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bpf: Add a __btf_get_by_fd helper

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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 <aspsk@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241213130934.1087929-2-aspsk@isovalent.com
This commit is contained in:
Anton Protopopov 2024-12-13 13:09:28 +00:00 committed by Andrii Nakryiko
parent 6a10d2d361
commit 4e885fab71
2 changed files with 20 additions and 8 deletions
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17
include/linux/bpf.h
View File

@ -2301,6 +2301,14 @@ 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))
@ -2310,6 +2318,15 @@ 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);

11
kernel/bpf/btf.c
View File

@ -7746,14 +7746,9 @@ struct btf *btf_get_by_fd(int fd)
struct btf *btf;
CLASS(fd, f)(fd);
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;
}