd f;
+	char *p;
+	int ret = -EINVAL;
+
+	f = fdget_raw(fd);

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index c3240898cc44..26f65abdb249 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -735,6 +735,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 #endif
 	case BPF_FUNC_send_signal:
 		return &bpf_send_signal_proto;
+	case BPF_FUNC_fd2path:
+		return &bpf_fd2path_proto;
 	default:
 		return NULL;
 	}

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 4af8b0819a32..fdb37740951f 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h

@@ -2773,6 +2773,15 @@ union bpf_attr {
  *
  * 		This helper is similar to **bpf_perf_event_output**\ () but
  * 		restricted to raw_tracepoint bpf programs.
+ *
+ * int bpf_fd2path(char *path, u32 size, int fd)
+ *	Description
+ *		Get **file** atrribute from the current task by *fd*, then call
+ *		**d_path** to get it's absolute path and copy it as string into
+ *		*path* of *size*. The **path** also support pseudo filesystems
+ *		(whether or not it can be mounted). The *size* must be strictly
+ *		positive. On success, the helper makes sure that the *path* is
+ *		NUL-terminated. On failure, it is filled with zeroes.
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  */

@@ -2888,7 +2897,8 @@ union bpf_attr {
 	FN(sk_storage_delete),		\
 	FN(send_signal),		\
 	FN(tcp_gen_syncookie),		\
-	FN(skb_output),
+	FN(skb_output),			\
+	FN(fd2path),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 933f39381039..32883cca7ea7 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile