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, 478 insertions, 0 deletions

diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
new file mode 100644
index 000000000..5f6454b9d
--- /dev/null
+++ b/Documentation/fault-injection/fault-injection.rst
@@ -0,0 +1,478 @@
+===========================================
+Fault injection capabilities infrastructure
+===========================================
+
+See also drivers/md/md-faulty.c and "every_nth" module option for scsi_debug.
+
+
+Available fault injection capabilities
+--------------------------------------
+
+- failslab
+
+  injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
+
+- fail_page_alloc
+
+  injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
+
+- fail_usercopy
+
+  injects failures in user memory access functions. (copy_from_user(), get_user(), ...)
+
+- fail_futex
+
+  injects futex deadlock and uaddr fault errors.
+
+- fail_sunrpc
+
+  injects kernel RPC client and server failures.
+
+- fail_make_request
+
+  injects disk IO errors on devices permitted by setting
+  /sys/block/<device>/make-it-fail or
+  /sys/block/<device>/<partition>/make-it-fail. (submit_bio_noacct())
+
+- fail_mmc_request
+
+  injects MMC data errors on devices permitted by setting
+  debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
+
+- fail_function
+
+  injects error return on specific functions, which are marked by
+  ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
+  under /sys/kernel/debug/fail_function. No boot option supported.
+
+- NVMe fault injection
+
+  inject NVMe status code and retry flag on devices permitted by setting
+  debugfs entries under /sys/kernel/debug/nvme*/fault_inject. The default
+  status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
+  retry flag can be set via the debugfs.
+
+
+Configure fault-injection capabilities behavior
+-----------------------------------------------
+
+debugfs entries
+^^^^^^^^^^^^^^^
+
+fault-inject-debugfs kernel module provides some debugfs entries for runtime
+configuration of fault-injection capabilities.
+
+- /sys/kernel/debug/fail*/probability:
+
+	likelihood of failure injection, in percent.
+
+	Format: <percent>
+
+	Note that one-failure-per-hundred is a very high error rate
+	for some testcases.  Consider setting probability=100 and configure
+	/sys/kernel/debug/fail*/interval for such testcases.
+
+- /sys/kernel/debug/fail*/interval:
+
+	specifies the interval between failures, for calls to
+	should_fail() that pass all the other tests.
+
+	Note that if you enable this, by setting interval>1, you will
+	probably want to set probability=100.
+
+- /sys/kernel/debug/fail*/times:
+
+	specifies how many times failures may happen at most. A value of -1
+	means "no limit".
+
+- /sys/kernel/debug/fail*/space:
+
+	specifies an initial resource "budget", decremented by "size"
+	on each call to should_fail(,size).  Failure injection is
+	suppressed until "space" reaches zero.
+
+- /sys/kernel/debug/fail*/verbose
+
+	Format: { 0 | 1 | 2 }
+
+	specifies the verbosity of the messages when failure is
+	injected.  '0' means no messages; '1' will print only a single
+	log line per failure; '2' will print a call trace too -- useful
+	to debug the problems revealed by fault injection.
+
+- /sys/kernel/debug/fail*/task-filter:
+
+	Format: { 'Y' | 'N' }
+
+	A value of 'N' disables filtering by process (default).
+	Any positive value limits failures to only processes indicated by
+	/proc/<pid>/make-it-fail==1.
+
+- /sys/kernel/debug/fail*/require-start,
+  /sys/kernel/debug/fail*/require-end,
+  /sys/kernel/debug/fail*/reject-start,
+  /sys/kernel/debug/fail*/reject-end:
+
+	specifies the range of virtual addresses tested during
+	stacktrace walking.  Failure is injected only if some caller
+	in the walked stacktrace lies within the required range, and
+	none lies within the rejected range.
+	Default required range is [0,ULONG_MAX) (whole of virtual address space).
+	Default rejected range is [0,0).
+
+- /sys/kernel/debug/fail*/stacktrace-depth:
+
+	specifies the maximum stacktrace depth walked during search
+	for a caller within [require-start,require-end) OR
+	[reject-start,reject-end).
+
+- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'Y', setting it to 'N' will also inject failures into
+	highmem/user allocations (__GFP_HIGHMEM allocations).
+
+- /sys/kernel/debug/failslab/ignore-gfp-wait:
+- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'Y', setting it to 'N' will also inject failures
+	into allocations that can sleep (__GFP_DIRECT_RECLAIM allocations).
+
+- /sys/kernel/debug/fail_page_alloc/min-order:
+
+	specifies the minimum page allocation order to be injected
+	failures.
+
+- /sys/kernel/debug/fail_futex/ignore-private:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'N', setting it to 'Y' will disable failure injections
+	when dealing with private (address space) futexes.
+
+- /sys/kernel/debug/fail_sunrpc/ignore-client-disconnect:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'N', setting it to 'Y' will disable disconnect
+	injection on the RPC client.
+
+- /sys/kernel/debug/fail_sunrpc/ignore-server-disconnect:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'N', setting it to 'Y' will disable disconnect
+	injection on the RPC server.
+
+- /sys/kernel/debug/fail_sunrpc/ignore-cache-wait:
+
+	Format: { 'Y' | 'N' }
+
+	default is 'N', setting it to 'Y' will disable cache wait
+	injection on the RPC server.
+
+- /sys/kernel/debug/fail_function/inject:
+
+	Format: { 'function-name' | '!function-name' | '' }
+
+	specifies the target function of error injection by name.
+	If the function name leads '!' prefix, given function is
+	removed from injection list. If nothing specified ('')
+	injection list is cleared.
+
+- /sys/kernel/debug/fail_function/injectable:
+
+	(read only) shows error injectable functions and what type of
+	error values can be specified. The error type will be one of
+	below;
+	- NULL:	retval must be 0.
+	- ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
+	- ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).
+
+- /sys/kernel/debug/fail_function/<function-name>/retval:
+
+	specifies the "error" return value to inject to the given function.
+	This will be created when the user specifies a new injection entry.
+	Note that this file only accepts unsigned values. So, if you want to
+	use a negative errno, you better use 'printf' instead of 'echo', e.g.:
+	$ printf %#x -12 > retval
+
+Boot option
+^^^^^^^^^^^
+
+In order to inject faults while debugfs is not available (early boot time),
+use the boot option::
+
+	failslab=
+	fail_page_alloc=
+	fail_usercopy=
+	fail_make_request=
+	fail_futex=
+	mmc_core.fail_request=<interval>,<probability>,<space>,<times>
+
+proc entries
+^^^^^^^^^^^^
+
+- /proc/<pid>/fail-nth,
+  /proc/self/task/<tid>/fail-nth:
+
+	Write to this file of integer N makes N-th call in the task fail.
+	Read from this file returns a integer value. A value of '0' indicates
+	that the fault setup with a previous write to this file was injected.
+	A positive integer N indicates that the fault wasn't yet injected.
+	Note that this file enables all types of faults (slab, futex, etc).
+	This setting takes precedence over all other generic debugfs settings
+	like probability, interval, times, etc. But per-capability settings
+	(e.g. fail_futex/ignore-private) take precedence over it.
+
+	This feature is intended for systematic testing of faults in a single
+	system call. See an example below.
+
+How to add new fault injection capability
+-----------------------------------------
+
+- #include <linux/fault-inject.h>
+
+- define the fault attributes
+
+  DECLARE_FAULT_ATTR(name);
+
+  Please see the definition of struct fault_attr in fault-inject.h
+  for details.
+
+- provide a way to configure fault attributes
+
+- boot option
+
+  If you need to enable the fault injection capability from boot time, you can
+  provide boot option to configure it. There is a helper function for it:
+
+	setup_fault_attr(attr, str);
+
+- debugfs entries
+
+  failslab, fail_page_alloc, fail_usercopy, and fail_make_request use this way.
+  Helper functions:
+
+	fault_create_debugfs_attr(name, parent, attr);
+
+- module parameters
+
+  If the scope of the fault injection capability is limited to a
+  single kernel module, it is better to provide module parameters to
+  configure the fault attributes.
+
+- add a hook to insert failures
+
+  Upon should_fail() returning true, client code should inject a failure:
+
+	should_fail(attr, size);
+
+Application Examples
+--------------------
+
+- Inject slab allocation failures into module init/exit code::
+
+    #!/bin/bash
+
+    FAILTYPE=failslab
+    echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
+    echo 10 > /sys/kernel/debug/$FAILTYPE/probability
+    echo 100 > /sys/kernel/debug/$FAILTYPE/interval
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo 0 > /sys/kernel/debug/$FAILTYPE/space
+    echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
+    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
+
+    faulty_system()
+    {
+	bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
+    }
+
+    if [ $# -eq 0 ]
+    then
+	echo "Usage: $0 modulename [ modulename ... ]"
+	exit 1
+    fi
+
+    for m in $*
+    do
+	echo inserting $m...
+	faulty_system modprobe $m
+
+	echo removing $m...
+	faulty_system modprobe -r $m
+    done
+
+------------------------------------------------------------------------------
+
+- Inject page allocation failures only for a specific module::
+
+    #!/bin/bash
+
+    FAILTYPE=fail_page_alloc
+    module=$1
+
+    if [ -z $module ]
+    then
+	echo "Usage: $0 <modulename>"
+	exit 1
+    fi
+
+    modprobe $module
+
+    if [ ! -d /sys/module/$module/sections ]
+    then
+	echo Module $module is not loaded
+	exit 1
+    fi
+
+    cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
+    cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
+
+    echo N > /sys/kernel/debug/$FAILTYPE/task-filter
+    echo 10 > /sys/kernel/debug/$FAILTYPE/probability
+    echo 100 > /sys/kernel/debug/$FAILTYPE/interval
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo 0 > /sys/kernel/debug/$FAILTYPE/space
+    echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
+    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
+    echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
+    echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
+
+    trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
+
+    echo "Injecting errors into the module $module... (interrupt to stop)"
+    sleep 1000000
+
+------------------------------------------------------------------------------
+
+- Inject open_ctree error while btrfs mount::
+
+    #!/bin/bash
+
+    rm -f testfile.img
+    dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
+    DEVICE=$(losetup --show -f testfile.img)
+    mkfs.btrfs -f $DEVICE
+    mkdir -p tmpmnt
+
+    FAILTYPE=fail_function
+    FAILFUNC=open_ctree
+    echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
+    printf %#x -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
+    echo N > /sys/kernel/debug/$FAILTYPE/task-filter
+    echo 100 > /sys/kernel/debug/$FAILTYPE/probability
+    echo 0 > /sys/kernel/debug/$FAILTYPE/interval
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo 0 > /sys/kernel/debug/$FAILTYPE/space
+    echo 1 > /sys/kernel/debug/$FAILTYPE/verbose
+
+    mount -t btrfs $DEVICE tmpmnt
+    if [ $? -ne 0 ]
+    then
+	echo "SUCCESS!"
+    else
+	echo "FAILED!"
+	umount tmpmnt
+    fi
+
+    echo > /sys/kernel/debug/$FAILTYPE/inject
+
+    rmdir tmpmnt
+    losetup -d $DEVICE
+    rm testfile.img
+
+
+Tool to run command with failslab or fail_page_alloc
+----------------------------------------------------
+In order to make it easier to accomplish the tasks mentioned above, we can use
+tools/testing/fault-injection/failcmd.sh.  Please run a command
+"./tools/testing/fault-injection/failcmd.sh --help" for more information and
+see the following examples.
+
+Examples:
+
+Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
+allocation failure::
+
+	# ./tools/testing/fault-injection/failcmd.sh \
+		-- make -C tools/testing/selftests/ run_tests
+
+Same as above except to specify 100 times failures at most instead of one time
+at most by default::
+
+	# ./tools/testing/fault-injection/failcmd.sh --times=100 \
+		-- make -C tools/testing/selftests/ run_tests
+
+Same as above except to inject page allocation failure instead of slab
+allocation failure::
+
+	# env FAILCMD_TYPE=fail_page_alloc \
+		./tools/testing/fault-injection/failcmd.sh --times=100 \
+		-- make -C tools/testing/selftests/ run_tests
+
+Systematic faults using fail-nth
+---------------------------------
+
+The following code systematically faults 0-th, 1-st, 2-nd and so on
+capabilities in the socketpair() system call::
+
+  #include <sys/types.h>
+  #include <sys/stat.h>
+  #include <sys/socket.h>
+  #include <sys/syscall.h>
+  #include <fcntl.h>
+  #include <unistd.h>
+  #include <string.h>
+  #include <stdlib.h>
+  #include <stdio.h>
+  #include <errno.h>
+
+  int main()
+  {
+	int i, err, res, fail_nth, fds[2];
+	char buf[128];
+
+	system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
+	sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
+	fail_nth = open(buf, O_RDWR);
+	for (i = 1;; i++) {
+		sprintf(buf, "%d", i);
+		write(fail_nth, buf, strlen(buf));
+		res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
+		err = errno;
+		pread(fail_nth, buf, sizeof(buf), 0);
+		if (res == 0) {
+			close(fds[0]);
+			close(fds[1]);
+		}
+		printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
+			res, err);
+		if (atoi(buf))
+			break;
+	}
+	return 0;
+  }
+
+An example output::
+
+	1-th fault Y: res=-1/23
+	2-th fault Y: res=-1/23
+	3-th fault Y: res=-1/12
+	4-th fault Y: res=-1/12
+	5-th fault Y: res=-1/23
+	6-th fault Y: res=-1/23
+	7-th fault Y: res=-1/23
+	8-th fault Y: res=-1/12
+	9-th fault Y: res=-1/12
+	10-th fault Y: res=-1/12
+	11-th fault Y: res=-1/12
+	12-th fault Y: res=-1/12
+	13-th fault Y: res=-1/12
+	14-th fault Y: res=-1/12
+	15-th fault Y: res=-1/12
+	16-th fault N: res=0/12