bpf tools: Read eBPF object from buffer

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>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-7-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9e446081fb1c4ca7c433aeb6dfb750971811540c..36dfbc1dfa779c081a7151fb5283d00acbab197b 100644 (file)
--- 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 ec3301ceeb85e1704e75388ada5bd15863c10c05..dc966dd9fd75f7c9deac218f82eedab01121c790 100644 (file)
--- 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