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    Subject[PATCH] libbpf: Deprecate bpf_objects_list
    Date
    From: Joe Burton <jevburton@google.com>

    Add a flag to `enum libbpf_strict_mode' to disable the global
    `bpf_objects_list', preventing race conditions when concurrent threads
    call bpf_object__open() or bpf_object__close().

    bpf_object__next() will return NULL if this option is set.

    Callers may achieve the same workflow by tracking bpf_objects in
    application code.

    [0] Closes: https://github.com/libbpf/libbpf/issues/293

    Signed-off-by: Joe Burton <jevburton@google.com>
    ---
    tools/lib/bpf/libbpf.c | 8 +++++++-
    tools/lib/bpf/libbpf.h | 3 ++-
    tools/lib/bpf/libbpf_legacy.h | 6 ++++++
    3 files changed, 15 insertions(+), 2 deletions(-)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index 2fbed2d4a645..59d39ce9f375 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -1148,6 +1148,7 @@ static struct bpf_object *bpf_object__new(const char *path,
    size_t obj_buf_sz,
    const char *obj_name)
    {
    + bool strict = (libbpf_mode & LIBBPF_STRICT_NO_OBJECT_LIST);
    struct bpf_object *obj;
    char *end;

    @@ -1188,7 +1189,8 @@ static struct bpf_object *bpf_object__new(const char *path,
    obj->loaded = false;

    INIT_LIST_HEAD(&obj->list);
    - list_add(&obj->list, &bpf_objects_list);
    + if (!strict)
    + list_add(&obj->list, &bpf_objects_list);
    return obj;
    }

    @@ -7935,6 +7937,10 @@ struct bpf_object *
    bpf_object__next(struct bpf_object *prev)
    {
    struct bpf_object *next;
    + bool strict = (libbpf_mode & LIBBPF_STRICT_NO_OBJECT_LIST);
    +
    + if (strict)
    + return NULL;

    if (!prev)
    next = list_first_entry(&bpf_objects_list,
    diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
    index e1900819bfab..defabdbe7760 100644
    --- a/tools/lib/bpf/libbpf.h
    +++ b/tools/lib/bpf/libbpf.h
    @@ -168,7 +168,8 @@ LIBBPF_API struct bpf_program *
    bpf_object__find_program_by_name(const struct bpf_object *obj,
    const char *name);

    -LIBBPF_API struct bpf_object *bpf_object__next(struct bpf_object *prev);
    +LIBBPF_API LIBBPF_DEPRECATED_SINCE(0, 7, "track bpf_objects in application code instead")
    +struct bpf_object *bpf_object__next(struct bpf_object *prev);
    #define bpf_object__for_each_safe(pos, tmp) \
    for ((pos) = bpf_object__next(NULL), \
    (tmp) = bpf_object__next(pos); \
    diff --git a/tools/lib/bpf/libbpf_legacy.h b/tools/lib/bpf/libbpf_legacy.h
    index 29ccafab11a8..5ba5c9beccfa 100644
    --- a/tools/lib/bpf/libbpf_legacy.h
    +++ b/tools/lib/bpf/libbpf_legacy.h
    @@ -57,6 +57,12 @@ enum libbpf_strict_mode {
    * function name instead of section name.
    */
    LIBBPF_STRICT_SEC_NAME = 0x04,
    + /*
    + * Disable the global 'bpf_objects_list'. Maintaining this list adds
    + * a race condition to bpf_object__open() and bpf_object__close().
    + * Clients can maintain it on their own if it is valuable for them.
    + */
    + LIBBPF_STRICT_NO_OBJECT_LIST = 0x08,

    __LIBBPF_STRICT_LAST,
    };
    --
    2.33.0.1079.g6e70778dc9-goog
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