Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted

Pull networking updates from Jakub Kicinski:
 "Core:

   - Add dedicated kmem_cache for typical/small skb->head, avoid having
     to access struct page at kfree time, and improve memory use.

   - Introduce sysctl to set default RPS configuration for new netdevs.

   - Define Netlink protocol specification format which can be used to
     describe messages used by each family and auto-generate parsers.
     Add tools for generating kernel data structures and uAPI headers.

   - Expose all net/core sysctls inside netns.

   - Remove 4s sleep in netpoll if carrier is instantly detected on
     boot.

   - Add configurable limit of MDB entries per port, and port-vlan.

   - Continue populating drop reasons throughout the stack.

   - Retire a handful of legacy Qdiscs and classifiers.

  Protocols:

   - Support IPv4 big TCP (TSO frames larger than 64kB).

   - Add IP_LOCAL_PORT_RANGE socket option, to control local port range
     on socket by socket basis.

   - Track and report in procfs number of MPTCP sockets used.

   - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
     manager.

   - IPv6: don't check net.ipv6.route.max_size and rely on garbage
     collection to free memory (similarly to IPv4).

   - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).

   - ICMP: add per-rate limit counters.

   - Add support for user scanning requests in ieee802154.

   - Remove static WEP support.

   - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
     reporting.

   - WiFi 7 EHT channel puncturing support (client & AP).

  BPF:

   - Add a rbtree data structure following the "next-gen data structure"
     precedent set by recently added linked list, that is, by using
     kfunc + kptr instead of adding a new BPF map type.

   - Expose XDP hints via kfuncs with initial support for RX hash and
     timestamp metadata.

   - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
     better support decap on GRE tunnel devices not operating in collect
     metadata.

   - Improve x86 JIT's codegen for PROBE_MEM runtime error checks.

   - Remove the need for trace_printk_lock for bpf_trace_printk and
     bpf_trace_vprintk helpers.

   - Extend libbpf's bpf_tracing.h support for tracing arguments of
     kprobes/uprobes and syscall as a special case.

   - Significantly reduce the search time for module symbols by
     livepatch and BPF.

   - Enable cpumasks to be used as kptrs, which is useful for tracing
     programs tracking which tasks end up running on which CPUs in
     different time intervals.

   - Add support for BPF trampoline on s390x and riscv64.

   - Add capability to export the XDP features supported by the NIC.

   - Add __bpf_kfunc tag for marking kernel functions as kfuncs.

   - Add cgroup.memory=nobpf kernel parameter option to disable BPF
     memory accounting for container environments.

  Netfilter:

   - Remove the CLUSTERIP target. It has been marked as obsolete for
     years, and we still have WARN splats wrt races of the out-of-band
     /proc interface installed by this target.

   - Add 'destroy' commands to nf_tables. They are identical to the
     existing 'delete' commands, but do not return an error if the
     referenced object (set, chain, rule...) did not exist.

  Driver API:

   - Improve cpumask_local_spread() locality to help NICs set the right
     IRQ affinity on AMD platforms.

   - Separate C22 and C45 MDIO bus transactions more clearly.

   - Introduce new DCB table to control DSCP rewrite on egress.

   - Support configuration of Physical Layer Collision Avoidance (PLCA)
     Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
     shared medium Ethernet.

   - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
     preemption of low priority frames by high priority frames.

   - Add support for controlling MACSec offload using netlink SET.

   - Rework devlink instance refcounts to allow registration and
     de-registration under the instance lock. Split the code into
     multiple files, drop some of the unnecessarily granular locks and
     factor out common parts of netlink operation handling.

   - Add TX frame aggregation parameters (for USB drivers).

   - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
     messages with notifications for debug.

   - Allow offloading of UDP NEW connections via act_ct.

   - Add support for per action HW stats in TC.

   - Support hardware miss to TC action (continue processing in SW from
     a specific point in the action chain).

   - Warn if old Wireless Extension user space interface is used with
     modern cfg80211/mac80211 drivers. Do not support Wireless
     Extensions for Wi-Fi 7 devices at all. Everyone should switch to
     using nl80211 interface instead.

   - Improve the CAN bit timing configuration. Use extack to return
     error messages directly to user space, update the SJW handling,
     including the definition of a new default value that will benefit
     CAN-FD controllers, by increasing their oscillator tolerance.

  New hardware / drivers:

   - Ethernet:
      - nVidia BlueField-3 support (control traffic driver)
      - Ethernet support for imx93 SoCs
      - Motorcomm yt8531 gigabit Ethernet PHY
      - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
      - Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
      - Amlogic gxl MDIO mux

   - WiFi:
      - RealTek RTL8188EU (rtl8xxxu)
      - Qualcomm Wi-Fi 7 devices (ath12k)

   - CAN:
      - Renesas R-Car V4H

  Drivers:

   - Bluetooth:
      - Set Per Platform Antenna Gain (PPAG) for Intel controllers.

   - Ethernet NICs:
      - Intel (1G, igc):
         - support TSN / Qbv / packet scheduling features of i226 model
      - Intel (100G, ice):
         - use GNSS subsystem instead of TTY
         - multi-buffer XDP support
         - extend support for GPIO pins to E823 devices
      - nVidia/Mellanox:
         - update the shared buffer configuration on PFC commands
         - implement PTP adjphase function for HW offset control
         - TC support for Geneve and GRE with VF tunnel offload
         - more efficient crypto key management method
         - multi-port eswitch support
      - Netronome/Corigine:
         - add DCB IEEE support
         - support IPsec offloading for NFP3800
      - Freescale/NXP (enetc):
         - support XDP_REDIRECT for XDP non-linear buffers
         - improve reconfig, avoid link flap and waiting for idle
         - support MAC Merge layer
      - Other NICs:
         - sfc/ef100: add basic devlink support for ef100
         - ionic: rx_push mode operation (writing descriptors via MMIO)
         - bnxt: use the auxiliary bus abstraction for RDMA
         - r8169: disable ASPM and reset bus in case of tx timeout
         - cpsw: support QSGMII mode for J721e CPSW9G
         - cpts: support pulse-per-second output
         - ngbe: add an mdio bus driver
         - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
         - r8152: handle devices with FW with NCM support
         - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
         - virtio-net: support multi buffer XDP
         - virtio/vsock: replace virtio_vsock_pkt with sk_buff
         - tsnep: XDP support

   - Ethernet high-speed switches:
      - nVidia/Mellanox (mlxsw):
         - add support for latency TLV (in FW control messages)
      - Microchip (sparx5):
         - separate explicit and implicit traffic forwarding rules, make
           the implicit rules always active
         - add support for egress DSCP rewrite
         - IS0 VCAP support (Ingress Classification)
         - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
           etc.)
         - ES2 VCAP support (Egress Access Control)
         - support for Per-Stream Filtering and Policing (802.1Q,
           8.6.5.1)

   - Ethernet embedded switches:
      - Marvell (mv88e6xxx):
         - add MAB (port auth) offload support
         - enable PTP receive for mv88e6390
      - NXP (ocelot):
         - support MAC Merge layer
         - support for the the vsc7512 internal copper phys
      - Microchip:
         - lan9303: convert to PHYLINK
         - lan966x: support TC flower filter statistics
         - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
         - lan937x: support Credit Based Shaper configuration
         - ksz9477: support Energy Efficient Ethernet
      - other:
         - qca8k: convert to regmap read/write API, use bulk operations
         - rswitch: Improve TX timestamp accuracy

   - Intel WiFi (iwlwifi):
      - EHT (Wi-Fi 7) rate reporting
      - STEP equalizer support: transfer some STEP (connection to radio
        on platforms with integrated wifi) related parameters from the
        BIOS to the firmware.

   - Qualcomm 802.11ax WiFi (ath11k):
      - IPQ5018 support
      - Fine Timing Measurement (FTM) responder role support
      - channel 177 support

   - MediaTek WiFi (mt76):
      - per-PHY LED support
      - mt7996: EHT (Wi-Fi 7) support
      - Wireless Ethernet Dispatch (WED) reset support
      - switch to using page pool allocator

   - RealTek WiFi (rtw89):
      - support new version of Bluetooth co-existance

   - Mobile:
      - rmnet: support TX aggregation"

* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
  page_pool: add a comment explaining the fragment counter usage
  net: ethtool: fix __ethtool_dev_mm_supported() implementation
  ethtool: pse-pd: Fix double word in comments
  xsk: add linux/vmalloc.h to xsk.c
  sefltests: netdevsim: wait for devlink instance after netns removal
  selftest: fib_tests: Always cleanup before exit
  net/mlx5e: Align IPsec ASO result memory to be as required by hardware
  net/mlx5e: TC, Set CT miss to the specific ct action instance
  net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
  net/mlx5: Refactor tc miss handling to a single function
  net/mlx5: Kconfig: Make tc offload depend on tc skb extension
  net/sched: flower: Support hardware miss to tc action
  net/sched: flower: Move filter handle initialization earlier
  net/sched: cls_api: Support hardware miss to tc action
  net/sched: Rename user cookie and act cookie
  sfc: fix builds without CONFIG_RTC_LIB
  sfc: clean up some inconsistent indentings
  net/mlx4_en: Introduce flexible array to silence overflow warning
  net: lan966x: Fix possible deadlock inside PTP
  net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
  ...

1 files changed, 485 insertions, 0 deletions

diff --git a/Documentation/bpf/bpf_iterators.rst b/Documentation/bpf/bpf_iterators.rst
new file mode 100644
index 000000000..6d7770793
--- /dev/null
+++ b/Documentation/bpf/bpf_iterators.rst
@@ -0,0 +1,485 @@
+=============
+BPF Iterators
+=============
+
+
+----------
+Motivation
+----------
+
+There are a few existing ways to dump kernel data into user space. The most
+popular one is the ``/proc`` system. For example, ``cat /proc/net/tcp6`` dumps
+all tcp6 sockets in the system, and ``cat /proc/net/netlink`` dumps all netlink
+sockets in the system. However, their output format tends to be fixed, and if
+users want more information about these sockets, they have to patch the kernel,
+which often takes time to publish upstream and release. The same is true for popular
+tools like `ss <https://man7.org/linux/man-pages/man8/ss.8.html>`_ where any
+additional information needs a kernel patch.
+
+To solve this problem, the `drgn
+<https://www.kernel.org/doc/html/latest/bpf/drgn.html>`_ tool is often used to
+dig out the kernel data with no kernel change. However, the main drawback for
+drgn is performance, as it cannot do pointer tracing inside the kernel. In
+addition, drgn cannot validate a pointer value and may read invalid data if the
+pointer becomes invalid inside the kernel.
+
+The BPF iterator solves the above problem by providing flexibility on what data
+(e.g., tasks, bpf_maps, etc.) to collect by calling BPF programs for each kernel
+data object.
+
+----------------------
+How BPF Iterators Work
+----------------------
+
+A BPF iterator is a type of BPF program that allows users to iterate over
+specific types of kernel objects. Unlike traditional BPF tracing programs that
+allow users to define callbacks that are invoked at particular points of
+execution in the kernel, BPF iterators allow users to define callbacks that
+should be executed for every entry in a variety of kernel data structures.
+
+For example, users can define a BPF iterator that iterates over every task on
+the system and dumps the total amount of CPU runtime currently used by each of
+them. Another BPF task iterator may instead dump the cgroup information for each
+task. Such flexibility is the core value of BPF iterators.
+
+A BPF program is always loaded into the kernel at the behest of a user space
+process. A user space process loads a BPF program by opening and initializing
+the program skeleton as required and then invoking a syscall to have the BPF
+program verified and loaded by the kernel.
+
+In traditional tracing programs, a program is activated by having user space
+obtain a ``bpf_link`` to the program with ``bpf_program__attach()``. Once
+activated, the program callback will be invoked whenever the tracepoint is
+triggered in the main kernel. For BPF iterator programs, a ``bpf_link`` to the
+program is obtained using ``bpf_link_create()``, and the program callback is
+invoked by issuing system calls from user space.
+
+Next, let us see how you can use the iterators to iterate on kernel objects and
+read data.
+
+------------------------
+How to Use BPF iterators
+------------------------
+
+BPF selftests are a great resource to illustrate how to use the iterators. In
+this section, we’ll walk through a BPF selftest which shows how to load and use
+a BPF iterator program.   To begin, we’ll look at `bpf_iter.c
+<https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/prog_tests/bpf_iter.c>`_,
+which illustrates how to load and trigger BPF iterators on the user space side.
+Later, we’ll look at a BPF program that runs in kernel space.
+
+Loading a BPF iterator in the kernel from user space typically involves the
+following steps:
+
+* The BPF program is loaded into the kernel through ``libbpf``. Once the kernel
+  has verified and loaded the program, it returns a file descriptor (fd) to user
+  space.
+* Obtain a ``link_fd`` to the BPF program by calling the ``bpf_link_create()``
+  specified with the BPF program file descriptor received from the kernel.
+* Next, obtain a BPF iterator file descriptor (``bpf_iter_fd``) by calling the
+  ``bpf_iter_create()`` specified with the ``bpf_link`` received from Step 2.
+* Trigger the iteration by calling ``read(bpf_iter_fd)`` until no data is
+  available.
+* Close the iterator fd using ``close(bpf_iter_fd)``.
+* If needed to reread the data, get a new ``bpf_iter_fd`` and do the read again.
+
+The following are a few examples of selftest BPF iterator programs:
+
+* `bpf_iter_tcp4.c <https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/bpf_iter_tcp4.c>`_
+* `bpf_iter_task_vma.c <https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/bpf_iter_task_vma.c>`_
+* `bpf_iter_task_file.c <https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/bpf_iter_task_file.c>`_
+
+Let us look at ``bpf_iter_task_file.c``, which runs in kernel space:
+
+Here is the definition of ``bpf_iter__task_file`` in `vmlinux.h
+<https://facebookmicrosites.github.io/bpf/blog/2020/02/19/bpf-portability-and-co-re.html#btf>`_.
+Any struct name in ``vmlinux.h`` in the format ``bpf_iter__<iter_name>``
+represents a BPF iterator. The suffix ``<iter_name>`` represents the type of
+iterator.
+
+::
+
+    struct bpf_iter__task_file {
+            union {
+                struct bpf_iter_meta *meta;
+            };
+            union {
+                struct task_struct *task;
+            };
+            u32 fd;
+            union {
+                struct file *file;
+            };
+    };
+
+In the above code, the field 'meta' contains the metadata, which is the same for
+all BPF iterator programs. The rest of the fields are specific to different
+iterators. For example, for task_file iterators, the kernel layer provides the
+'task', 'fd' and 'file' field values. The 'task' and 'file' are `reference
+counted
+<https://facebookmicrosites.github.io/bpf/blog/2018/08/31/object-lifetime.html#file-descriptors-and-reference-counters>`_,
+so they won't go away when the BPF program runs.
+
+Here is a snippet from the  ``bpf_iter_task_file.c`` file:
+
+::
+
+  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;
+    struct file *file = ctx->file;
+    __u32 fd = ctx->fd;
+
+    if (task == NULL || file == NULL)
+      return 0;
+
+    if (ctx->meta->seq_num == 0) {
+      count = 0;
+      BPF_SEQ_PRINTF(seq, "    tgid      gid       fd      file\n");
+    }
+
+    if (tgid == task->tgid && task->tgid != task->pid)
+      count++;
+
+    if (last_tgid != task->tgid) {
+      last_tgid = task->tgid;
+      unique_tgid_count++;
+    }
+
+    BPF_SEQ_PRINTF(seq, "%8d %8d %8d %lx\n", task->tgid, task->pid, fd,
+            (long)file->f_op);
+    return 0;
+  }
+
+In the above example, the section name ``SEC(iter/task_file)``, indicates that
+the program is a BPF iterator program to iterate all files from all tasks. The
+context of the program is ``bpf_iter__task_file`` struct.
+
+The user space program invokes the BPF iterator program running in the kernel
+by issuing a ``read()`` syscall. Once invoked, the BPF
+program can export data to user space using a variety of BPF helper functions.
+You can use either ``bpf_seq_printf()`` (and BPF_SEQ_PRINTF helper macro) or
+``bpf_seq_write()`` function based on whether you need formatted output or just
+binary data, respectively. For binary-encoded data, the user space applications
+can process the data from ``bpf_seq_write()`` as needed. For the formatted data,
+you can use ``cat <path>`` to print the results similar to ``cat
+/proc/net/netlink`` after pinning the BPF iterator to the bpffs mount. Later,
+use  ``rm -f <path>`` to remove the pinned iterator.
+
+For example, you can use the following command to create a BPF iterator from the
+``bpf_iter_ipv6_route.o`` object file and pin it to the ``/sys/fs/bpf/my_route``
+path:
+
+::
+
+  $ bpftool iter pin ./bpf_iter_ipv6_route.o  /sys/fs/bpf/my_route
+
+And then print out the results using the following command:
+
+::
+
+  $ cat /sys/fs/bpf/my_route
+
+
+-------------------------------------------------------
+Implement Kernel Support for BPF Iterator Program Types
+-------------------------------------------------------
+
+To implement a BPF iterator in the kernel, the developer must make a one-time
+change to the following key data structure defined in the `bpf.h
+<https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/include/linux/bpf.h>`_
+file.
+
+::
+
+  struct bpf_iter_reg {
+            const char *target;
+            bpf_iter_attach_target_t attach_target;
+            bpf_iter_detach_target_t detach_target;
+            bpf_iter_show_fdinfo_t show_fdinfo;
+            bpf_iter_fill_link_info_t fill_link_info;
+            bpf_iter_get_func_proto_t get_func_proto;
+            u32 ctx_arg_info_size;
+            u32 feature;
+            struct bpf_ctx_arg_aux ctx_arg_info[BPF_ITER_CTX_ARG_MAX];
+            const struct bpf_iter_seq_info *seq_info;
+  };
+
+After filling the data structure fields, call ``bpf_iter_reg_target()`` to
+register the iterator to the main BPF iterator subsystem.
+
+The following is the breakdown for each field in struct ``bpf_iter_reg``.
+
+.. list-table::
+   :widths: 25 50
+   :header-rows: 1
+
+   * - Fields
+     - Description
+   * - target
+     - Specifies the name of the BPF iterator. For example: ``bpf_map``,
+       ``bpf_map_elem``. The name should be different from other ``bpf_iter`` target names in the kernel.
+   * - attach_target and detach_target
+     - Allows for target specific ``link_create`` action since some targets
+       may need special processing. Called during the user space link_create stage.
+   * - show_fdinfo and fill_link_info
+     - Called to fill target specific information when user tries to get link
+       info associated with the iterator.
+   * - get_func_proto
+     - Permits a BPF iterator to access BPF helpers specific to the iterator.
+   * - ctx_arg_info_size and ctx_arg_info
+     - Specifies the verifier states for BPF program arguments associated with
+       the bpf iterator.
+   * - feature
+     - Specifies certain action requests in the kernel BPF iterator
+       infrastructure. Currently, only BPF_ITER_RESCHED is supported. This means
+       that the kernel function cond_resched() is called to avoid other kernel
+       subsystem (e.g., rcu) misbehaving.
+   * - seq_info
+     - Specifies certain action requests in the kernel BPF iterator
+       infrastructure. Currently, only BPF_ITER_RESCHED is supported. This means
+       that the kernel function cond_resched() is called to avoid other kernel
+       subsystem (e.g., rcu) misbehaving.
+
+
+`Click here
+<https://lore.kernel.org/bpf/20210212183107.50963-2-songliubraving@fb.com/>`_
+to see an implementation of the ``task_vma`` BPF iterator in the kernel.
+
+---------------------------------
+Parameterizing BPF Task Iterators
+---------------------------------
+
+By default, BPF iterators walk through all the objects of the specified types
+(processes, cgroups, maps, etc.) across the entire system to read relevant
+kernel data. But often, there are cases where we only care about a much smaller
+subset of iterable kernel objects, such as only iterating tasks within a
+specific process. Therefore, BPF iterator programs support filtering out objects
+from iteration by allowing user space to configure the iterator program when it
+is attached.
+
+--------------------------
+BPF Task Iterator Program
+--------------------------
+
+The following code is a BPF iterator program to print files and task information
+through the ``seq_file`` of the iterator. It is a standard BPF iterator program
+that visits every file of an iterator. We will use this BPF program in our
+example later.
+
+::
+
+  #include <vmlinux.h>
+  #include <bpf/bpf_helpers.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;
+        struct file *file = ctx->file;
+        __u32 fd = ctx->fd;
+        if (task == NULL || file == NULL)
+                return 0;
+        if (ctx->meta->seq_num == 0) {
+                BPF_SEQ_PRINTF(seq, "    tgid      pid       fd      file\n");
+        }
+        BPF_SEQ_PRINTF(seq, "%8d %8d %8d %lx\n", task->tgid, task->pid, fd,
+                        (long)file->f_op);
+        return 0;
+  }
+
+----------------------------------------
+Creating a File Iterator with Parameters
+----------------------------------------
+
+Now, let us look at how to create an iterator that includes only files of a
+process.
+
+First,  fill the ``bpf_iter_attach_opts`` struct as shown below:
+
+::
+
+  LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+  union bpf_iter_link_info linfo;
+  memset(&linfo, 0, sizeof(linfo));
+  linfo.task.pid = getpid();
+  opts.link_info = &linfo;
+  opts.link_info_len = sizeof(linfo);
+
+``linfo.task.pid``, if it is non-zero, directs the kernel to create an iterator
+that only includes opened files for the process with the specified ``pid``. In
+this example, we will only be iterating files for our process. If
+``linfo.task.pid`` is zero, the iterator will visit every opened file of every
+process. Similarly, ``linfo.task.tid`` directs the kernel to create an iterator
+that visits opened files of a specific thread, not a process. In this example,
+``linfo.task.tid`` is different from ``linfo.task.pid`` only if the thread has a
+separate file descriptor table. In most circumstances, all process threads share
+a single file descriptor table.
+
+Now, in the userspace program, pass the pointer of struct to the
+``bpf_program__attach_iter()``.
+
+::
+
+  link = bpf_program__attach_iter(prog, &opts); iter_fd =
+  bpf_iter_create(bpf_link__fd(link));
+
+If both *tid* and *pid* are zero, an iterator created from this struct
+``bpf_iter_attach_opts`` will include every opened file of every task in the
+system (in the namespace, actually.) It is the same as passing a NULL as the
+second argument to ``bpf_program__attach_iter()``.
+
+The whole program looks like the following code:
+
+::
+
+  #include <stdio.h>
+  #include <unistd.h>
+  #include <bpf/bpf.h>
+  #include <bpf/libbpf.h>
+  #include "bpf_iter_task_ex.skel.h"
+
+  static int do_read_opts(struct bpf_program *prog, struct bpf_iter_attach_opts *opts)
+  {
+        struct bpf_link *link;
+        char buf[16] = {};
+        int iter_fd = -1, len;
+        int ret = 0;
+
+        link = bpf_program__attach_iter(prog, opts);
+        if (!link) {
+                fprintf(stderr, "bpf_program__attach_iter() fails\n");
+                return -1;
+        }
+        iter_fd = bpf_iter_create(bpf_link__fd(link));
+        if (iter_fd < 0) {
+                fprintf(stderr, "bpf_iter_create() fails\n");
+                ret = -1;
+                goto free_link;
+        }
+        /* not check contents, but ensure read() ends without error */
+        while ((len = read(iter_fd, buf, sizeof(buf) - 1)) > 0) {
+                buf[len] = 0;
+                printf("%s", buf);
+        }
+        printf("\n");
+  free_link:
+        if (iter_fd >= 0)
+                close(iter_fd);
+        bpf_link__destroy(link);
+        return 0;
+  }
+
+  static void test_task_file(void)
+  {
+        LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+        struct bpf_iter_task_ex *skel;
+        union bpf_iter_link_info linfo;
+        skel = bpf_iter_task_ex__open_and_load();
+        if (skel == NULL)
+                return;
+        memset(&linfo, 0, sizeof(linfo));
+        linfo.task.pid = getpid();
+        opts.link_info = &linfo;
+        opts.link_info_len = sizeof(linfo);
+        printf("PID %d\n", getpid());
+        do_read_opts(skel->progs.dump_task_file, &opts);
+        bpf_iter_task_ex__destroy(skel);
+  }
+
+  int main(int argc, const char * const * argv)
+  {
+        test_task_file();
+        return 0;
+  }
+
+The following lines are the output of the program.
+::
+
+  PID 1859
+
+     tgid      pid       fd      file
+     1859     1859        0 ffffffff82270aa0
+     1859     1859        1 ffffffff82270aa0
+     1859     1859        2 ffffffff82270aa0
+     1859     1859        3 ffffffff82272980
+     1859     1859        4 ffffffff8225e120
+     1859     1859        5 ffffffff82255120
+     1859     1859        6 ffffffff82254f00
+     1859     1859        7 ffffffff82254d80
+     1859     1859        8 ffffffff8225abe0
+
+------------------
+Without Parameters
+------------------
+
+Let us look at how a BPF iterator without parameters skips files of other
+processes in the system. In this case, the BPF program has to check the pid or
+the tid of tasks, or it will receive every opened file in the system (in the
+current *pid* namespace, actually). So, we usually add a global variable in the
+BPF program to pass a *pid* to the BPF program.
+
+The BPF program would look like the following block.
+
+  ::
+
+    ......
+    int target_pid = 0;
+
+    SEC("iter/task_file")
+    int dump_task_file(struct bpf_iter__task_file *ctx)
+    {
+          ......
+          if (task->tgid != target_pid) /* Check task->pid instead to check thread IDs */
+                  return 0;
+          BPF_SEQ_PRINTF(seq, "%8d %8d %8d %lx\n", task->tgid, task->pid, fd,
+                          (long)file->f_op);
+          return 0;
+    }
+
+The user space program would look like the following block:
+
+  ::
+
+    ......
+    static void test_task_file(void)
+    {
+          ......
+          skel = bpf_iter_task_ex__open_and_load();
+          if (skel == NULL)
+                  return;
+          skel->bss->target_pid = getpid(); /* process ID.  For thread id, use gettid() */
+          memset(&linfo, 0, sizeof(linfo));
+          linfo.task.pid = getpid();
+          opts.link_info = &linfo;
+          opts.link_info_len = sizeof(linfo);
+          ......
+    }
+
+``target_pid`` is a global variable in the BPF program. The user space program
+should initialize the variable with a process ID to skip opened files of other
+processes in the BPF program. When you parametrize a BPF iterator, the iterator
+calls the BPF program fewer times which can save significant resources.
+
+---------------------------
+Parametrizing VMA Iterators
+---------------------------
+
+By default, a BPF VMA iterator includes every VMA in every process.  However,
+you can still specify a process or a thread to include only its VMAs. Unlike
+files, a thread can not have a separate address space (since Linux 2.6.0-test6).
+Here, using *tid* makes no difference from using *pid*.
+
+----------------------------
+Parametrizing Task Iterators
+----------------------------
+
+A BPF task iterator with *pid* includes all tasks (threads) of a process. The
+BPF program receives these tasks one after another. You can specify a BPF task
+iterator with *tid* parameter to include only the tasks that match the given
+*tid*.