Merge tag 'trace-v5.6-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

In both styles, same key words are automatically merged when parsing it

at boot time. So you can append similar trees or key-values.

Same-key Values

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

It is prohibited that two or more values or arrays share a same-key.

For example,::

 foo = bar, baz

 foo = qux  # !ERROR! we can not re-define same key

If you want to append the value to existing key as an array member,

you can use ``+=`` operator. For example::

 foo = bar, baz

 foo += qux

In this case, the key ``foo`` has ``bar``, ``baz`` and ``qux``.

However, a sub-key and a value can not co-exist under a parent key.

For example, following config is NOT allowed.::

 foo = value1

 foo.bar = value2 # !ERROR! subkey "bar" and value "value1" can NOT co-exist

Comments

--------

==============================

Since the boot configuration file is loaded with initrd, it will be added

to the end of the initrd (initramfs) image file. The Linux kernel decodes

the last part of the initrd image in memory to get the boot configuration

data.

to the end of the initrd (initramfs) image file with size, checksum and

12-byte magic word as below.

[initrd][bootconfig][size(u32)][checksum(u32)][#BOOTCONFIG\n]

The Linux kernel decodes the last part of the initrd image in memory to

get the boot configuration data.

Because of this "piggyback" method, there is no need to change or

update the boot loader and the kernel image itself.

#include <linux/kernel.h>

#include <linux/types.h>

#define BOOTCONFIG_MAGIC	"#BOOTCONFIG\n"

#define BOOTCONFIG_MAGIC_LEN	12

/* XBC tree node */

struct xbc_node {

	u16 next;

config BOOT_CONFIG

	bool "Boot config support"

	depends on BLK_DEV_INITRD

	default y

	select BLK_DEV_INITRD

	help

	  Extra boot config allows system admin to pass a config file as

	  complemental extension of kernel cmdline when booting.

	  The boot config file must be attached at the end of initramfs

	  with checksum and size.

	  with checksum, size and magic word.

	  See <file:Documentation/admin-guide/bootconfig.rst> for details.

	  If unsure, say Y.

{

	struct xbc_node *knode, *vnode;

	char *end = buf + size;

	char c = '\"';

	const char *val;

	int ret;

			return ret;

		vnode = xbc_node_get_child(knode);

		ret = snprintf(buf, rest(buf, end), "%s%c", xbc_namebuf,

				vnode ? '=' : ' ');

		if (!vnode) {

			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);

			if (ret < 0)

				return ret;

			buf += ret;

		if (!vnode)

			continue;

		c = '\"';

		}

		xbc_array_for_each_value(vnode, val) {

			ret = snprintf(buf, rest(buf, end), "%c%s", c, val);

			ret = snprintf(buf, rest(buf, end), "%s=\"%s\" ",

				       xbc_namebuf, val);

			if (ret < 0)

				return ret;

			buf += ret;

			c = ',';

		}

		if (rest(buf, end) > 2)

			strcpy(buf, "\" ");

		buf += 2;

	}

	return buf - (end - size);

	return new_cmdline;

}

u32 boot_config_checksum(unsigned char *p, u32 size)

static u32 boot_config_checksum(unsigned char *p, u32 size)

{

	u32 ret = 0;

	if (!initrd_end)

		goto not_found;

	hdr = (u32 *)(initrd_end - 8);

	data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN;

	if (memcmp(data, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN))

		goto not_found;

	hdr = (u32 *)(data - 8);

	size = hdr[0];

	csum = hdr[1];

}

#else

#define setup_boot_config(cmdline)	do { } while (0)

static int __init warn_bootconfig(char *str)

{

	pr_warn("WARNING: 'bootconfig' found on the kernel command line but CONFIG_BOOTCONFIG is not set.\n");

	return 0;

}

early_param("bootconfig", warn_bootconfig);

#endif

/* Change NUL term back to "=", to make "param" the whole string. */

config BOOTTIME_TRACING

	bool "Boot-time Tracing support"

	depends on BOOT_CONFIG && TRACING

	default y

	depends on TRACING

	select BOOT_CONFIG

	help

	  Enable developer to setup ftrace subsystem via supplemental

	  kernel cmdline at boot time for debugging (tracing) driver