Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next

Pull networking updates from David Miller:
 "Here we go, another merge window full of networking and #ebpf changes:

   1) Snoop DHCPACKS in batman-adv to learn MAC/IP pairs in the DHCP
      range without dealing with floods of ARP traffic, from Linus
      Lüssing.

   2) Throttle buffered multicast packet transmission in mt76, from
      Felix Fietkau.

   3) Support adaptive interrupt moderation in ice, from Brett Creeley.

   4) A lot of struct_size conversions, from Gustavo A. R. Silva.

   5) Add peek/push/pop commands to bpftool, as well as bash completion,
      from Stanislav Fomichev.

   6) Optimize sk_msg_clone(), from Vakul Garg.

   7) Add SO_BINDTOIFINDEX, from David Herrmann.

   8) Be more conservative with local resends due to local congestion,
      from Yuchung Cheng.

   9) Allow vetoing of unsupported VXLAN FDBs, from Petr Machata.

  10) Add health buffer support to devlink, from Eran Ben Elisha.

  11) Add TXQ scheduling API to mac80211, from Toke Høiland-Jørgensen.

  12) Add statistics to basic packet scheduler filter, from Cong Wang.

  13) Add GRE tunnel support for mlxsw Spectrum-2, from Nir Dotan.

  14) Lots of new IP tunneling forwarding tests, also from Nir Dotan.

  15) Add 3ad stats to bonding, from Nikolay Aleksandrov.

  16) Lots of probing improvements for bpftool, from Quentin Monnet.

  17) Various nfp drive #ebpf JIT improvements from Jakub Kicinski.

  18) Allow #ebpf programs to access gso_segs from skb shared info, from
      Eric Dumazet.

  19) Add sock_diag support for AF_XDP sockets, from Björn Töpel.

  20) Support 22260 iwlwifi devices, from Luca Coelho.

  21) Use rbtree for ipv6 defragmentation, from Peter Oskolkov.

  22) Add JMP32 instruction class support to #ebpf, from Jiong Wang.

  23) Add spinlock support to #ebpf, from Alexei Starovoitov.

  24) Support 256-bit keys and TLS 1.3 in ktls, from Dave Watson.

  25) Add device infomation API to devlink, from Jakub Kicinski.

  26) Add new timestamping socket options which are y2038 safe, from
      Deepa Dinamani.

  27) Add RX checksum offloading for various sh_eth chips, from Sergei
      Shtylyov.

  28) Flow offload infrastructure, from Pablo Neira Ayuso.

  29) Numerous cleanups, improvements, and bug fixes to the PHY layer
      and many drivers from Heiner Kallweit.

  30) Lots of changes to try and make packet scheduler classifiers run
      lockless as much as possible, from Vlad Buslov.

  31) Support BCM957504 chip in bnxt_en driver, from Erik Burrows.

  32) Add concurrency tests to tc-tests infrastructure, from Vlad
      Buslov.

  33) Add hwmon support to aquantia, from Heiner Kallweit.

  34) Allow 64-bit values for SO_MAX_PACING_RATE, from Eric Dumazet.

  And I would be remiss if I didn't thank the various major networking
  subsystem maintainers for integrating much of this work before I even
  saw it. Alexei Starovoitov, Daniel Borkmann, Pablo Neira Ayuso,
  Johannes Berg, Kalle Valo, and many others. Thank you!"

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next: (2207 commits)
  net/sched: avoid unused-label warning
  net: ignore sysctl_devconf_inherit_init_net without SYSCTL
  phy: mdio-mux: fix Kconfig dependencies
  net: phy: use phy_modify_mmd_changed in genphy_c45_an_config_aneg
  net: dsa: mv88e6xxx: add call to mv88e6xxx_ports_cmode_init to probe for new DSA framework
  selftest/net: Remove duplicate header
  sky2: Disable MSI on Dell Inspiron 1545 and Gateway P-79
  net/mlx5e: Update tx reporter status in case channels were successfully opened
  devlink: Add support for direct reporter health state update
  devlink: Update reporter state to error even if recover aborted
  sctp: call iov_iter_revert() after sending ABORT
  team: Free BPF filter when unregistering netdev
  ip6mr: Do not call __IP6_INC_STATS() from preemptible context
  isdn: mISDN: Fix potential NULL pointer dereference of kzalloc
  net: dsa: mv88e6xxx: support in-band signalling on SGMII ports with external PHYs
  cxgb4/chtls: Prefix adapter flags with CXGB4
  net-sysfs: Switch to bitmap_zalloc()
  mellanox: Switch to bitmap_zalloc()
  bpf: add test cases for non-pointer sanitiation logic
  mlxsw: i2c: Extend initialization by querying resources data
  ...

47 files changed, 2741 insertions, 689 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 858b6c0b9a15..bcf2cd519d1e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -461,6 +461,11 @@
 			possible to determine what the correct size should be.
 			This option provides an override for these situations.
 
+	carrier_timeout=
+			[NET] Specifies amount of time (in seconds) that
+			the kernel should wait for a network carrier. By default
+			it waits 120 seconds.
+
 	ca_keys=	[KEYS] This parameter identifies a specific key(s) on
 			the system trusted keyring to be used for certificate
 			trust validation.
diff --git a/Documentation/bpf/bpf_design_QA.rst b/Documentation/bpf/bpf_design_QA.rst
index 7cc9e368c1e9..10453c627135 100644
--- a/Documentation/bpf/bpf_design_QA.rst
+++ b/Documentation/bpf/bpf_design_QA.rst
@@ -36,27 +36,27 @@ consideration important quirks of other architectures) and
 defines calling convention that is compatible with C calling
 convention of the linux kernel on those architectures.
 
-Q: can multiple return values be supported in the future?
+Q: Can multiple return values be supported in the future?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A: NO. BPF allows only register R0 to be used as return value.
 
-Q: can more than 5 function arguments be supported in the future?
+Q: Can more than 5 function arguments be supported in the future?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A: NO. BPF calling convention only allows registers R1-R5 to be used
 as arguments. BPF is not a standalone instruction set.
 (unlike x64 ISA that allows msft, cdecl and other conventions)
 
-Q: can BPF programs access instruction pointer or return address?
+Q: Can BPF programs access instruction pointer or return address?
 -----------------------------------------------------------------
 A: NO.
 
-Q: can BPF programs access stack pointer ?
+Q: Can BPF programs access stack pointer ?
 ------------------------------------------
 A: NO.
 
 Only frame pointer (register R10) is accessible.
 From compiler point of view it's necessary to have stack pointer.
-For example LLVM defines register R11 as stack pointer in its
+For example, LLVM defines register R11 as stack pointer in its
 BPF backend, but it makes sure that generated code never uses it.
 
 Q: Does C-calling convention diminishes possible use cases?
@@ -66,8 +66,8 @@ A: YES.
 BPF design forces addition of major functionality in the form
 of kernel helper functions and kernel objects like BPF maps with
 seamless interoperability between them. It lets kernel call into
-BPF programs and programs call kernel helpers with zero overhead.
-As all of them were native C code. That is particularly the case
+BPF programs and programs call kernel helpers with zero overhead,
+as all of them were native C code. That is particularly the case
 for JITed BPF programs that are indistinguishable from
 native kernel C code.
 
@@ -75,9 +75,9 @@ Q: Does it mean that 'innovative' extensions to BPF code are disallowed?
 ------------------------------------------------------------------------
 A: Soft yes.
 
-At least for now until BPF core has support for
+At least for now, until BPF core has support for
 bpf-to-bpf calls, indirect calls, loops, global variables,
-jump tables, read only sections and all other normal constructs
+jump tables, read-only sections, and all other normal constructs
 that C code can produce.
 
 Q: Can loops be supported in a safe way?
@@ -109,16 +109,16 @@ For example why BPF_JNE and other compare and jumps are not cpu-like?
 A: This was necessary to avoid introducing flags into ISA which are
 impossible to make generic and efficient across CPU architectures.
 
-Q: why BPF_DIV instruction doesn't map to x64 div?
+Q: Why BPF_DIV instruction doesn't map to x64 div?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A: Because if we picked one-to-one relationship to x64 it would have made
 it more complicated to support on arm64 and other archs. Also it
 needs div-by-zero runtime check.
 
-Q: why there is no BPF_SDIV for signed divide operation?
+Q: Why there is no BPF_SDIV for signed divide operation?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A: Because it would be rarely used. llvm errors in such case and
-prints a suggestion to use unsigned divide instead
+prints a suggestion to use unsigned divide instead.
 
 Q: Why BPF has implicit prologue and epilogue?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
new file mode 100644
index 000000000000..9a60a5d60e38
--- /dev/null
+++ b/Documentation/bpf/btf.rst
@@ -0,0 +1,848 @@
+=====================
+BPF Type Format (BTF)
+=====================
+
+1. Introduction
+***************
+
+BTF (BPF Type Format) is the metadata format which encodes the debug info
+related to BPF program/map. The name BTF was used initially to describe data
+types. The BTF was later extended to include function info for defined
+subroutines, and line info for source/line information.
+
+The debug info is used for map pretty print, function signature, etc. The
+function signature enables better bpf program/function kernel symbol. The line
+info helps generate source annotated translated byte code, jited code and
+verifier log.
+
+The BTF specification contains two parts,
+  * BTF kernel API
+  * BTF ELF file format
+
+The kernel API is the contract between user space and kernel. The kernel
+verifies the BTF info before using it. The ELF file format is a user space
+contract between ELF file and libbpf loader.
+
+The type and string sections are part of the BTF kernel API, describing the
+debug info (mostly types related) referenced by the bpf program. These two
+sections are discussed in details in :ref:`BTF_Type_String`.
+
+.. _BTF_Type_String:
+
+2. BTF Type and String Encoding
+*******************************
+
+The file ``include/uapi/linux/btf.h`` provides high-level definition of how
+types/strings are encoded.
+
+The beginning of data blob must be::
+
+    struct btf_header {
+        __u16   magic;
+        __u8    version;
+        __u8    flags;
+        __u32   hdr_len;
+
+        /* All offsets are in bytes relative to the end of this header */
+        __u32   type_off;       /* offset of type section       */
+        __u32   type_len;       /* length of type section       */
+        __u32   str_off;        /* offset of string section     */
+        __u32   str_len;        /* length of string section     */
+    };
+
+The magic is ``0xeB9F``, which has different encoding for big and little
+endian systems, and can be used to test whether BTF is generated for big- or
+little-endian target. The ``btf_header`` is designed to be extensible with
+``hdr_len`` equal to ``sizeof(struct btf_header)`` when a data blob is
+generated.
+
+2.1 String Encoding
+===================
+
+The first string in the string section must be a null string. The rest of
+string table is a concatenation of other null-terminated strings.
+
+2.2 Type Encoding
+=================
+
+The type id ``0`` is reserved for ``void`` type. The type section is parsed
+sequentially and type id is assigned to each recognized type starting from id
+``1``. Currently, the following types are supported::
+
+    #define BTF_KIND_INT            1       /* Integer      */
+    #define BTF_KIND_PTR            2       /* Pointer      */
+    #define BTF_KIND_ARRAY          3       /* Array        */
+    #define BTF_KIND_STRUCT         4       /* Struct       */
+    #define BTF_KIND_UNION          5       /* Union        */
+    #define BTF_KIND_ENUM           6       /* Enumeration  */
+    #define BTF_KIND_FWD            7       /* Forward      */
+    #define BTF_KIND_TYPEDEF        8       /* Typedef      */
+    #define BTF_KIND_VOLATILE       9       /* Volatile     */
+    #define BTF_KIND_CONST          10      /* Const        */
+    #define BTF_KIND_RESTRICT       11      /* Restrict     */
+    #define BTF_KIND_FUNC           12      /* Function     */
+    #define BTF_KIND_FUNC_PROTO     13      /* Function Proto       */
+
+Note that the type section encodes debug info, not just pure types.
+``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
+
+Each type contains the following common data::
+
+    struct btf_type {
+        __u32 name_off;
+        /* "info" bits arrangement
+         * bits  0-15: vlen (e.g. # of struct's members)
+         * bits 16-23: unused
+         * bits 24-27: kind (e.g. int, ptr, array...etc)
+         * bits 28-30: unused
+         * bit     31: kind_flag, currently used by
+         *             struct, union and fwd
+         */
+        __u32 info;
+        /* "size" is used by INT, ENUM, STRUCT and UNION.
+         * "size" tells the size of the type it is describing.
+         *
+         * "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
+         * FUNC and FUNC_PROTO.
+         * "type" is a type_id referring to another type.
+         */
+        union {
+                __u32 size;
+                __u32 type;
+        };
+    };
+
+For certain kinds, the common data are followed by kind-specific data. The
+``name_off`` in ``struct btf_type`` specifies the offset in the string table.
+The following sections detail encoding of each kind.
+
+2.2.1 BTF_KIND_INT
+~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+ * ``name_off``: any valid offset
+ * ``info.kind_flag``: 0
+ * ``info.kind``: BTF_KIND_INT
+ * ``info.vlen``: 0
+ * ``size``: the size of the int type in bytes.
+
+``btf_type`` is followed by a ``u32`` with the following bits arrangement::
+
+  #define BTF_INT_ENCODING(VAL)   (((VAL) & 0x0f000000) >> 24)
+  #define BTF_INT_OFFSET(VAL)     (((VAL  & 0x00ff0000)) >> 16)
+  #define BTF_INT_BITS(VAL)       ((VAL)  & 0x000000ff)
+
+The ``BTF_INT_ENCODING`` has the following attributes::
+
+  #define BTF_INT_SIGNED  (1 << 0)
+  #define BTF_INT_CHAR    (1 << 1)
+  #define BTF_INT_BOOL    (1 << 2)
+
+The ``BTF_INT_ENCODING()`` provides extra information: signedness, char, or
+bool, for the int type. The char and bool encoding are mostly useful for
+pretty print. At most one encoding can be specified for the int type.
+
+The ``BTF_INT_BITS()`` specifies the number of actual bits held by this int
+type. For example, a 4-bit bitfield encodes ``BTF_INT_BITS()`` equals to 4.
+The ``btf_type.size * 8`` must be equal to or greater than ``BTF_INT_BITS()``
+for the type. The maximum value of ``BTF_INT_BITS()`` is 128.
+
+The ``BTF_INT_OFFSET()`` specifies the starting bit offset to calculate values
+for this int. For example, a bitfield struct member has: * btf member bit
+offset 100 from the start of the structure, * btf member pointing to an int
+type, * the int type has ``BTF_INT_OFFSET() = 2`` and ``BTF_INT_BITS() = 4``
+
+Then in the struct memory layout, this member will occupy ``4`` bits starting
+from bits ``100 + 2 = 102``.
+
+Alternatively, the bitfield struct member can be the following to access the
+same bits as the above:
+
+ * btf member bit offset 102,
+ * btf member pointing to an int type,
+ * the int type has ``BTF_INT_OFFSET() = 0`` and ``BTF_INT_BITS() = 4``
+
+The original intention of ``BTF_INT_OFFSET()`` is to provide flexibility of
+bitfield encoding. Currently, both llvm and pahole generate
+``BTF_INT_OFFSET() = 0`` for all int types.
+
+2.2.2 BTF_KIND_PTR
+~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_PTR
+  * ``info.vlen``: 0
+  * ``type``: the pointee type of the pointer
+
+No additional type data follow ``btf_type``.
+
+2.2.3 BTF_KIND_ARRAY
+~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_ARRAY
+  * ``info.vlen``: 0
+  * ``size/type``: 0, not used
+
+``btf_type`` is followed by one ``struct btf_array``::
+
+    struct btf_array {
+        __u32   type;
+        __u32   index_type;
+        __u32   nelems;
+    };
+
+The ``struct btf_array`` encoding:
+  * ``type``: the element type
+  * ``index_type``: the index type
+  * ``nelems``: the number of elements for this array (``0`` is also allowed).
+
+The ``index_type`` can be any regular int type (``u8``, ``u16``, ``u32``,
+``u64``, ``unsigned __int128``). The original design of including
+``index_type`` follows DWARF, which has an ``index_type`` for its array type.
+Currently in BTF, beyond type verification, the ``index_type`` is not used.
+
+The ``struct btf_array`` allows chaining through element type to represent
+multidimensional arrays. For example, for ``int a[5][6]``, the following type
+information illustrates the chaining:
+
+  * [1]: int
+  * [2]: array, ``btf_array.type = [1]``, ``btf_array.nelems = 6``
+  * [3]: array, ``btf_array.type = [2]``, ``btf_array.nelems = 5``
+
+Currently, both pahole and llvm collapse multidimensional array into
+one-dimensional array, e.g., for ``a[5][6]``, the ``btf_array.nelems`` is
+equal to ``30``. This is because the original use case is map pretty print
+where the whole array is dumped out so one-dimensional array is enough. As
+more BTF usage is explored, pahole and llvm can be changed to generate proper
+chained representation for multidimensional arrays.
+
+2.2.4 BTF_KIND_STRUCT
+~~~~~~~~~~~~~~~~~~~~~
+2.2.5 BTF_KIND_UNION
+~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0 or offset to a valid C identifier
+  * ``info.kind_flag``: 0 or 1
+  * ``info.kind``: BTF_KIND_STRUCT or BTF_KIND_UNION
+  * ``info.vlen``: the number of struct/union members
+  * ``info.size``: the size of the struct/union in bytes
+
+``btf_type`` is followed by ``info.vlen`` number of ``struct btf_member``.::
+
+    struct btf_member {
+        __u32   name_off;
+        __u32   type;
+        __u32   offset;
+    };
+
+``struct btf_member`` encoding:
+  * ``name_off``: offset to a valid C identifier
+  * ``type``: the member type
+  * ``offset``: <see below>
+
+If the type info ``kind_flag`` is not set, the offset contains only bit offset
+of the member. Note that the base type of the bitfield can only be int or enum
+type. If the bitfield size is 32, the base type can be either int or enum
+type. If the bitfield size is not 32, the base type must be int, and int type
+``BTF_INT_BITS()`` encodes the bitfield size.
+
+If the ``kind_flag`` is set, the ``btf_member.offset`` contains both member
+bitfield size and bit offset. The bitfield size and bit offset are calculated
+as below.::
+
+  #define BTF_MEMBER_BITFIELD_SIZE(val)   ((val) >> 24)
+  #define BTF_MEMBER_BIT_OFFSET(val)      ((val) & 0xffffff)
+
+In this case, if the base type is an int type, it must be a regular int type:
+
+  * ``BTF_INT_OFFSET()`` must be 0.
+  * ``BTF_INT_BITS()`` must be equal to ``{1,2,4,8,16} * 8``.
+
+The following kernel patch introduced ``kind_flag`` and explained why both
+modes exist:
+
+  https://github.com/torvalds/linux/commit/9d5f9f701b1891466fb3dbb1806ad97716f95cc3#diff-fa650a64fdd3968396883d2fe8215ff3
+
+2.2.6 BTF_KIND_ENUM
+~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0 or offset to a valid C identifier
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_ENUM
+  * ``info.vlen``: number of enum values
+  * ``size``: 4
+
+``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum``.::
+
+    struct btf_enum {
+        __u32   name_off;
+        __s32   val;
+    };
+
+The ``btf_enum`` encoding:
+  * ``name_off``: offset to a valid C identifier
+  * ``val``: any value
+
+2.2.7 BTF_KIND_FWD
+~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: offset to a valid C identifier
+  * ``info.kind_flag``: 0 for struct, 1 for union
+  * ``info.kind``: BTF_KIND_FWD
+  * ``info.vlen``: 0
+  * ``type``: 0
+
+No additional type data follow ``btf_type``.
+
+2.2.8 BTF_KIND_TYPEDEF
+~~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: offset to a valid C identifier
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_TYPEDEF
+  * ``info.vlen``: 0
+  * ``type``: the type which can be referred by name at ``name_off``
+
+No additional type data follow ``btf_type``.
+
+2.2.9 BTF_KIND_VOLATILE
+~~~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_VOLATILE
+  * ``info.vlen``: 0
+  * ``type``: the type with ``volatile`` qualifier
+
+No additional type data follow ``btf_type``.
+
+2.2.10 BTF_KIND_CONST
+~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_CONST
+  * ``info.vlen``: 0
+  * ``type``: the type with ``const`` qualifier
+
+No additional type data follow ``btf_type``.
+
+2.2.11 BTF_KIND_RESTRICT
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_RESTRICT
+  * ``info.vlen``: 0
+  * ``type``: the type with ``restrict`` qualifier
+
+No additional type data follow ``btf_type``.
+
+2.2.12 BTF_KIND_FUNC
+~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: offset to a valid C identifier
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_FUNC
+  * ``info.vlen``: 0
+  * ``type``: a BTF_KIND_FUNC_PROTO type
+
+No additional type data follow ``btf_type``.
+
+A BTF_KIND_FUNC defines not a type, but a subprogram (function) whose
+signature is defined by ``type``. The subprogram is thus an instance of that
+type. The BTF_KIND_FUNC may in turn be referenced by a func_info in the
+:ref:`BTF_Ext_Section` (ELF) or in the arguments to :ref:`BPF_Prog_Load`
+(ABI).
+
+2.2.13 BTF_KIND_FUNC_PROTO
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+  * ``name_off``: 0
+  * ``info.kind_flag``: 0
+  * ``info.kind``: BTF_KIND_FUNC_PROTO
+  * ``info.vlen``: # of parameters
+  * ``type``: the return type
+
+``btf_type`` is followed by ``info.vlen`` number of ``struct btf_param``.::
+
+    struct btf_param {
+        __u32   name_off;
+        __u32   type;
+    };
+
+If a BTF_KIND_FUNC_PROTO type is referred by a BTF_KIND_FUNC type, then
+``btf_param.name_off`` must point to a valid C identifier except for the
+possible last argument representing the variable argument. The btf_param.type
+refers to parameter type.
+
+If the function has variable arguments, the last parameter is encoded with
+``name_off = 0`` and ``type = 0``.
+
+3. BTF Kernel API
+*****************
+
+The following bpf syscall command involves BTF:
+   * BPF_BTF_LOAD: load a blob of BTF data into kernel
+   * BPF_MAP_CREATE: map creation with btf key and value type info.
+   * BPF_PROG_LOAD: prog load with btf function and line info.
+   * BPF_BTF_GET_FD_BY_ID: get a btf fd
+   * BPF_OBJ_GET_INFO_BY_FD: btf, func_info, line_info
+     and other btf related info are returned.
+
+The workflow typically looks like:
+::
+
+  Application:
+      BPF_BTF_LOAD
+          |
+          v
+      BPF_MAP_CREATE and BPF_PROG_LOAD
+          |
+          V
+      ......
+
+  Introspection tool:
+      ......
+      BPF_{PROG,MAP}_GET_NEXT_ID (get prog/map id's)
+          |
+          V
+      BPF_{PROG,MAP}_GET_FD_BY_ID (get a prog/map fd)
+          |
+          V
+      BPF_OBJ_GET_INFO_BY_FD (get bpf_prog_info/bpf_map_info with btf_id)
+          |                                     |
+          V                                     |
+      BPF_BTF_GET_FD_BY_ID (get btf_fd)         |
+          |                                     |
+          V                                     |
+      BPF_OBJ_GET_INFO_BY_FD (get btf)          |
+          |                                     |
+          V                                     V
+      pretty print types, dump func signatures and line info, etc.
+
+
+3.1 BPF_BTF_LOAD
+================
+
+Load a blob of BTF data into kernel. A blob of data, described in
+:ref:`BTF_Type_String`, can be directly loaded into the kernel. A ``btf_fd``
+is returned to a userspace.
+
+3.2 BPF_MAP_CREATE
+==================
+
+A map can be created with ``btf_fd`` and specified key/value type id.::
+
+    __u32   btf_fd;         /* fd pointing to a BTF type data */
+    __u32   btf_key_type_id;        /* BTF type_id of the key */
+    __u32   btf_value_type_id;      /* BTF type_id of the value */
+
+In libbpf, the map can be defined with extra annotation like below:
+::
+
+    struct bpf_map_def SEC("maps") btf_map = {
+        .type = BPF_MAP_TYPE_ARRAY,
+        .key_size = sizeof(int),
+        .value_size = sizeof(str