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    Subject[RFC PATCH v7 05/37] bpf tools: Read eBPF object from buffer
    Date
    To support dynamic compiling, this patch allows caller to pass a
    in-memory buffer to libbpf by bpf_object__open_buffer(). libbpf
    calls elf_memory() to open it as ELF object file.

    Because __bpf_object__open() collects all required data and won't need
    that buffer anymore, libbpf uses that buffer directly instead of clone
    a new buffer. Caller of libbpf can free that buffer or use it do other
    things after bpf_object__open_buffer() return.

    Signed-off-by: Wang Nan <wangnan0@huawei.com>
    ---
    tools/lib/bpf/libbpf.c | 62 ++++++++++++++++++++++++++++++++++++++++----------
    tools/lib/bpf/libbpf.h | 2 ++
    2 files changed, 52 insertions(+), 12 deletions(-)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index 197ab5e..8ba6ac6 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -84,6 +84,8 @@ struct bpf_object {
    */
    struct {
    int fd;
    + void *obj_buf;
    + size_t obj_buf_sz;
    Elf *elf;
    GElf_Ehdr ehdr;
    } efile;
    @@ -91,7 +93,9 @@ struct bpf_object {
    };
    #define obj_elf_valid(o) ((o)->efile.elf)

    -static struct bpf_object *bpf_object__new(const char *path)
    +static struct bpf_object *bpf_object__new(const char *path,
    + void *obj_buf,
    + size_t obj_buf_sz)
    {
    struct bpf_object *obj;

    @@ -103,6 +107,16 @@ static struct bpf_object *bpf_object__new(const char *path)

    strcpy(obj->path, path);
    obj->efile.fd = -1;
    +
    + /*
    + * Caller of this function should also calls
    + * bpf_object__elf_finish() after data collection to return
    + * obj_buf to user. If not, we should duplicate the buffer to
    + * avoid user freeing them before elf finish.
    + */
    + obj->efile.obj_buf = obj_buf;
    + obj->efile.obj_buf_sz = obj_buf_sz;
    +
    return obj;
    }

    @@ -116,6 +130,8 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
    obj->efile.elf = NULL;
    }
    zclose(obj->efile.fd);
    + obj->efile.obj_buf = NULL;
    + obj->efile.obj_buf_sz = 0;
    }

    static int bpf_object__elf_init(struct bpf_object *obj)
    @@ -128,16 +144,26 @@ static int bpf_object__elf_init(struct bpf_object *obj)
    return -EEXIST;
    }

    - obj->efile.fd = open(obj->path, O_RDONLY);
    - if (obj->efile.fd < 0) {
    - pr_warning("failed to open %s: %s\n", obj->path,
    - strerror(errno));
    - return -errno;
    + if (obj->efile.obj_buf_sz > 0) {
    + /*
    + * obj_buf should have been validated by
    + * bpf_object__open_buffer().
    + */
    + obj->efile.elf = elf_memory(obj->efile.obj_buf,
    + obj->efile.obj_buf_sz);
    + } else {
    + obj->efile.fd = open(obj->path, O_RDONLY);
    + if (obj->efile.fd < 0) {
    + pr_warning("failed to open %s: %s\n", obj->path,
    + strerror(errno));
    + return -errno;
    + }
    +
    + obj->efile.elf = elf_begin(obj->efile.fd,
    + LIBBPF_ELF_C_READ_MMAP,
    + NULL);
    }

    - obj->efile.elf = elf_begin(obj->efile.fd,
    - LIBBPF_ELF_C_READ_MMAP,
    - NULL);
    if (!obj->efile.elf) {
    pr_warning("failed to open %s as ELF file\n",
    obj->path);
    @@ -167,7 +193,7 @@ errout:
    }

    static struct bpf_object *
    -__bpf_object__open(const char *path)
    +__bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz)
    {
    struct bpf_object *obj;

    @@ -176,7 +202,7 @@ __bpf_object__open(const char *path)
    return NULL;
    }

    - obj = bpf_object__new(path);
    + obj = bpf_object__new(path, obj_buf, obj_buf_sz);
    if (!obj)
    return NULL;

    @@ -198,7 +224,19 @@ struct bpf_object *bpf_object__open(const char *path)

    pr_debug("loading %s\n", path);

    - return __bpf_object__open(path);
    + return __bpf_object__open(path, NULL, 0);
    +}
    +
    +struct bpf_object *bpf_object__open_buffer(void *obj_buf,
    + size_t obj_buf_sz)
    +{
    + /* param validation */
    + if (!obj_buf || obj_buf_sz <= 0)
    + return NULL;
    +
    + pr_debug("loading object from buffer\n");
    +
    + return __bpf_object__open("[buffer]", obj_buf, obj_buf_sz);
    }

    void bpf_object__close(struct bpf_object *obj)
    diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
    index ec3301c..dc966dd 100644
    --- a/tools/lib/bpf/libbpf.h
    +++ b/tools/lib/bpf/libbpf.h
    @@ -26,6 +26,8 @@ void libbpf_set_print(libbpf_print_fn_t warn,
    struct bpf_object;

    struct bpf_object *bpf_object__open(const char *path);
    +struct bpf_object *bpf_object__open_buffer(void *obj_buf,
    + size_t obj_buf_sz);
    void bpf_object__close(struct bpf_object *object);

    #endif
    --
    1.8.3.4


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