WireGuard Linux

https://github.com/wireguard/wireguard-linux
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### Boot setup command example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scsi/sym53c8xx_2.rst

Example of a boot setup command under lilo prompt, enabling tagged commands, setting synchronous negotiation speed, and setting DEBUG_NEGO flag.

```text
lilo: linux root=/dev/sda2 sym53c8xx.cmd_per_lun=4 sym53c8xx.sync=10 sym53c8xx.debug=0x200
```

--------------------------------

### modprobe command example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scsi/sym53c8xx_2.rst

Installs the driver module with the same options as the boot setup command.

```text
modprobe sym53c8xx cmd_per_lun=4 sync=10 debug=0x200
```

--------------------------------

### LILO boot setup command example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scsi/ncr53c8xx.rst

Example of passing configuration options to the ncr53c8xx driver at the LILO boot prompt.

```text
lilo: linux root=/dev/hda2 ncr53c8xx=tags:4,sync:10,debug:0x200
```

--------------------------------

### Personal system boot setup command

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scsi/ncr53c8xx.rst

An example of a specific, functional boot setup command used on a personal system.

```text
ncr53c8xx=mpar:y,spar:y,disc:y,specf:1,fsn:n,ultra:2,fsn:n,revprob:n,verb:1\
          tags:32,sync:12,debug:0,burst:7,led:1,wide:1,settle:2,diff:0,irqm:0
```

--------------------------------

### Board setup code implementation

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/arch/sh/new-machine.rst

Example implementation of get_system_type() and platform_setup() for a new board.

```c
/*
* arch/sh/boards/vapor/setup.c - Setup code for imaginary board
*/
#include <linux/init.h>

const char *get_system_type(void)
{
	    return "FooTech Vaporboard";
}

int __init platform_setup(void)
{
	    /*
	    * If our hardware actually existed, we would do real
	    * setup here. Though it's also sane to leave this empty
	    * if there's no real init work that has to be done for
	    * this board.
	    */

	    /* Start-up imaginary PCI ... */

	    /* And whatever else ... */

	    return 0;
}
```

--------------------------------

### KVM_PPC_RESIZE_HPT_PREPARE

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/virt/kvm/api.rst

Starts, stops, or monitors the preparation of a new Hashed Page Table (HPT) for the guest, implementing the H_RESIZE_HPT_PREPARE hypercall. This ioctl is used for runtime resizing of the guest's HPT.

```APIDOC
## KVM_PPC_RESIZE_HPT_PREPARE

### Description
Starts, stops, or monitors the preparation of a new Hashed Page Table (HPT) for the guest, implementing the H_RESIZE_HPT_PREPARE hypercall. This ioctl is used for runtime resizing of the guest's HPT.

### Capability
KVM_CAP_SPAPR_RESIZE_HPT

### Architectures
powerpc

### Type
vm ioctl

### Parameters
struct kvm_ppc_resize_hpt (in)

### Returns
0 on successful completion, >0 if a new HPT is being prepared (estimated milliseconds until completion), -EFAULT if struct kvm_reinject_control cannot be read, -EINVAL if the supplied shift or flags are invalid, -ENOMEM if unable to allocate the new HPT.

### Request Structure
struct kvm_ppc_resize_hpt {
    __u64 flags;
    __u32 shift;
    __u32 pad;
};

### Parameters Description
- **flags** (__u64) - Required - Flags for the operation.
- **shift** (__u32) - Required - If >0 and no pending HPT, begins preparation of a new HPT of size 2^shift bytes.
- **pad** (__u32) - Reserved - Must be zero.

### Notes
If called with shift > 0 and no pending HPT, it begins preparation and returns a positive integer with estimated milliseconds until completion.
```

--------------------------------

### KVM_S390_GET_SKEYS

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/virt/kvm/api.rst

Gets guest storage key values on s390 architecture. Takes parameters via struct kvm_s390_skeys.

```APIDOC
## KVM_S390_GET_SKEYS

### Description
Gets guest storage key values on s390 architecture. Takes parameters via struct kvm_s390_skeys.

### Capability
KVM_CAP_S390_SKEYS

### Architectures
s390

### Type
vm ioctl

### Parameters
struct kvm_s390_skeys

### Returns
0 on success, KVM_S390_GET_SKEYS_NONE if guest is not using storage keys, negative value on error

### Struct Definition
struct kvm_s390_skeys {
    __u64 start_gfn;
    __u64 count;
    __u64 skeydata_addr;
    __u32 flags;
    __u32 reserved[9];
};

### Parameters
- start_gfn (__u64) - Required - Number of the first guest frame whose storage keys to get.
- count (__u64) - Required - Number of consecutive frames (starting from start_gfn) whose storage keys to get. Must be at least 1 and maximum allowed value is KVM_S390_SKEYS_MAX. Values outside this range cause -EINVAL.
- skeydata_addr (__u64) - Required - Address to a buffer large enough to hold count bytes. This buffer will be filled with storage key data by the ioctl.

```

--------------------------------

### Example setup_data and setup_indirect usage

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/arch/x86/boot.rst

An example demonstrating how to point to SETUP_E820_EXT data using the setup_indirect structure.

```c
struct setup_data {
	.next = 0,	/* or <addr_of_next_setup_data_struct> */
	.type = SETUP_INDIRECT,
	.len = sizeof(setup_indirect),
	.data[sizeof(setup_indirect)] = (struct setup_indirect) {
		.type = SETUP_INDIRECT | SETUP_E820_EXT,
		.reserved = 0,
		.len = <len_of_SETUP_E820_EXT_data>,
		.addr = <addr_of_SETUP_E820_EXT_data>,
	},
   }
```

--------------------------------

### Setup and teardown a statically allocated state

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/core-api/cpu_hotplug.rst

Example of setting up and removing a statically allocated state in the STARTING section for online and offline notifications.

```c
ret = cpuhp_setup_state(CPUHP_SUBSYS_STARTING, "subsys:starting", subsys_cpu_starting, subsys_cpu_dying);
   if (ret < 0)
        return ret;
   ....
   cpuhp_remove_state(CPUHP_SUBSYS_STARTING);
```

--------------------------------

### ionice start process example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/block/ioprio.rst

Example of starting a process with specific io priority settings.

```bash
# ionice -c2 -n0 /bin/ls
```

--------------------------------

### Initialize two lists for list_splice()

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/core-api/list.rst

Starts a function that will splice two lists together using list_splice(). It initializes two list heads, knie and stey, with LIST_HEAD_INIT(). The example is incomplete in the source, showing only the setup portion.

```c
static void circus_clowns_splice(void)
{
        struct clown *grock, *dimitri, *pic, *alfredo, *pio;
        struct list_head knie = LIST_HEAD_INIT(knie);
        struct list_head stey = LIST_HEAD_INIT(stey);
```

--------------------------------

### Bootconfig Syntax Example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/bootconfig.rst

Demonstrates the basic key-value syntax, including comments and multi-line list elements.

```text
 # comment line
 foo = value # value is set to foo.
 bar = 1, # 1st element
       2, # 2nd element
       3  # 3rd element
```

--------------------------------

### Start manually installed Espeakup

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/spkguide.txt

Execute the Espeakup binary directly if it was installed manually.

```bash
/usr/bin/espeakup
```

--------------------------------

### Create example.c source file

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/dev-tools/kunit/start.rst

Implement the function to be tested.

```c
#include <linux/errno.h>

#include "example.h"

int misc_example_add(int left, int right)
{
	return left + right;
}
```

--------------------------------

### Install stress-ng and paxtest

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/workload-tracing.rst

Install stress-ng and paxtest, which are used as example workloads for tracing.

```bash
apt-get install stress-ng
apt-get install paxtest
```

--------------------------------

### Example bootconfig file structure

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/bootconfig.rst

A sample configuration file defining kernel and init parameters.

```text
kernel {
   root = 01234567-89ab-cdef-0123-456789abcd
 }
 init {
  splash
 }
```

--------------------------------

### Iterate over LPM trie map entries in C

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/bpf/map_lpm_trie.rst

Iterates through all entries of an LPM trie map using bpf_map_get_next_key and bpf_map_lookup_elem. The loop starts with a NULL key to get the first entry and continues until bpf_map_get_next_key returns an error. The example includes placeholder comments for using the key and value.

```c
#include <bpf/libbpf.h>
#include <bpf/bpf.h>

void iterate_lpm_trie(int map_fd)
{
        struct ipv4_lpm_key *cur_key = NULL;
        struct ipv4_lpm_key next_key;
        struct value value;
        int err;

        for (;;) {
                err = bpf_map_get_next_key(map_fd, cur_key, &next_key);
                if (err)
                        break;

                bpf_map_lookup_elem(map_fd, &next_key, &value);

                /* Use key and value here */

                cur_key = &next_key;
        }
}
```

--------------------------------

### USB Monitor Input Control Transfer Example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/usb/usbmon.rst

Example of an input control transfer to get a port status.

```text
d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
```

--------------------------------

### Building and Running the Simple Scheduler

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scheduler/sched-ext.rst

Commands to build the example schedulers and execute the simple scheduler.

```none
# make -j16 -C tools/sched_ext
# tools/sched_ext/build/bin/scx_simple
local=0 global=3
local=5 global=24
local=9 global=44
local=13 global=56
local=17 global=72
^CEXIT: BPF scheduler unregistered
```

--------------------------------

### Implement platform setup callback

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/fb/ep93xx-fb.rst

Access the platform data and driver data within the board-specific setup callback.

```c
static int some_board_fb_setup(struct platform_device *pdev)
{
	struct ep93xxfb_mach_info *mach_info = pdev->dev.platform_data;
	struct fb_info *fb_info = platform_get_drvdata(pdev);

	/* Board specific framebuffer setup */
}
```

--------------------------------

### Safe boot setup commands

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/scsi/ncr53c8xx.rst

Alternative boot setup commands for installation diskettes or systems requiring a safe configuration.

```text
ncr53c8xx=safe:y,mpar:y,disc:y
ncr53c8xx=safe:y,disc:y
ncr53c8xx=safe:y,mpar:y
ncr53c8xx=safe:y
```

--------------------------------

### Driver Load Examples

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/networking/device_drivers/ethernet/dlink/dl2k.rst

Examples of loading the driver with specific media parameters.

```bash
insmod dl2k.o media=100mbps_hd
```

```bash
insmod dl2k.o media=3
```

```bash
insmod dl2k.o media=3,2	; for 2 cards
```

--------------------------------

### Quick Install Commands

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/networking/device_drivers/ethernet/dlink/dl2k.rst

Commands to compile, load, and configure the driver for immediate use.

```bash
1. make all
2. insmod dl2k.ko
3. ifconfig eth0 up 10.xxx.xxx.xxx netmask 255.0.0.0
			^^^^^^^^^^^^^^^\	    ^^^^^^^^
					IP		     NETMASK
```

```bash
4. cp dl2k.ko /lib/modules/`uname -r`/kernel/drivers/net
```

```bash
alias eth0 dl2k
```

```bash
6. Run depmod to updated module indexes.
7. Run netconfig or netconf to create configuration script ifcfg-eth0
   located at /etc/sysconfig/network-scripts or create it manually.

   [see - Configuration Script Sample]
8. Driver will automatically load and configure at next boot time.
```

--------------------------------

### Get fd with get_unused_fd_flags

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/driver-api/sync_file.rst

Gets an unused file descriptor with the O_CLOEXEC flag, which is needed to install the sync_file's file into the fd table.

```c
fd = get_unused_fd_flags(O_CLOEXEC);
```

--------------------------------

### Linear array boot example

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/device-mapper/dm-init.rst

Example of booting to a linear array made up of user-mode linux block devices.

```text
dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" root=/dev/dm-0
```

--------------------------------

### Get number of performance profiles

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/pm/intel-speed-select.rst

Command to get the number of performance profiles, with example output showing 4 profiles on the test system.

```bash
 # intel-speed-select perf-profile get-config-levels
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
        get-config-levels:4
 package-1
  die-0
    cpu-14
        get-config-levels:4
```

--------------------------------

### Setup steps for a new cgroup job

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/admin-guide/cgroup-v1/cgroups.rst

General procedure for mounting the cgroup filesystem, creating a cgroup, and attaching a task to it.

```bash
 1) mount -t tmpfs cgroup_root /sys/fs/cgroup
 2) mkdir /sys/fs/cgroup/cpuset
 3) mount -t cgroup -ocpuset cpuset /sys/fs/cgroup/cpuset
 4) Create the new cgroup by doing mkdir's and write's (or echo's) in
    the /sys/fs/cgroup/cpuset virtual file system.
 5) Start a task that will be the "founding father" of the new job.
 6) Attach that task to the new cgroup by writing its PID to the
    /sys/fs/cgroup/cpuset tasks file for that cgroup.
 7) fork, exec or clone the job tasks from this founding father task.
```

--------------------------------

### Get delays for a specific pid

Source: https://github.com/wireguard/wireguard-linux/blob/stable/Documentation/accounting/delay-accounting.rst

Example command to get delays since system boot for pid 10. The output is similar to the next case.

```text
# ./getdelays -d -p 10
```
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