[PATCH bpf-next v1 1/3] bpf: Add bpf_file_d_path helper

[Lin Yikai]

Add the "bpf_file_d_path" helper function
to retrieve the path from a struct file object.
But there is no need to include vmlinux.h
or reference the definition of struct file.

Additionally, update the bpf.h tools uapi header.

Signed-off-by: Lin Yikai <yikai.lin@xxxxxxxx>
---
 include/uapi/linux/bpf.h       | 20 ++++++++++++++++++++
 kernel/trace/bpf_trace.c       | 34 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h | 20 ++++++++++++++++++++
 3 files changed, 74 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 35bcf52dbc65..7e5cec61a877 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5792,6 +5792,25 @@ union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_file_d_path(void *file, char *dst, u32 size)
+ *	Description
+ *		Return full path for the given *file* object.
+ *
+ *		In order to solve issues where certain eBPF programs can not include
+ *		the definition of struct file or vmlinux.h
+ *		due to their complexity and conflicts on some operating system,
+ *		the variable *file* here is declared as type void*
+ *		instead of the traditional struct file*.
+ *		It will be forcibly converted into type struct file* later.
+ *
+ *		If the path is larger than *size*, then only *size*
+ *		bytes will be copied to *dst*
+ *
+ *	Return
+ *		On success, the strictly positive length of the string,
+ *		including the trailing NULL character. On error, a negative
+ *		value.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -6006,6 +6025,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(file_d_path, 212, ##ctx)			\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index cd098846e251..70fde7f20e97 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1257,6 +1257,38 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
 	.arg1_type	= ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_3(bpf_file_d_path, void *, file, char*, dst, u32, size)
+{
+	long len;
+	struct file copy;
+	char *ptr;
+
+	if (!size)
+		return 0;
+
+	len = copy_from_kernel_nofault(&copy, (struct file *)file, sizeof(struct file));
+	if (len < 0)
+		return len;
+
+	ptr = d_path(&(copy.f_path), dst, size);
+	if (IS_ERR(ptr)) {
+		len = PTR_ERR(ptr);
+	} else {
+		len = dst + size - ptr;
+		memmove(dst, ptr, len);
+	}
+	return len;
+}
+
+const struct bpf_func_proto bpf_file_d_path_proto = {
+	.func		= bpf_file_d_path,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_ANYTHING,
+	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg3_type	= ARG_CONST_SIZE_OR_ZERO,
+};
+
 #ifdef CONFIG_KEYS
 __bpf_kfunc_start_defs();
 
@@ -1629,6 +1661,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_find_vma_proto;
 	case BPF_FUNC_trace_vprintk:
 		return bpf_get_trace_vprintk_proto();
+	case BPF_FUNC_file_d_path:
+		return &bpf_file_d_path_proto;
 	default:
 		return bpf_base_func_proto(func_id, prog);
 	}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 35bcf52dbc65..7e5cec61a877 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5792,6 +5792,25 @@ union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_file_d_path(void *file, char *dst, u32 size)
+ *	Description
+ *		Return full path for the given *file* object.
+ *
+ *		In order to solve issues where certain eBPF programs can not include
+ *		the definition of struct file or vmlinux.h
+ *		due to their complexity and conflicts on some operating system,
+ *		the variable *file* here is declared as type void*
+ *		instead of the traditional struct file*.
+ *		It will be forcibly converted into type struct file* later.
+ *
+ *		If the path is larger than *size*, then only *size*
+ *		bytes will be copied to *dst*
+ *
+ *	Return
+ *		On success, the strictly positive length of the string,
+ *		including the trailing NULL character. On error, a negative
+ *		value.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -6006,6 +6025,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(file_d_path, 212, ##ctx)			\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
-- 
2.34.1