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, 531 insertions, 0 deletions

diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
new file mode 100644
index 000000000..663a047f7
--- /dev/null
+++ b/tools/tracing/rtla/src/utils.c
@@ -0,0 +1,531 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Red Hat Inc, Daniel Bristot de Oliveira <bristot@kernel.org>
+ */
+
+#include <dirent.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+
+#include "utils.h"
+
+#define MAX_MSG_LENGTH	1024
+int config_debug;
+
+/*
+ * err_msg - print an error message to the stderr
+ */
+void err_msg(const char *fmt, ...)
+{
+	char message[MAX_MSG_LENGTH];
+	va_list ap;
+
+	va_start(ap, fmt);
+	vsnprintf(message, sizeof(message), fmt, ap);
+	va_end(ap);
+
+	fprintf(stderr, "%s", message);
+}
+
+/*
+ * debug_msg - print a debug message to stderr if debug is set
+ */
+void debug_msg(const char *fmt, ...)
+{
+	char message[MAX_MSG_LENGTH];
+	va_list ap;
+
+	if (!config_debug)
+		return;
+
+	va_start(ap, fmt);
+	vsnprintf(message, sizeof(message), fmt, ap);
+	va_end(ap);
+
+	fprintf(stderr, "%s", message);
+}
+
+/*
+ * get_llong_from_str - get a long long int from a string
+ */
+long long get_llong_from_str(char *start)
+{
+	long long value;
+	char *end;
+
+	errno = 0;
+	value = strtoll(start, &end, 10);
+	if (errno || start == end)
+		return -1;
+
+	return value;
+}
+
+/*
+ * get_duration - fill output with a human readable duration since start_time
+ */
+void get_duration(time_t start_time, char *output, int output_size)
+{
+	time_t now = time(NULL);
+	struct tm *tm_info;
+	time_t duration;
+
+	duration = difftime(now, start_time);
+	tm_info = gmtime(&duration);
+
+	snprintf(output, output_size, "%3d %02d:%02d:%02d",
+			tm_info->tm_yday,
+			tm_info->tm_hour,
+			tm_info->tm_min,
+			tm_info->tm_sec);
+}
+
+/*
+ * parse_cpu_list - parse a cpu_list filling a char vector with cpus set
+ *
+ * Receives a cpu list, like 1-3,5 (cpus 1, 2, 3, 5), and then set the char
+ * in the monitored_cpus.
+ *
+ * XXX: convert to a bitmask.
+ */
+int parse_cpu_list(char *cpu_list, char **monitored_cpus)
+{
+	char *mon_cpus;
+	const char *p;
+	int end_cpu;
+	int nr_cpus;
+	int cpu;
+	int i;
+
+	nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
+
+	mon_cpus = calloc(nr_cpus, sizeof(char));
+	if (!mon_cpus)
+		goto err;
+
+	for (p = cpu_list; *p; ) {
+		cpu = atoi(p);
+		if (cpu < 0 || (!cpu && *p != '0') || cpu >= nr_cpus)
+			goto err;
+
+		while (isdigit(*p))
+			p++;
+		if (*p == '-') {
+			p++;
+			end_cpu = atoi(p);
+			if (end_cpu < cpu || (!end_cpu && *p != '0') || end_cpu >= nr_cpus)
+				goto err;
+			while (isdigit(*p))
+				p++;
+		} else
+			end_cpu = cpu;
+
+		if (cpu == end_cpu) {
+			debug_msg("cpu_list: adding cpu %d\n", cpu);
+			mon_cpus[cpu] = 1;
+		} else {
+			for (i = cpu; i <= end_cpu; i++) {
+				debug_msg("cpu_list: adding cpu %d\n", i);
+				mon_cpus[i] = 1;
+			}
+		}
+
+		if (*p == ',')
+			p++;
+	}
+
+	*monitored_cpus = mon_cpus;
+
+	return 0;
+
+err:
+	debug_msg("Error parsing the cpu list %s", cpu_list);
+	return 1;
+}
+
+/*
+ * parse_duration - parse duration with s/m/h/d suffix converting it to seconds
+ */
+long parse_seconds_duration(char *val)
+{
+	char *end;
+	long t;
+
+	t = strtol(val, &end, 10);
+
+	if (end) {
+		switch (*end) {
+		case 's':
+		case 'S':
+			break;
+		case 'm':
+		case 'M':
+			t *= 60;
+			break;
+		case 'h':
+		case 'H':
+			t *= 60 * 60;
+			break;
+
+		case 'd':
+		case 'D':
+			t *= 24 * 60 * 60;
+			break;
+		}
+	}
+
+	return t;
+}
+
+/*
+ * parse_ns_duration - parse duration with ns/us/ms/s converting it to nanoseconds
+ */
+long parse_ns_duration(char *val)
+{
+	char *end;
+	long t;
+
+	t = strtol(val, &end, 10);
+
+	if (end) {
+		if (!strncmp(end, "ns", 2)) {
+			return t;
+		} else if (!strncmp(end, "us", 2)) {
+			t *= 1000;
+			return t;
+		} else if (!strncmp(end, "ms", 2)) {
+			t *= 1000 * 1000;
+			return t;
+		} else if (!strncmp(end, "s", 1)) {
+			t *= 1000 * 1000 * 1000;
+			return t;
+		}
+		return -1;
+	}
+
+	return t;
+}
+
+/*
+ * This is a set of helper functions to use SCHED_DEADLINE.
+ */
+#ifdef __x86_64__
+# define __NR_sched_setattr	314
+# define __NR_sched_getattr	315
+#elif __i386__
+# define __NR_sched_setattr	351
+# define __NR_sched_getattr	352
+#elif __arm__
+# define __NR_sched_setattr	380
+# define __NR_sched_getattr	381
+#elif __aarch64__ || __riscv
+# define __NR_sched_setattr	274
+# define __NR_sched_getattr	275
+#elif __powerpc__
+# define __NR_sched_setattr	355
+# define __NR_sched_getattr	356
+#elif __s390x__
+# define __NR_sched_setattr	345
+# define __NR_sched_getattr	346
+#endif
+
+#define SCHED_DEADLINE		6
+
+static inline int sched_setattr(pid_t pid, const struct sched_attr *attr,
+				unsigned int flags) {
+	return syscall(__NR_sched_setattr, pid, attr, flags);
+}
+
+static inline int sched_getattr(pid_t pid, struct sched_attr *attr,
+				unsigned int size, unsigned int flags)
+{
+	return syscall(__NR_sched_getattr, pid, attr, size, flags);
+}
+
+int __set_sched_attr(int pid, struct sched_attr *attr)
+{
+	int flags = 0;
+	int retval;
+
+	retval = sched_setattr(pid, attr, flags);
+	if (retval < 0) {
+		err_msg("Failed to set sched attributes to the pid %d: %s\n",
+			pid, strerror(errno));
+		return 1;
+	}
+
+	return 0;
+}
+
+/*
+ * procfs_is_workload_pid - check if a procfs entry contains a comm_prefix* comm
+ *
+ * Check if the procfs entry is a directory of a process, and then check if the
+ * process has a comm with the prefix set in char *comm_prefix. As the
+ * current users of this function only check for kernel threads, there is no
+ * need to check for the threads for the process.
+ *
+ * Return: True if the proc_entry contains a comm file with comm_prefix*.
+ * Otherwise returns false.
+ */
+static int procfs_is_workload_pid(const char *comm_prefix, struct dirent *proc_entry)
+{
+	char buffer[MAX_PATH];
+	int comm_fd, retval;
+	char *t_name;
+
+	if (proc_entry->d_type != DT_DIR)
+		return 0;
+
+	if (*proc_entry->d_name == '.')
+		return 0;
+
+	/* check if the string is a pid */
+	for (t_name = proc_entry->d_name; t_name; t_name++) {
+		if (!isdigit(*t_name))
+			break;
+	}
+
+	if (*t_name != '\0')
+		return 0;
+
+	snprintf(buffer, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
+	comm_fd = open(buffer, O_RDONLY);
+	if (comm_fd < 0)
+		return 0;
+
+	memset(buffer, 0, MAX_PATH);
+	retval = read(comm_fd, buffer, MAX_PATH);
+
+	close(comm_fd);
+
+	if (retval <= 0)
+		return 0;
+
+	retval = strncmp(comm_prefix, buffer, strlen(comm_prefix));
+	if (retval)
+		return 0;
+
+	/* comm already have \n */
+	debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, buffer);
+
+	return 1;
+}
+
+/*
+ * set_comm_sched_attr - set sched params to threads starting with char *comm_prefix
+ *
+ * This function uses procfs to list the currently running threads and then set the
+ * sched_attr *attr to the threads that start with char *comm_prefix. It is
+ * mainly used to set the priority to the kernel threads created by the
+ * tracers.
+ */
+int set_comm_sched_attr(const char *comm_prefix, struct sched_attr *attr)
+{
+	struct dirent *proc_entry;
+	DIR *procfs;
+	int retval;
+
+	if (strlen(comm_prefix) >= MAX_PATH) {
+		err_msg("Command prefix is too long: %d < strlen(%s)\n",
+			MAX_PATH, comm_prefix);
+		return 1;
+	}
+
+	procfs = opendir("/proc");
+	if (!procfs) {
+		err_msg("Could not open procfs\n");
+		return 1;
+	}
+
+	while ((proc_entry = readdir(procfs))) {
+
+		retval = procfs_is_workload_pid(comm_prefix, proc_entry);
+		if (!retval)
+			continue;
+
+		/* procfs_is_workload_pid confirmed it is a pid */
+		retval = __set_sched_attr(atoi(proc_entry->d_name), attr);
+		if (retval) {
+			err_msg("Error setting sched attributes for pid:%s\n", proc_entry->d_name);
+			goto out_err;
+		}
+
+		debug_msg("Set sched attributes for pid:%s\n", proc_entry->d_name);
+	}
+	return 0;
+
+out_err:
+	closedir(procfs);
+	return 1;
+}
+
+#define INVALID_VAL	(~0L)
+static long get_long_ns_after_colon(char *start)
+{
+	long val = INVALID_VAL;
+
+	/* find the ":" */
+	start = strstr(start, ":");
+	if (!start)
+		return -1;
+
+	/* skip ":" */
+	start++;
+	val = parse_ns_duration(start);
+
+	return val;
+}
+
+static long get_long_after_colon(char *start)
+{
+	long val = INVALID_VAL;
+
+	/* find the ":" */
+	start = strstr(start, ":");
+	if (!start)
+		return -1;
+
+	/* skip ":" */
+	start++;
+	val = get_llong_from_str(start);
+
+	return val;
+}
+
+/*
+ * parse priority in the format:
+ * SCHED_OTHER:
+ *		o:<prio>
+ *		O:<prio>
+ * SCHED_RR:
+ *		r:<prio>
+ *		R:<prio>
+ * SCHED_FIFO:
+ *		f:<prio>
+ *		F:<prio>
+ * SCHED_DEADLINE:
+ *		d:runtime:period
+ *		D:runtime:period
+ */
+int parse_prio(char *arg, struct sched_attr *sched_param)
+{
+	long prio;
+	long runtime;
+	long period;
+
+	memset(sched_param, 0, sizeof(*sched_param));
+	sched_param->size = sizeof(*sched_param);
+
+	switch (arg[0]) {
+	case 'd':
+	case 'D':
+		/* d:runtime:period */
+		if (strlen(arg) < 4)
+			return -1;
+
+		runtime = get_long_ns_after_colon(arg);
+		if (runtime == INVALID_VAL)
+			return -1;
+
+		period = get_long_ns_after_colon(&arg[2]);
+		if (period == INVALID_VAL)
+			return -1;
+
+		if (runtime > period)
+			return -1;
+
+		sched_param->sched_policy   = SCHED_DEADLINE;
+		sched_param->sched_runtime  = runtime;
+		sched_param->sched_deadline = period;
+		sched_param->sched_period   = period;
+		break;
+	case 'f':
+	case 'F':
+		/* f:prio */
+		prio = get_long_after_colon(arg);
+		if (prio == INVALID_VAL)
+			return -1;
+
+		if (prio < sched_get_priority_min(SCHED_FIFO))
+			return -1;
+		if (prio > sched_get_priority_max(SCHED_FIFO))
+			return -1;
+
+		sched_param->sched_policy   = SCHED_FIFO;
+		sched_param->sched_priority = prio;
+		break;
+	case 'r':
+	case 'R':
+		/* r:prio */
+		prio = get_long_after_colon(arg);
+		if (prio == INVALID_VAL)
+			return -1;
+
+		if (prio < sched_get_priority_min(SCHED_RR))
+			return -1;
+		if (prio > sched_get_priority_max(SCHED_RR))
+			return -1;
+
+		sched_param->sched_policy   = SCHED_RR;
+		sched_param->sched_priority = prio;
+		break;
+	case 'o':
+	case 'O':
+		/* o:prio */
+		prio = get_long_after_colon(arg);
+		if (prio == INVALID_VAL)
+			return -1;
+
+		if (prio < sched_get_priority_min(SCHED_OTHER))
+			return -1;
+		if (prio > sched_get_priority_max(SCHED_OTHER))
+			return -1;
+
+		sched_param->sched_policy   = SCHED_OTHER;
+		sched_param->sched_priority = prio;
+		break;
+	default:
+		return -1;
+	}
+	return 0;
+}
+
+/*
+ * set_cpu_dma_latency - set the /dev/cpu_dma_latecy
+ *
+ * This is used to reduce the exit from idle latency. The value
+ * will be reset once the file descriptor of /dev/cpu_dma_latecy
+ * is closed.
+ *
+ * Return: the /dev/cpu_dma_latecy file descriptor
+ */
+int set_cpu_dma_latency(int32_t latency)
+{
+	int retval;
+	int fd;
+
+	fd = open("/dev/cpu_dma_latency", O_RDWR);
+	if (fd < 0) {
+		err_msg("Error opening /dev/cpu_dma_latency\n");
+		return -1;
+	}
+
+	retval = write(fd, &latency, 4);
+	if (retval < 1) {
+		err_msg("Error setting /dev/cpu_dma_latency\n");
+		close(fd);
+		return -1;
+	}
+
+	debug_msg("Set /dev/cpu_dma_latency to %d\n", latency);
+
+	return fd;
+}