[PATCH bpf-next] tools: libbpf: update extended attributes version of bpf_object__open()

[Anton Protopopov <a.s.protopopov@gmail.com>]

Update the bpf_object_open_attr structure and corresponding code so that the
bpf_object__open_xattr function could be used to open objects from buffers as
well as from files.  The reason for this change is that the existing
bpf_object__open_buffer function doesn't provide a way to specify neither the
needs_kver nor flags parameters to the internal call to __bpf_object__open
which makes it inconvenient for loading BPF objects which doesn't require a
kernel version.

Two new fields, obj_buf and obj_buf_sz, were added to the structure, and the
file field was union'ed with obj_name so that one can open an object like this:

    struct bpf_object_open_attr attr = {
        .obj_name   = name,
        .obj_buf    = obj_buf,
        .obj_buf_sz = obj_buf_sz,
        .prog_type  = BPF_PROG_TYPE_UNSPEC,
    };
    return bpf_object__open_xattr(&attr);

while still being able to use the file semantics:

    struct bpf_object_open_attr attr = {
        .file       = path,
        .prog_type  = BPF_PROG_TYPE_UNSPEC,
    };
    return bpf_object__open_xattr(&attr);

Another thing to note is that since the commit c034a177d3c8 ("bpf: bpftool, add
flag to allow non-compat map definitions") which introduced a MAPS_RELAX_COMPAT
flag to load objects with non-compat map definitions, bpf_object__open_buffer
was called with this flag enabled (it was passed as the boolean true value in
flags argument to __bpf_object__open).  The default behaviour for all open
functions is to clear this flag and this patch changes bpf_object__open_buffer
to clears this flag.  It can be enabled, if needed, by opening an object from
buffer using __bpf_object__open_xattr.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
---
 tools/lib/bpf/libbpf.c | 45 ++++++++++++++++++++++++++----------------
 tools/lib/bpf/libbpf.h |  7 ++++++-
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2233f919dd88..7c8054afd901 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3630,13 +3630,31 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
 struct bpf_object *__bpf_object__open_xattr(struct bpf_object_open_attr *attr,
 					    int flags)
 {
+	char tmp_name[64];
+
 	/* param validation */
-	if (!attr->file)
+	if (!attr)
 		return NULL;
 
-	pr_debug("loading %s\n", attr->file);
+	if (attr->obj_buf) {
+		if (attr->obj_buf_sz <= 0)
+			return NULL;
+		if (!attr->file) {
+			snprintf(tmp_name, sizeof(tmp_name), "%lx-%lx",
+				 (unsigned long)attr->obj_buf,
+				 (unsigned long)attr->obj_buf_sz);
+			attr->obj_name = tmp_name;
+		}
+		pr_debug("loading object '%s' from buffer\n", attr->obj_name);
+	} else if (!attr->file) {
+		return NULL;
+	} else {
+		attr->obj_buf_sz = 0;
 
-	return __bpf_object__open(attr->file, NULL, 0,
+		pr_debug("loading object file '%s'\n", attr->file);
+	}
+
+	return __bpf_object__open(attr->file, attr->obj_buf, attr->obj_buf_sz,
 				  bpf_prog_type__needs_kver(attr->prog_type),
 				  flags);
 }
@@ -3660,21 +3678,14 @@ struct bpf_object *bpf_object__open_buffer(void *obj_buf,
 					   size_t obj_buf_sz,
 					   const char *name)
 {
-	char tmp_name[64];
-
-	/* param validation */
-	if (!obj_buf || obj_buf_sz <= 0)
-		return NULL;
-
-	if (!name) {
-		snprintf(tmp_name, sizeof(tmp_name), "%lx-%lx",
-			 (unsigned long)obj_buf,
-			 (unsigned long)obj_buf_sz);
-		name = tmp_name;
-	}
-	pr_debug("loading object '%s' from buffer\n", name);
+	struct bpf_object_open_attr attr = {
+		.obj_name	= name,
+		.obj_buf	= obj_buf,
+		.obj_buf_sz	= obj_buf_sz,
+		.prog_type	= BPF_PROG_TYPE_UNSPEC,
+	};
 
-	return __bpf_object__open(name, obj_buf, obj_buf_sz, true, true);
+	return bpf_object__open_xattr(&attr);
 }
 
 int bpf_object__unload(struct bpf_object *obj)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index e8f70977d137..634f278578dd 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -63,8 +63,13 @@ LIBBPF_API libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn);
 struct bpf_object;
 
 struct bpf_object_open_attr {
-	const char *file;
+	union {
+		const char *file;
+		const char *obj_name;
+	};
 	enum bpf_prog_type prog_type;
+	void *obj_buf;
+	size_t obj_buf_sz;
 };
 
 LIBBPF_API struct bpf_object *bpf_object__open(const char *path);
-- 
2.19.1