[v3,bpf-next,1/7] bpf: add a __btf_get_by_fd helper

Commit Message

Anton Protopopov Nov. 29, 2024, 1:28 p.m. UTC

Add a new helper to get a pointer to a struct btf from a file
descriptor. This helper doesn't increase a refcnt. Add a comment
explaining this and pointing to a corresponding function which
does take a reference.

Signed-off-by: Anton Protopopov <[e-mail]>
---
 include/linux/bpf.h | 17 +++++++++++++++++
 include/linux/btf.h |  2 ++
 kernel/bpf/btf.c    | 13 ++++---------
 3 files changed, 23 insertions(+), 9 deletions(-)

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 3ace0d6227e3..fcb4ecd9d1fd 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2294,6 +2294,14 @@  void __bpf_obj_drop_impl(void *p, const struct btf_record *rec, bool percpu);
 struct bpf_map *bpf_map_get(u32 ufd);
 struct bpf_map *bpf_map_get_with_uref(u32 ufd);
 
+/*
+ * The __bpf_map_get() and __btf_get_by_fd() functions parse a file
+ * descriptor and return a corresponding map or btf object.
+ * Their names are double underscored to emphasize the fact that they
+ * do not increase refcnt. To also increase refcnt use corresponding
+ * bpf_map_get() and btf_get_by_fd() functions.
+ */
+
 static inline struct bpf_map *__bpf_map_get(struct fd f)
 {
 	if (fd_empty(f))
@@ -2303,6 +2311,15 @@  static inline struct bpf_map *__bpf_map_get(struct fd f)
 	return fd_file(f)->private_data;
 }
 
+static inline struct btf *__btf_get_by_fd(struct fd f)
+{
+	if (fd_empty(f))
+		return ERR_PTR(-EBADF);
+	if (unlikely(fd_file(f)->f_op != &btf_fops))
+		return ERR_PTR(-EINVAL);
+	return fd_file(f)->private_data;
+}
+
 void bpf_map_inc(struct bpf_map *map);
 void bpf_map_inc_with_uref(struct bpf_map *map);
 struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref);
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 4214e76c9168..69159e649675 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -4,6 +4,7 @@ 
 #ifndef _LINUX_BTF_H
 #define _LINUX_BTF_H 1
 
+#include <linux/file.h>
 #include <linux/types.h>
 #include <linux/bpfptr.h>
 #include <linux/bsearch.h>
@@ -143,6 +144,7 @@  void btf_get(struct btf *btf);
 void btf_put(struct btf *btf);
 const struct btf_header *btf_header(const struct btf *btf);
 int btf_new_fd(const union bpf_attr *attr, bpfptr_t uattr, u32 uattr_sz);
+
 struct btf *btf_get_by_fd(int fd);
 int btf_get_info_by_fd(const struct btf *btf,
 		       const union bpf_attr *attr,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index e7a59e6462a9..ad5310fa1d3b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7743,17 +7743,12 @@  int btf_new_fd(const union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 
 struct btf *btf_get_by_fd(int fd)
 {
-	struct btf *btf;
 	CLASS(fd, f)(fd);
+	struct btf *btf;
 
-	if (fd_empty(f))
-		return ERR_PTR(-EBADF);
-
-	if (fd_file(f)->f_op != &btf_fops)
-		return ERR_PTR(-EINVAL);
-
-	btf = fd_file(f)->private_data;
-	refcount_inc(&btf->refcnt);
+	btf = __btf_get_by_fd(f);
+	if (!IS_ERR(btf))
+		refcount_inc(&btf->refcnt);
 
 	return btf;
 }