Merge branch 'bpf_iter'

Yonghong Song says:

====================
Motivation:
  The current way to dump kernel data structures mostly:
    1. /proc system
    2. various specific tools like "ss" which requires kernel support.
    3. drgn
  The dropback for the first two is that whenever you want to dump more, you
  need change the kernel. For example, Martin wants to dump socket local
  storage with "ss". Kernel change is needed for it to work ([1]).
  This is also the direct motivation for this work.

  drgn ([2]) solves this proble nicely and no kernel change is not needed.
  But since drgn is not able to verify the validity of a particular pointer value,
  it might present the wrong results in rare cases.

  In this patch set, we introduce bpf iterator. Initial kernel changes are
  still needed for interested kernel data, but a later data structure change
  will not require kernel changes any more. bpf program itself can adapt
  to new data structure changes. This will give certain flexibility with
  guaranteed correctness.

  In this patch set, kernel seq_ops is used to facilitate iterating through
  kernel data, similar to current /proc and many other lossless kernel
  dumping facilities. In the future, different iterators can be
  implemented to trade off losslessness for other criteria e.g. no
  repeated object visits, etc.

User Interface:
  1. Similar to prog/map/link, the iterator can be pinned into a
     path within a bpffs mount point.
  2. The bpftool command can pin an iterator to a file
         bpftool iter pin <bpf_prog.o> <path>
  3. Use `cat <path>` to dump the contents.
     Use `rm -f <path>` to remove the pinned iterator.
  4. The anonymous iterator can be created as well.

  Please see patch #19 andd #20 for bpf programs and bpf iterator
  output examples.

  Note that certain iterators are namespace aware. For example,
  task and task_file targets only iterate through current pid namespace.
  ipv6_route and netlink will iterate through current net namespace.

  Please see individual patches for implementation details.

Performance:
  The bpf iterator provides in-kernel aggregation abilities
  for kernel data. This can greatly improve performance
  compared to e.g., iterating all process directories under /proc.
  For example, I did an experiment on my VM with an application forking
  different number of tasks and each forked process opening various number
  of files. The following is the result with the latency with unit of microseconds:

    # of forked tasks   # of open files    # of bpf_prog calls  # latency (us)
    100                 100                11503                7586
    1000                1000               1013203              709513
    10000               100                1130203              764519

  The number of bpf_prog calls may be more than forked tasks multipled by
  open files since there are other tasks running on the system.
  The bpf program is a do-nothing program. One millions of bpf calls takes
  less than one second.

  Although the initial motivation is from Martin's sk_local_storage,
  this patch didn't implement tcp6 sockets and sk_local_storage.
  The /proc/net/tcp6 involves three types of sockets, timewait,
  request and tcp6 sockets. Some kind of type casting or other
  mechanism is needed to handle all these socket types in one
  bpf program. This will be addressed in future work.

  Currently, we do not support kernel data generated under module.
  This requires some BTF work.

  More work for more iterators, e.g., tcp, udp, bpf_map elements, etc.

Changelog:
  v3 -> v4:
    - in bpf_seq_read(), if start() failed with an error, return that
      error to user space (Andrii)
    - in bpf_seq_printf(), if reading kernel memory failed for
      %s and %p{i,I}{4,6}, set buffer to empty string or address 0.
      Documented this behavior in uapi header (Andrii)
    - fix a few error handling issues for bpftool (Andrii)
    - A few other minor fixes and cosmetic changes.
  v2 -> v3:
    - add bpf_iter_unreg_target() to unregister a target, used in the
      error path of the __init functions.
    - handle err != 0 before handling overflow (Andrii)
    - reference count "task" for task_file target (Andrii)
    - remove some redundancy for bpf_map/task/task_file targets
    - add bpf_iter_unreg_target() in ip6_route_cleanup()
    - Handling "%%" format in bpf_seq_printf() (Andrii)
    - implement auto-attach for bpf_iter in libbpf (Andrii)
    - add macros offsetof and container_of in bpf_helpers.h (Andrii)
    - add tests for auto-attach and program-return-1 cases
    - some other minor fixes
  v1 -> v2:
    - removed target_feature, using callback functions instead
    - checking target to ensure program specified btf_id supported (Martin)
    - link_create change with new changes from Andrii
    - better handling of btf_iter vs. seq_file private data (Martin, Andrii)
    - implemented bpf_seq_read() (Andrii, Alexei)
    - percpu buffer for bpf_seq_printf() (Andrii)
    - better syntax for BPF_SEQ_PRINTF macro (Andrii)
    - bpftool fixes (Quentin)
    - a lot of other fixes
  RFC v2 -> v1:
    - rename bpfdump to bpf_iter
    - use bpffs instead of a new file system
    - use bpf_link to streamline and simplify iterator creation.

References:
  [1]: https://lore.kernel.org/bpf/20200225230427.1976129-1-kafai@fb.com
  [2]: https://github.com/osandov/drgn
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

25 files changed, 1055 insertions, 2 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-iter.rst b/tools/bpf/bpftool/Documentation/bpftool-iter.rst
new file mode 100644
index 000000000000..13b173d93890
--- /dev/null
+++ b/tools/bpf/bpftool/Documentation/bpftool-iter.rst
@@ -0,0 +1,83 @@
+============
+bpftool-iter
+============
+-------------------------------------------------------------------------------
+tool to create BPF iterators
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **iter** *COMMAND*
+
+	*COMMANDS* := { **pin** | **help** }
+
+ITER COMMANDS
+===================
+
+|	**bpftool** **iter pin** *OBJ* *PATH*
+|	**bpftool** **iter help**
+|
+|	*OBJ* := /a/file/of/bpf_iter_target.o
+
+
+DESCRIPTION
+===========
+	**bpftool iter pin** *OBJ* *PATH*
+		  A bpf iterator combines a kernel iterating of
+		  particular kernel data (e.g., tasks, bpf_maps, etc.)
+		  and a bpf program called for each kernel data object
+		  (e.g., one task, one bpf_map, etc.). User space can
+		  *read* kernel iterator output through *read()* syscall.
+
+		  The *pin* command creates a bpf iterator from *OBJ*,
+		  and pin it to *PATH*. The *PATH* should be located
+		  in *bpffs* mount. It must not contain a dot
+		  character ('.'), which is reserved for future extensions
+		  of *bpffs*.
+
+		  User can then *cat PATH* to see the bpf iterator output.
+
+	**bpftool iter help**
+		  Print short help message.
+
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-V, --version
+		  Print version number (similar to **bpftool version**).
+
+	-d, --debug
+		  Print all logs available, even debug-level information. This
+		  includes logs from libbpf as well as from the verifier, when
+		  attempting to load programs.
+
+EXAMPLES
+========
+**# bpftool iter pin bpf_iter_netlink.o /sys/fs/bpf/my_netlink**
+
+::
+
+   Create a file-based bpf iterator from bpf_iter_netlink.o and pin it
+   to /sys/fs/bpf/my_netlink
+
+
+SEE ALSO
+========
+	**bpf**\ (2),
+	**bpf-helpers**\ (7),
+	**bpftool**\ (8),
+	**bpftool-prog**\ (8),
+	**bpftool-map**\ (8),
+	**bpftool-link**\ (8),
+	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
+	**bpftool-net**\ (8),
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)
+	**bpftool-gen**\ (8)
+	**bpftool-struct_ops**\ (8)
diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
index fc989ead7313..9f0f20e73b87 100644
--- a/tools/bpf/bpftool/bash-completion/bpftool
+++ b/tools/bpf/bpftool/bash-completion/bpftool
@@ -610,6 +610,19 @@ _bpftool()
                     ;;
             esac
             ;;
+        iter)
+            case $command in
+                pin)
+                    _filedir
+                    return 0
+                    ;;
+                *)
+                    [[ $prev == $object ]] && \
+                        COMPREPLY=( $( compgen -W 'pin help' \
+                            -- "$cur" ) )
+                    ;;
+            esac
+            ;;
         map)
             local MAP_TYPE='id pinned name'
             case $command in
diff --git a/tools/bpf/bpftool/iter.c b/tools/bpf/bpftool/iter.c
new file mode 100644
index 000000000000..eb5987a0c3b6
--- /dev/null
+++ b/tools/bpf/bpftool/iter.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+// Copyright (C) 2020 Facebook
+
+#define _GNU_SOURCE
+#include <linux/err.h>
+#include <bpf/libbpf.h>
+
+#include "main.h"
+
+static int do_pin(int argc, char **argv)
+{
+	const char *objfile, *path;
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	struct bpf_link *link;
+	int err;
+
+	if (!REQ_ARGS(2))
+		usage();
+
+	objfile = GET_ARG();
+	path = GET_ARG();
+
+	obj = bpf_object__open(objfile);
+	if (IS_ERR(obj)) {
+		p_err("can't open objfile %s", objfile);
+		return -1;
+	}
+
+	err = bpf_object__load(obj);
+	if (err) {
+		p_err("can't load objfile %s", objfile);
+		goto close_obj;
+	}
+
+	prog = bpf_program__next(NULL, obj);
+	if (!prog) {
+		p_err("can't find bpf program in objfile %s", objfile);
+		goto close_obj;
+	}
+
+	link = bpf_program__attach_iter(prog, NULL);
+	if (IS_ERR(link)) {
+		err = PTR_ERR(link);
+		p_err("attach_iter failed for program %s",
+		      bpf_program__name(prog));
+		goto close_obj;
+	}
+
+	err = mount_bpffs_for_pin(path);
+	if (err)
+		goto close_link;
+
+	err = bpf_link__pin(link, path);
+	if (err) {
+		p_err("pin_iter failed for program %s to path %s",
+		      bpf_program__name(prog), path);
+		goto close_link;
+	}
+
+close_link:
+	bpf_link__destroy(link);
+close_obj:
+	bpf_object__close(obj);
+	return err;
+}
+
+static int do_help(int argc, char **argv)
+{
+	fprintf(stderr,
+		"Usage: %s %s pin OBJ PATH\n"
+		"       %s %s help\n"
+		"\n",
+		bin_name, argv[-2], bin_name, argv[-2]);
+
+	return 0;
+}
+
+static const struct cmd cmds[] = {
+	{ "help",	do_help },
+	{ "pin",	do_pin },
+	{ 0 }
+};
+
+int do_iter(int argc, char **argv)
+{
+	return cmd_select(cmds, argc, argv, do_help);
+}
diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index adc7dc431ed8..b6a0b35c78ae 100644
--- a/tools/bpf/bpftool/link.c
+++ b/tools/bpf/bpftool/link.c
@@ -16,6 +16,7 @@ static const char * const link_type_name[] = {
 	[BPF_LINK_TYPE_RAW_TRACEPOINT]		= "raw_tracepoint",
 	[BPF_LINK_TYPE_TRACING]			= "tracing",
 	[BPF_LINK_TYPE_CGROUP]			= "cgroup",
+	[BPF_LINK_TYPE_ITER]			= "iter",
 };
 
 static int link_parse_fd(int *argc, char ***argv)
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 1413a154806e..46bd716a9d86 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -59,7 +59,7 @@ static int do_help(int argc, char **argv)
 		"       %s batch file FILE\n"
 		"       %s version\n"
 		"\n"
-		"       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops }\n"
+		"       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops | iter }\n"
 		"       " HELP_SPEC_OPTIONS "\n"
 		"",
 		bin_name, bin_name, bin_name);
@@ -224,6 +224,7 @@ static const struct cmd cmds[] = {
 	{ "btf",	do_btf },
 	{ "gen",	do_gen },
 	{ "struct_ops",	do_struct_ops },
+	{ "iter",	do_iter },
 	{ "version",	do_version },
 	{ 0 }
 };
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 9b1fb81a8331..a41cefabccaf 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -199,6 +199,7 @@ int do_feature(int argc, char **argv);
 int do_btf(int argc, char **argv);
 int do_gen(int argc, char **argv);
 int do_struct_ops(int argc, char **argv);
+int do_iter(int argc, char **argv);
 
 int parse_u32_arg(int *argc, char ***argv, __u32 *val, const char *what);
 int prog_parse_fd(int *argc, char ***argv);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 6e5e7caa3739..9d1932e23cec 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -116,6 +116,7 @@ enum bpf_cmd {
 	BPF_LINK_GET_FD_BY_ID,
 	BPF_LINK_GET_NEXT_ID,
 	BPF_ENABLE_STATS,
+	BPF_ITER_CREATE,
 };
 
 enum bpf_map_type {
@@ -218,6 +219,7 @@ enum bpf_attach_type {
 	BPF_TRACE_FEXIT,
 	BPF_MODIFY_RETURN,
 	BPF_LSM_MAC,
+	BPF_TRACE_ITER,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -228,6 +230,7 @@ enum bpf_link_type {
 	BPF_LINK_TYPE_RAW_TRACEPOINT = 1,
 	BPF_LINK_TYPE_TRACING = 2,
 	BPF_LINK_TYPE_CGROUP = 3,
+	BPF_LINK_TYPE_ITER = 4,
 
 	MAX_BPF_LINK_TYPE,
 };
@@ -612,6 +615,11 @@ union bpf_attr {
 		__u32		type;
 	} enable_stats;
 
+	struct { /* struct used by BPF_ITER_CREATE command */
+		__u32		link_fd;
+		__u32		flags;
+	} iter_create;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
@@ -3069,6 +3077,41 @@ union bpf_attr {
  * 		See: clock_gettime(CLOCK_BOOTTIME)
  * 	Return
  * 		Current *ktime*.
+ *
+ * int bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const void *data, u32 data_len)
+ * 	Description
+ * 		seq_printf uses seq_file seq_printf() to print out the format string.
+ * 		The *m* represents the seq_file. The *fmt* and *fmt_size* are for
+ * 		the format string itself. The *data* and *data_len* are format string
+ * 		arguments. The *data* are a u64 array and corresponding format string
+ * 		values are stored in the array. For strings and pointers where pointees
+ * 		are accessed, only the pointer values are stored in the *data* array.
+ * 		The *data_len* is the *data* size in term of bytes.
+ *
+ *		Formats **%s**, **%p{i,I}{4,6}** requires to read kernel memory.
+ *		Reading kernel memory may fail due to either invalid address or
+ *		valid address but requiring a major memory fault. If reading kernel memory
+ *		fails, the string for **%s** will be an empty string, and the ip
+ *		address for **%p{i,I}{4,6}** will be 0. Not returning error to
+ *		bpf program is consistent with what bpf_trace_printk() does for now.
+ * 	Return
+ * 		0 on success, or a negative errno in case of failure.
+ *
+ *		* **-EBUSY**		Percpu memory copy buffer is busy, can try again
+ *					by returning 1 from bpf program.
+ *		* **-EINVAL**		Invalid arguments, or invalid/unsupported formats.
+ *		* **-E2BIG**		Too many format specifiers.
+ *		* **-EOVERFLOW**	Overflow happens, the same object will be tried again.
+ *
+ * int bpf_seq_write(struct seq_file *m, const void *data, u32 len)
+ * 	Description
+ * 		seq_write uses seq_file seq_write() to write the data.
+ * 		The *m* represents the seq_file. The *data* and *len* represent the
+ *		data to write in bytes.
+ * 	Return
+ * 		0 on success, or a negative errno in case of failure.
+ *
+ *		* **-EOVERFLOW**	Overflow happens, the same object will be tried again.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3196,7 +3239,9 @@ union bpf_attr {
 	FN(get_netns_cookie),		\
 	FN(get_current_ancestor_cgroup_id),	\
 	FN(sk_assign),			\
-	FN(ktime_get_boot_ns),
+	FN(ktime_get_boot_ns),		\
+	FN(seq_printf),			\
+	FN(seq_write),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 43322f0d6c7f..a7329b671c41 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -619,6 +619,16 @@ int bpf_link_update(int link_fd, int new_prog_fd,
 	return sys_bpf(BPF_LINK_UPDATE, &attr, sizeof(attr));
 }
 
+int bpf_iter_create(int link_fd)
+{
+	union bpf_attr attr;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.iter_create.link_fd = link_fd;
+
+	return sys_bpf(BPF_ITER_CREATE, &attr, sizeof(attr));
+}
+
 int bpf_prog_query(int target_fd, enum bpf_attach_type type, __u32 query_flags,
 		   __u32 *attach_flags, __u32 *prog_ids, __u32 *prog_cnt)
 {
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 1901b2777854..1b6015b21ba8 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -187,6 +187,8 @@ struct bpf_link_update_opts {
 LIBBPF_API int bpf_link_update(int link_fd, int new_prog_fd,
 			       const struct bpf_link_update_opts *opts);
 
+LIBBPF_API int bpf_iter_create(int link_fd);
+
 struct bpf_prog_test_run_attr {
 	int prog_fd;
 	int repeat;
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index da00b87aa199..f67dce2af802 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -37,6 +37,20 @@
 #endif
 
 /*
+ * Helper macro to manipulate data structures
+ */
+#ifndef offsetof
+#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)
+#endif
+#ifndef container_of
+#define container_of(ptr, type, member)				\
+	({							\
+		void *__mptr = (void *)(ptr);			\
+		((type *)(__mptr - offsetof(type, member)));	\
+	})
+#endif
+
+/*
  * Helper structure used by eBPF C program
  * to describe BPF map attributes to libbpf loader
  */
diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
index f3f3c3fb98cb..cf97d07692b4 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -413,4 +413,20 @@ typeof(name(0)) name(struct pt_regs *ctx)				    \
 }									    \
 static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
 
+/*
+ * BPF_SEQ_PRINTF to wrap bpf_seq_printf to-be-printed values
+ * in a structure.
+ */
+#define BPF_SEQ_PRINTF(seq, fmt, args...)				    \
+	({								    \
+		_Pragma("GCC diagnostic push")				    \
+		_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")	    \
+		static const char ___fmt[] = fmt;			    \
+		unsigned long long ___param[] = { args };		    \
+		_Pragma("GCC diagnostic pop")				    \
+		int ___ret = bpf_seq_printf(seq, ___fmt, sizeof(___fmt),    \
+					    ___param, sizeof(___param));    \
+		___ret;							    \
+	})
+
 #endif
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 977add1b73e2..6c2f46908f4d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6586,6 +6586,8 @@ static struct bpf_link *attach_trace(const struct bpf_sec_def *sec,
 				     struct bpf_program *prog);
 static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
 				   struct bpf_program *prog);
+static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
+				    struct bpf_program *prog);
 
 static const struct bpf_sec_def section_defs[] = {
 	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
@@ -6629,6 +6631,10 @@ static const struct bpf_sec_def section_defs[] = {
 		.is_attach_btf = true,
 		.expected_attach_type = BPF_LSM_MAC,
 		.attach_fn = attach_lsm),
+	SEC_DEF("iter/", TRACING,
+		.expected_attach_type = BPF_TRACE_ITER,
+		.is_attach_btf = true,
+		.attach_fn = attach_iter),
 	BPF_PROG_SEC("xdp",			BPF_PROG_TYPE_XDP),
 	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
 	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
@@ -6891,6 +6897,7 @@ invalid_prog:
 
 #define BTF_TRACE_PREFIX "btf_trace_"
 #define BTF_LSM_PREFIX "bpf_lsm_"
+#define BTF_ITER_PREFIX "__bpf_iter__"
 #define BTF_MAX_NAME_SIZE 128
 
 static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
@@ -6921,6 +6928,9 @@ static inline int __find_vmlinux_btf_id(struct btf *btf, const char *name,
 	else if (attach_type == BPF_LSM_MAC)
 		err = find_btf_by_prefix_kind(btf, BTF_LSM_PREFIX, name,
 					      BTF_KIND_FUNC);
+	else if (attach_type == BPF_TRACE_ITER)
+		err = find_btf_by_prefix_kind(btf, BTF_ITER_PREFIX, name,
+					      BTF_KIND_FUNC);
 	else
 		err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
 
@@ -7848,6 +7858,12 @@ static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
 	return bpf_program__attach_lsm(prog);
 }
 
+static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
+				    struct bpf_program *prog)
+{
+	return bpf_program__attach_iter(prog, NULL);
+}
+
 struct bpf_link *
 bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
 {
@@ -7882,6 +7898,42 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
 	return link;
 }
 
+struct bpf_link *
+bpf_program__attach_iter(struct bpf_program *prog,
+			 const struct bpf_iter_attach_opts *opts)
+{
+	char errmsg[STRERR_BUFSIZE];
+	struct bpf_link *link;
+	int prog_fd, link_fd;
+
+	if (!OPTS_VALID(opts, bpf_iter_attach_opts))
+		return ERR_PTR(-EINVAL);
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("program '%s': can't attach before loaded\n",
+			bpf_program__title(prog, false));
+		return ERR_PTR(-EINVAL);
+	}
+
+	link = calloc(1, sizeof(*link));
+	if (!link)
+		return ERR_PTR(-ENOMEM);
+	link->detach = &bpf_link__detach_fd;
+
+	link_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_ITER, NULL);
+	if (link_fd < 0) {
+		link_fd = -errno;
+		free(link);
+		pr_warn("program '%s': failed to attach to iterator: %s\n",
+			bpf_program__title(prog, false),
+			libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
+		return ERR_PTR(link_fd);
+	}
+	link->fd = link_fd;
+	return link;
+}
+
 struct bpf_link *bpf_program__attach(struct bpf_program *prog)
 {
 	const struct bpf_sec_def *sec_def;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index f1dacecb1619..8ea69558f0a8 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -258,6 +258,15 @@ struct bpf_map;
 
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(struct bpf_map *map);
 
+struct bpf_iter_attach_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+};
+#define bpf_iter_attach_opts__last_field sz
+
+LIBBPF_API struct bpf_link *
+bpf_program__attach_iter(struct bpf_program *prog,
+			 const struct bpf_iter_attach_opts *opts);
+
 struct bpf_insn;
 
 /*
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index e03bd4db827e..0133d469d30b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -258,6 +258,8 @@ LIBBPF_0.0.8 {
 LIBBPF_0.0.9 {
 	global:
 		bpf_enable_stats;
+		bpf_iter_create;
 		bpf_link_get_fd_by_id;
 		bpf_link_get_next_id;
+		bpf_program__attach_iter;
 } LIBBPF_0.0.8;
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
new file mode 100644
index 000000000000..87c29dde1cf9
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -0,0 +1,409 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <test_progs.h>
+#include "bpf_iter_ipv6_route.skel.h"
+#include "bpf_iter_netlink.skel.h"
+#include "bpf_iter_bpf_map.skel.h"
+#include "bpf_iter_task.skel.h"
+#include "bpf_iter_task_file.skel.h"
+#include "bpf_iter_test_kern1.skel.h"
+#include "bpf_iter_test_kern2.skel.h"
+#include "bpf_iter_test_kern3.skel.h"
+#include "bpf_iter_test_kern4.skel.h"
+
+static int duration;
+
+static void test_btf_id_or_null(void)
+{
+	struct bpf_iter_test_kern3 *skel;
+
+	skel = bpf_iter_test_kern3__open_and_load();
+	if (CHECK(skel, "bpf_iter_test_kern3__open_and_load",
+		  "skeleton open_and_load unexpectedly succeeded\n")) {
+		bpf_iter_test_kern3__destroy(skel);
+		return;
+	}
+}
+
+static void do_dummy_read(struct bpf_program *prog)
+{
+	struct bpf_link *link;
+	char buf[16] = {};
+	int iter_fd, len;
+
+	link = bpf_program__attach_iter(prog, NULL);
+	if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
+		return;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto free_link;
+
+	/* not check contents, but ensure read() ends without error */
+	while ((len = read(iter_fd, buf, sizeof(buf))) > 0)
+		;
+	CHECK(len < 0, "read", "read failed: %s\n", strerror(errno));
+
+	close(iter_fd);
+
+free_link:
+	bpf_link__destroy(link);
+}
+
+static void test_ipv6_route(void)
+{
+	struct bpf_iter_ipv6_route *skel;
+
+	skel = bpf_iter_ipv6_route__open_and_load();
+	if (CHECK(!skel, "bpf_iter_ipv6_route__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_ipv6_route);
+
+	bpf_iter_ipv6_route__destroy(skel);
+}
+
+static void test_netlink(void)
+{
+	struct bpf_iter_netlink *skel;
+
+	skel = bpf_iter_netlink__open_and_load();
+	if (CHECK(!skel, "bpf_iter_netlink__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_netlink);
+
+	bpf_iter_netlink__destroy(skel);
+}
+
+static void test_bpf_map(void)
+{
+	struct bpf_iter_bpf_map *skel;
+
+	skel = bpf_iter_bpf_map__open_and_load();
+	if (CHECK(!skel, "bpf_iter_bpf_map__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_bpf_map);
+
+	bpf_iter_bpf_map__destroy(skel);
+}
+
+static void test_task(void)
+{
+	struct bpf_iter_task *skel;
+
+	skel = bpf_iter_task__open_and_load();
+	if (CHECK(!skel, "bpf_iter_task__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_task);
+
+	bpf_iter_task__destroy(skel);
+}
+
+static void test_task_file(void)
+{
+	struct bpf_iter_task_file *skel;
+
+	skel = bpf_iter_task_file__open_and_load();
+	if (CHECK(!skel, "bpf_iter_task_file__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	do_dummy_read(skel->progs.dump_task_file);
+
+	bpf_iter_task_file__destroy(skel);
+}
+
+/* The expected string is less than 16 bytes */
+static int do_read_with_fd(int iter_fd, const char *expected,
+			   bool read_one_char)
+{
+	int err = -1, len, read_buf_len, start;
+	char buf[16] = {};
+
+	read_buf_len = read_one_char ? 1 : 16;
+	start = 0;
+	while ((len = read(iter_fd, buf + start, read_buf_len)) > 0) {
+		start += len;
+		if (CHECK(start >= 16, "read", "read len %d\n", len))
+			return -1;
+		read_buf_len = read_one_char ? 1 : 16 - start;
+	}
+	if (CHECK(len < 0, "read", "read failed: %s\n", strerror(errno)))
+		return -1;
+
+	err = strcmp(buf, expected);
+	if (CHECK(err, "read", "incorrect read result: buf %s, expected %s\n",
+		  buf, expected))
+		return -1;
+
+	return 0;
+}
+
+static void test_anon_iter(bool read_one_char)
+{
+	struct bpf_iter_test_kern1 *skel;
+	struct bpf_link *link;
+	int iter_fd, err;
+
+	skel = bpf_iter_test_kern1__open_and_load();
+	if (CHECK(!skel, "bpf_iter_test_kern1__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	err = bpf_iter_test_kern1__attach(skel);
+	if (CHECK(err, "bpf_iter_test_kern1__attach",
+		  "skeleton attach failed\n")) {
+		goto out;
+	}
+
+	link = skel->links.dump_task;
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto out;
+
+	do_read_with_fd(iter_fd, "abcd", read_one_char);
+	close(iter_fd);
+
+out:
+	bpf_iter_test_kern1__destroy(skel);
+}
+
+static int do_read(const char *path, const char *expected)
+{
+	int err, iter_fd;
+
+	iter_fd = open(path, O_RDONLY);
+	if (CHECK(iter_fd < 0, "open", "open %s failed: %s\n",
+		  path, strerror(errno)))
+		return -1;
+
+	err = do_read_with_fd(iter_fd, expected, false);
+	close(iter_fd);
+	return err;
+}
+
+static void test_file_iter(void)
+{
+	const char *path = "/sys/fs/bpf/bpf_iter_test1";
+	struct bpf_iter_test_kern1 *skel1;
+	struct bpf_iter_test_kern2 *skel2;
+	struct bpf_link *link;
+	int err;
+
+	skel1 = bpf_iter_test_kern1__open_and_load();
+	if (CHECK(!skel1, "bpf_iter_test_kern1__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		return;
+
+	link = bpf_program__attach_iter(skel1->progs.dump_task, NULL);
+	if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
+		goto out;
+
+	/* unlink this path if it exists. */
+	unlink(path);
+
+	err = bpf_link__pin(link, path);
+	if (CHECK(err, "pin_iter", "pin_iter to %s failed: %d\n", path, err))
+		goto free_link;
+
+	err = do_read(path, "abcd");
+	if (err)
+		goto unlink_path;
+
+	/* file based iterator seems working fine. Let us a link update
+	 * of the underlying link and `cat` the iterator again, its content
+	 * should change.
+	 */
+	skel2 = bpf_iter_test_kern2__open_and_load();
+	if (CHECK(!skel2, "bpf_iter_test_kern2__open_and_load",
+		  "skeleton open_and_load failed\n"))
+		goto unlink_path;
+
+	err = bpf_link__update_program(link, skel2->progs.dump_task);
+	if (CHECK(err, "update_prog", "update_prog failed\n"))
+		goto destroy_skel2;
+
+	do_read(path, "ABCD");
+
+destroy_skel2:
+	bpf_iter_test_kern2__destroy(skel2);
+unlink_path:
+	unlink(path);
+free_link:
+	bpf_link__destroy(link);
+out:
+	bpf_iter_test_kern1__destroy(skel1);
+}
+
+static void test_overflow(bool test_e2big_overflow, bool ret1)
+{
+	__u32 map_info_len, total_read_len, expected_read_len;
+	int err, iter_fd, map1_fd, map2_fd, len;
+	struct bpf_map_info map_info = {};
+	struct bpf_iter_test_kern4 *skel;
+	struct bpf_link *link;
+	__u32 page_size;
+	char *buf;
+
+	skel = bpf_iter_test_kern4__open();
+	if (CHECK(!skel, "bpf_iter_test_kern4__open",
+		  "skeleton open failed\n"))
+		return;
+
+	/* create two maps: bpf program will only do bpf_seq_write
+	 * for these two maps. The goal is one map output almost
+	 * fills seq_file buffer and then the other will trigger
+	 * overflow and needs restart.
+	 */
+	map1_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 8, 1, 0);
+	if (CHECK(map1_fd < 0, "bpf_create_map",
+		  "map_creation failed: %s\n", strerror(errno)))
+		goto out;
+	map2_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 8, 1, 0);
+	if (CHECK(map2_fd < 0, "bpf_create_map",
+		  "map_creation failed: %s\n", strerror(errno)))
+		goto free_map1;
+
+	/* bpf_seq_printf kernel buffer is one page, so one map
+	 * bpf_seq_write will mostly fill it, and the other map
+	 * will partially fill and then trigger overflow and need
+	 * bpf_seq_read restart.
+	 */
+	page_size = sysconf(_SC_PAGE_SIZE);
+
+	if (test_e2big_overflow) {
+		skel->rodata->print_len = (page_size + 8) / 8;
+		expected_read_len = 2 * (page_size + 8);
+	} else if (!ret1) {
+		skel->rodata->print_len = (page_size - 8) / 8;
+		expected_read_len = 2 * (page_size - 8);
+	} else {
+		skel->rodata->print_len = 1;
+		expected_read_len = 2 * 8;
+	}
+	skel->rodata->ret1 = ret1;
+
+	if (CHECK(bpf_iter_test_kern4__load(skel),
+		  "bpf_iter_test_kern4__load", "skeleton load failed\n"))
+		goto free_map2;
+
+	/* setup filtering map_id in bpf program */
+	map_info_len = sizeof(map_info);
+	err = bpf_obj_get_info_by_fd(map1_fd, &map_info, &map_info_len);
+	if (CHECK(err, "get_map_info", "get map info failed: %s\n",
+		  strerror(errno)))
+		goto free_map2;
+	skel->bss->map1_id = map_info.id;
+
+	err = bpf_obj_get_info_by_fd(map2_fd, &map_info, &map_info_len);
+	if (CHECK(err, "get_map_info", "get map info failed: %s\n",
+		  strerror(errno)))
+		goto free_map2;
+	skel->bss->map2_id = map_info.id;
+
+	link = bpf_program__attach_iter(skel->progs.dump_bpf_map, NULL);
+	if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
+		goto free_map2;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
+		goto free_link;
+
+	buf = malloc(expected_read_len);
+	if (!buf)
+		goto close_iter;
+
+	/* do read */
+	total_read_len = 0;
+	if (test_e2big_overflow) {
+		while ((len = read(iter_fd, buf, expected_read_len)) > 0)
+			total_read_len += len;
+
+		CHECK(len != -1 || errno != E2BIG, "read",
+		      "expected ret -1, errno E2BIG, but get ret %d, error %s\n",
+			  len, strerror(errno));
+		goto free_buf;
+	} else if (!ret1) {
+		while ((len = read(iter_fd, buf, expected_read_len)) > 0)
+			total_read_len += len;
+
+		if (CHECK(len < 0, "read", "read failed: %s\n",
+			  strerror(errno)))
+			goto free_buf;
+	} else {
+		do {
+			len = read(iter_fd, buf, expected_read_len);
+			if (len > 0)
+				total_read_len += len;
+		} while (len > 0 || len == -EAGAIN);
+
+		if (CHECK(len < 0, "read", "read failed: %s\n",
+			  strerror(errno)))
+			goto free_buf;
+	}
+
+	if (CHECK(total_read_len != expected_read_len, "read",
+		  "total len %u, expected len %u\n", total_read_len,
+		  expected_read_len))
+		goto free_buf;
+
+	if (CHECK(skel->bss->map1_accessed != 1, "map1_accessed",
+		  "expected 1 actual %d\n", skel->bss->map1_accessed))
+		goto free_buf;
+
+	if (CHECK(skel->bss->map2_accessed != 2, "map2_accessed",
+		  "expected 2 actual %d\n", skel->bss->map2_accessed))
+		goto free_buf;
+
+	CHECK(skel->bss->map2_seqnum1 != skel->bss->map2_seqnum2,
+	      "map2_seqnum", "two different seqnum %lld %lld\n",
+	      skel->bss->map2_seqnum1, skel->bss->map2_seqnum2);
+
+free_buf:
+	free(buf);
+close_iter:
+	close(iter_fd);
+free_link:
+	bpf_link__destroy(link);
+free_map2:
+	close(map2_fd);
+free_map1:
+	close(map1_fd);
+out:
+	bpf_iter_test_kern4__destroy(skel);
+}
+
+void test_bpf_iter(void)
+{
+	if (test__start_subtest("btf_id_or_null"))
+		test_btf_id_or_null();
+	if (test__start_subtest("ipv6_route"))
+		test_ipv6_route();
+	if (test__start_subtest("netlink"))
+		test_netlink();
+	if (test__start_subtest("bpf_map"))
+		test_bpf_map();
+	if (test__start_subtest("task"))
+		test_task();
+	if (test__start_subtest("task_file"))
+		test_task_file();
+	if (test__start_subtest("anon"))
+		test_anon_iter(false);
+	if (test__start_subtest("anon-read-one-char"))
+		test_anon_iter(true);
+	if (test__start_subtest("file"))
+		test_file_iter();
+	if (test__start_subtest("overflow"))
+		test_overflow(false, false);
+	if (test__start_subtest("overflow-e2big"))
+		test_overflow(true, false);
+	if (test__start_subtest("prog-ret-1"))
+		test_overflow(false, true);
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_map.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_map.c
new file mode 100644
index 000000000000..4867cd3445c8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_map.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("iter/bpf_map")
+int dump_bpf_map(struct bpf_iter__bpf_map *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	__u64 seq_num = ctx->meta->seq_num;
+	struct bpf_map *map = ctx->map;
+
+	if (map == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "      %%%%%% END %%%%%%\n");
+		return 0;
+	}
+
+	if (seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "      id   refcnt  usercnt  locked_vm\n");
+
+	BPF_SEQ_PRINTF(seq, "%8u %8ld %8ld %10lu\n", map->id, map->refcnt.counter,
+		       map->usercnt.counter,
+		       map->memory.user->locked_vm.counter);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c b/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c
new file mode 100644
index 000000000000..ab9e2650e021
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+extern bool CONFIG_IPV6_SUBTREES __kconfig __weak;
+
+#define RTF_GATEWAY		0x0002
+#define IFNAMSIZ		16
+#define fib_nh_gw_family	nh_common.nhc_gw_family
+#define fib_nh_gw6		nh_common.nhc_gw.ipv6
+#define fib_nh_dev		nh_common.nhc_dev
+
+SEC("iter/ipv6_route")
+int dump_ipv6_route(struct bpf_iter__ipv6_route *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct fib6_info *rt = ctx->rt;
+	const struct net_device *dev;
+	struct fib6_nh *fib6_nh;
+	unsigned int flags;
+	struct nexthop *nh;
+
+	if (rt == (void *)0)
+		return 0;
+
+	fib6_nh = &rt->fib6_nh[0];
+	flags = rt->fib6_flags;
+
+	/* FIXME: nexthop_is_multipath is not handled here. */
+	nh = rt->nh;
+	if (rt->nh)
+		fib6_nh = &nh->nh_info->fib6_nh;
+
+	BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
+
+	if (CONFIG_IPV6_SUBTREES)
+		BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_src.addr,
+			       rt->fib6_src.plen);
+	else
+		BPF_SEQ_PRINTF(seq, "00000000000000000000000000000000 00 ");
+
+	if (fib6_nh->fib_nh_gw_family) {
+		flags |= RTF_GATEWAY;
+		BPF_SEQ_PRINTF(seq, "%pi6 ", &fib6_nh->fib_nh_gw6);
+	} else {
+		BPF_SEQ_PRINTF(seq, "00000000000000000000000000000000 ");
+	}
+
+	dev = fib6_nh->fib_nh_dev;
+	if (dev)
+		BPF_SEQ_PRINTF(seq, "%08x %08x %08x %08x %8s\n", rt->fib6_metric,
+			       rt->fib6_ref.refs.counter, 0, flags, dev->name);
+	else
+		BPF_SEQ_PRINTF(seq, "%08x %08x %08x %08x\n", rt->fib6_metric,
+			       rt->fib6_ref.refs.counter, 0, flags);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_netlink.c b/tools/testing/selftests/bpf/progs/bpf_iter_netlink.c
new file mode 100644
index 000000000000..6b40a233d4e0
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_netlink.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+#define sk_rmem_alloc	sk_backlog.rmem_alloc
+#define sk_refcnt	__sk_common.skc_refcnt
+
+static inline struct inode *SOCK_INODE(struct socket *socket)
+{
+	return &container_of(socket, struct socket_alloc, socket)->vfs_inode;
+}
+
+SEC("iter/netlink")
+int dump_netlink(struct bpf_iter__netlink *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct netlink_sock *nlk = ctx->sk;
+	unsigned long group, ino;
+	struct inode *inode;
+	struct socket *sk;
+	struct sock *s;
+
+	if (nlk == (void *)0)
+		return 0;
+
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "sk               Eth Pid        Groups   "
+				    "Rmem     Wmem     Dump  Locks    Drops    "
+				    "Inode\n");
+
+	s = &nlk->sk;
+	BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
+
+	if (!nlk->groups)  {
+		group = 0;
+	} else {
+		/* FIXME: temporary use bpf_probe_read here, needs
+		 * verifier support to do direct access.
+		 */
+		bpf_probe_read(&group, sizeof(group), &nlk->groups[0]);
+	}
+	BPF_SEQ_PRINTF(seq, "%-10u %08x %-8d %-8d %-5d %-8d ",
+		       nlk->portid, (u32)group,
+		       s->sk_rmem_alloc.counter,
+		       s->sk_wmem_alloc.refs.counter - 1,
+		       nlk->cb_running, s->sk_refcnt.refs.counter);
+
+	sk = s->sk_socket;
+	if (!sk) {
+		ino = 0;
+	} else {
+		/* FIXME: container_of inside SOCK_INODE has a forced
+		 * type conversion, and direct access cannot be used
+		 * with current verifier.
+		 */
+		inode = SOCK_INODE(sk);
+		bpf_probe_read(&ino, sizeof(ino), &inode->i_ino);
+	}
+	BPF_SEQ_PRINTF(seq, "%-8u %-8lu\n", s->sk_drops.counter, ino);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task.c b/tools/testing/selftests/bpf/progs/bpf_iter_task.c
new file mode 100644
index 000000000000..90f9011c57ca
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("iter/task")
+int dump_task(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+
+	if (task == (void *)0) {
+		BPF_SEQ_PRINTF(seq, "    === END ===\n");
+		return 0;
+	}
+
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "    tgid      gid\n");
+
+	BPF_SEQ_PRINTF(seq, "%8d %8d\n", task->tgid, task->pid);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_file.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_file.c
new file mode 100644
index 000000000000..c6ced38f0880
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_file.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("iter/task_file")
+int dump_task_file(struct bpf_iter__task_file *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	__u32 fd = ctx->fd;
+	struct file *file = ctx->file;
+
+	if (task == (void *)0 || file == (void *)0)
+		return 0;
+
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(seq, "    tgid      gid       fd      file\n");
+
+	BPF_SEQ_PRINTF(seq, "%8d %8d %8d %lx\n", task->tgid, task->pid, fd,
+		       (long)file->f_op);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern1.c b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern1.c
new file mode 100644
index 000000000000..c71a7c283108
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern1.c
@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#define START_CHAR 'a'
+#include "bpf_iter_test_kern_common.h"
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern2.c b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern2.c
new file mode 100644
index 000000000000..8bdc8dc07444
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern2.c
@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#define START_CHAR 'A'
+#include "bpf_iter_test_kern_common.h"
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern3.c b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern3.c
new file mode 100644
index 000000000000..636a00fa074d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern3.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("iter/task")
+int dump_task(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	int tgid;
+
+	tgid = task->tgid;
+	bpf_seq_write(seq, &tgid, sizeof(tgid));
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern4.c b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern4.c
new file mode 100644
index 000000000000..b18dc0471d07
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern4.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u32 map1_id = 0, map2_id = 0;
+__u32 map1_accessed = 0, map2_accessed = 0;
+__u64 map1_seqnum = 0, map2_seqnum1 = 0, map2_seqnum2 = 0;
+
+static volatile const __u32 print_len;
+static volatile const __u32 ret1;
+
+SEC("iter/bpf_map")
+int dump_bpf_map(struct bpf_iter__bpf_map *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct bpf_map *map = ctx->map;
+	__u64 seq_num;
+	int i, ret = 0;
+
+	if (map == (void *)0)
+		return 0;
+
+	/* only dump map1_id and map2_id */
+	if (map->id != map1_id && map->id != map2_id)
+		return 0;
+
+	seq_num = ctx->meta->seq_num;
+	if (map->id == map1_id) {
+		map1_seqnum = seq_num;
+		map1_accessed++;
+	}
+
+	if (map->id == map2_id) {
+		if (map2_accessed == 0) {
+			map2_seqnum1 = seq_num;
+			if (ret1)
+				ret = 1;
+		} else {
+			map2_seqnum2 = seq_num;
+		}
+		map2_accessed++;
+	}
+
+	/* fill seq_file buffer */
+	for (i = 0; i < print_len; i++)
+		bpf_seq_write(seq, &seq_num, sizeof(seq_num));
+
+	return ret;
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern_common.h b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern_common.h
new file mode 100644
index 000000000000..bdd51cf14b54
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern_common.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2020 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+int count = 0;
+
+SEC("iter/task")
+int dump_task(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	char c;
+
+	if (count < 4) {
+		c = START_CHAR + count;
+		bpf_seq_write(seq, &c, sizeof(c));
+		count++;
+	}
+
+	return 0;
+}