lib/seq_buf.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * seq_buf.c
  *
  * Copyright (C) 2014 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
  *
  * The seq_buf is a handy tool that allows you to pass a descriptor around
  * to a buffer that other functions can write to. It is similar to the
  * seq_file functionality but has some differences.
  *
  * To use it, the seq_buf must be initialized with seq_buf_init().
  * This will set up the counters within the descriptor. You can call
  * seq_buf_init() more than once to reset the seq_buf to start
  * from scratch.
  */

 #include <linux/bug.h>
 #include <linux/err.h>
 #include <linux/export.h>
 #include <linux/hex.h>
 #include <linux/minmax.h>
 #include <linux/printk.h>
 #include <linux/seq_buf.h>
 #include <linux/seq_file.h>
 #include <linux/sprintf.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>

 /**
  * seq_buf_can_fit - can the new data fit in the current buffer?
  * @s: the seq_buf descriptor
  * @len: The length to see if it can fit in the current buffer
  *
  * Returns: true if there's enough unused space in the seq_buf buffer
  * to fit the amount of new data according to @len.
  */
 static bool seq_buf_can_fit(struct seq_buf *s, size_t len)
 {
 	return s->len + len <= s->size;
 }

 /**
  * seq_buf_print_seq - move the contents of seq_buf into a seq_file
  * @m: the seq_file descriptor that is the destination
  * @s: the seq_buf descriptor that is the source.
  *
  * Returns: zero on success, non-zero otherwise.
  */
 int seq_buf_print_seq(struct seq_file *m, struct seq_buf *s)
 {
 	unsigned int len = seq_buf_used(s);

 	return seq_write(m, s->buffer, len);
 }

 /**
  * seq_buf_vprintf - sequence printing of information.
  * @s: seq_buf descriptor
  * @fmt: printf format string
  * @args: va_list of arguments from a printf() type function
  *
  * Writes a vnprintf() format into the sequence buffer.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args)
 {
 	int len;

 	WARN_ON(s->size == 0);

 	if (s->len < s->size) {
 		len = vsnprintf(s->buffer + s->len, s->size - s->len, fmt, args);
 		if (s->len + len < s->size) {
 			s->len += len;
 			return 0;
 		}
 	}
 	seq_buf_set_overflow(s);
 	return -1;
 }

 /**
  * seq_buf_printf - sequence printing of information
  * @s: seq_buf descriptor
  * @fmt: printf format string
  *
  * Writes a printf() format into the sequence buffer.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...)
 {
 	va_list ap;
 	int ret;

 	va_start(ap, fmt);
 	ret = seq_buf_vprintf(s, fmt, ap);
 	va_end(ap);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(seq_buf_printf);

 /**
  * seq_buf_do_printk - printk() seq_buf line by line
  * @s: seq_buf descriptor
  * @lvl: printk level
  *
  * printk()-s a multi-line sequential buffer line by line. The function
  * makes sure that the buffer in @s is NUL-terminated and safe to read
  * as a string.
  */
 void seq_buf_do_printk(struct seq_buf *s, const char *lvl)
 {
 	const char *start, *lf;

 	if (s->size == 0 || s->len == 0)
 		return;

 	start = seq_buf_str(s);
 	while ((lf = strchr(start, '\n'))) {
 		int len = lf - start + 1;

 		printk("%s%.*s", lvl, len, start);
 		start = ++lf;
 	}

 	/* No trailing LF */
 	if (start < s->buffer + s->len)
 		printk("%s%s\n", lvl, start);
 }
 EXPORT_SYMBOL_GPL(seq_buf_do_printk);

 #ifdef CONFIG_BINARY_PRINTF
 /**
  * seq_buf_bprintf - Write the printf string from binary arguments
  * @s: seq_buf descriptor
  * @fmt: The format string for the @binary arguments
  * @binary: The binary arguments for @fmt.
  *
  * When recording in a fast path, a printf may be recorded with just
  * saving the format and the arguments as they were passed to the
  * function, instead of wasting cycles converting the arguments into
  * ASCII characters. Instead, the arguments are saved in a 32 bit
  * word array that is defined by the format string constraints.
  *
  * This function will take the format and the binary array and finish
  * the conversion into the ASCII string within the buffer.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary)
 {
 	unsigned int len = seq_buf_buffer_left(s);
 	int ret;

 	WARN_ON(s->size == 0);

 	if (s->len < s->size) {
 		ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
 		if (s->len + ret < s->size) {
 			s->len += ret;
 			return 0;
 		}
 	}
 	seq_buf_set_overflow(s);
 	return -1;
 }
 #endif /* CONFIG_BINARY_PRINTF */

 /**
  * seq_buf_puts - sequence printing of simple string
  * @s: seq_buf descriptor
  * @str: simple string to record
  *
  * Copy a simple string into the sequence buffer.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_puts(struct seq_buf *s, const char *str)
 {
 	size_t len = strlen(str);

 	WARN_ON(s->size == 0);

 	/* Add 1 to len for the trailing null byte which must be there */
 	len += 1;

 	if (seq_buf_can_fit(s, len)) {
 		memcpy(s->buffer + s->len, str, len);
 		/* Don't count the trailing null byte against the capacity */
 		s->len += len - 1;
 		return 0;
 	}
 	seq_buf_set_overflow(s);
 	return -1;
 }
 EXPORT_SYMBOL_GPL(seq_buf_puts);

 /**
  * seq_buf_putc - sequence printing of simple character
  * @s: seq_buf descriptor
  * @c: simple character to record
  *
  * Copy a single character into the sequence buffer.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_putc(struct seq_buf *s, unsigned char c)
 {
 	WARN_ON(s->size == 0);

 	if (seq_buf_can_fit(s, 1)) {
 		s->buffer[s->len++] = c;
 		return 0;
 	}
 	seq_buf_set_overflow(s);
 	return -1;
 }
 EXPORT_SYMBOL_GPL(seq_buf_putc);

 /**
  * seq_buf_putmem - write raw data into the sequence buffer
  * @s: seq_buf descriptor
  * @mem: The raw memory to copy into the buffer
  * @len: The length of the raw memory to copy (in bytes)
  *
  * There may be cases where raw memory needs to be written into the
  * buffer and a strcpy() would not work. Using this function allows
  * for such cases.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len)
 {
 	WARN_ON(s->size == 0);

 	if (seq_buf_can_fit(s, len)) {
 		memcpy(s->buffer + s->len, mem, len);
 		s->len += len;
 		return 0;
 	}
 	seq_buf_set_overflow(s);
 	return -1;
 }

 #define MAX_MEMHEX_BYTES	8U
 #define HEX_CHARS		(MAX_MEMHEX_BYTES*2 + 1)

 /**
  * seq_buf_putmem_hex - write raw memory into the buffer in ASCII hex
  * @s: seq_buf descriptor
  * @mem: The raw memory to write its hex ASCII representation of
  * @len: The length of the raw memory to copy (in bytes)
  *
  * This is similar to seq_buf_putmem() except instead of just copying the
  * raw memory into the buffer it writes its ASCII representation of it
  * in hex characters.
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
 		       unsigned int len)
 {
 	unsigned char hex[HEX_CHARS];
 	const unsigned char *data = mem;
 	unsigned int start_len;
 	int i, j;

 	WARN_ON(s->size == 0);

 	BUILD_BUG_ON(MAX_MEMHEX_BYTES * 2 >= HEX_CHARS);

 	while (len) {
 		start_len = min(len, MAX_MEMHEX_BYTES);
 #ifdef __BIG_ENDIAN
 		for (i = 0, j = 0; i < start_len; i++) {
 #else
 		for (i = start_len-1, j = 0; i >= 0; i--) {
 #endif
 			hex[j++] = hex_asc_hi(data[i]);
 			hex[j++] = hex_asc_lo(data[i]);
 		}
 		if (WARN_ON_ONCE(j == 0 || j/2 > len))
 			break;

 		/* j increments twice per loop */
 		hex[j++] = ' ';

 		seq_buf_putmem(s, hex, j);
 		if (seq_buf_has_overflowed(s))
 			return -1;

 		len -= start_len;
 		data += start_len;
 	}
 	return 0;
 }

 /**
  * seq_buf_path - copy a path into the sequence buffer
  * @s: seq_buf descriptor
  * @path: path to write into the sequence buffer.
  * @esc: set of characters to escape in the output
  *
  * Write a path name into the sequence buffer.
  *
  * Returns: the number of written bytes on success, -1 on overflow.
  */
 int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 {
 	char *buf;
 	size_t size = seq_buf_get_buf(s, &buf);
 	int res = -1;

 	WARN_ON(s->size == 0);

 	if (size) {
 		char *p = d_path(path, buf, size);
 		if (!IS_ERR(p)) {
 			char *end = mangle_path(buf, p, esc);
 			if (end)
 				res = end - buf;
 		}
 	}
 	seq_buf_commit(s, res);

 	return res;
 }

 /**
  * seq_buf_to_user - copy the sequence buffer to user space
  * @s: seq_buf descriptor
  * @ubuf: The userspace memory location to copy to
  * @start: The first byte in the buffer to copy
  * @cnt: The amount to copy
  *
  * Copies the sequence buffer into the userspace memory pointed to
  * by @ubuf. It starts from @start and writes up to @cnt characters
  * or until it reaches the end of the content in the buffer (@s->len),
  * whichever comes first.
  *
  * Returns:
  * On success, it returns a positive number of the number of bytes
  * it copied.
  *
  * On failure it returns -EBUSY if all of the content in the
  * sequence has been already read, which includes nothing in the
  * sequence (@s->len == @start).
  *
  * Returns -EFAULT if the copy to userspace fails.
  */
 int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, size_t start, int cnt)
 {
 	int len;
 	int ret;

 	if (!cnt)
 		return 0;

 	len = seq_buf_used(s);

 	if (len <= start)
 		return -EBUSY;

 	len -= start;
 	if (cnt > len)
 		cnt = len;
 	ret = copy_to_user(ubuf, s->buffer + start, cnt);
 	if (ret == cnt)
 		return -EFAULT;

 	return cnt - ret;
 }

 /**
  * seq_buf_hex_dump - print formatted hex dump into the sequence buffer
  * @s: seq_buf descriptor
  * @prefix_str: string to prefix each line with;
  *  caller supplies trailing spaces for alignment if desired
  * @prefix_type: controls whether prefix of an offset, address, or none
  *  is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
  * @rowsize: number of bytes to print per line; must be 16 or 32
  * @groupsize: number of bytes to print at a time (1, 2, 4, 8; default = 1)
  * @buf: data blob to dump
  * @len: number of bytes in the @buf
  * @ascii: include ASCII after the hex output
  *
  * Function is an analogue of print_hex_dump() and thus has similar interface.
  *
  * linebuf size is maximal length for one line.
  * 32 * 3 - maximum bytes per line, each printed into 2 chars + 1 for
  *	separating space
  * 2 - spaces separating hex dump and ASCII representation
  * 32 - ASCII representation
  * 1 - terminating '\0'
  *
  * Returns: zero on success, -1 on overflow.
  */
 int seq_buf_hex_dump(struct seq_buf *s, const char *prefix_str, int prefix_type,
 		     int rowsize, int groupsize,
 		     const void *buf, size_t len, bool ascii)
 {
 	const u8 *ptr = buf;
 	int i, linelen, remaining = len;
 	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
 	int ret;

 	if (rowsize != 16 && rowsize != 32)
 		rowsize = 16;

 	for (i = 0; i < len; i += rowsize) {
 		linelen = min(remaining, rowsize);
 		remaining -= rowsize;

 		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
 				   linebuf, sizeof(linebuf), ascii);

 		switch (prefix_type) {
 		case DUMP_PREFIX_ADDRESS:
 			ret = seq_buf_printf(s, "%s%p: %s\n",
 			       prefix_str, ptr + i, linebuf);
 			break;
 		case DUMP_PREFIX_OFFSET:
 			ret = seq_buf_printf(s, "%s%.8x: %s\n",
 					     prefix_str, i, linebuf);
 			break;
 		default:
 			ret = seq_buf_printf(s, "%s%s\n", prefix_str, linebuf);
 			break;
 		}
 		if (ret)
 			return ret;
 	}
 	return 0;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* seq_buf.c
	*
	* Copyright (C) 2014 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
	*
	* The seq_buf is a handy tool that allows you to pass a descriptor around
	* to a buffer that other functions can write to. It is similar to the
	* seq_file functionality but has some differences.
	*
	* To use it, the seq_buf must be initialized with seq_buf_init().
	* This will set up the counters within the descriptor. You can call
	* seq_buf_init() more than once to reset the seq_buf to start
	* from scratch.
	*/

	#include <linux/bug.h>
	#include <linux/err.h>
	#include <linux/export.h>
	#include <linux/hex.h>
	#include <linux/minmax.h>
	#include <linux/printk.h>
	#include <linux/seq_buf.h>
	#include <linux/seq_file.h>
	#include <linux/sprintf.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/uaccess.h>

	/**
	* seq_buf_can_fit - can the new data fit in the current buffer?
	* @s: the seq_buf descriptor
	* @len: The length to see if it can fit in the current buffer
	*
	* Returns: true if there's enough unused space in the seq_buf buffer
	* to fit the amount of new data according to @len.
	*/
	static bool seq_buf_can_fit(struct seq_buf *s, size_t len)
	{
	return s->len + len <= s->size;
	}

	/**
	* seq_buf_print_seq - move the contents of seq_buf into a seq_file
	* @m: the seq_file descriptor that is the destination
	* @s: the seq_buf descriptor that is the source.
	*
	* Returns: zero on success, non-zero otherwise.
	*/
	int seq_buf_print_seq(struct seq_file m, struct seq_buf s)
	{
	unsigned int len = seq_buf_used(s);

	return seq_write(m, s->buffer, len);
	}

	/**
	* seq_buf_vprintf - sequence printing of information.
	* @s: seq_buf descriptor
	* @fmt: printf format string
	* @args: va_list of arguments from a printf() type function
	*
	* Writes a vnprintf() format into the sequence buffer.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_vprintf(struct seq_buf s, const char fmt, va_list args)
	{
	int len;

	WARN_ON(s->size == 0);

	if (s->len < s->size) {
	len = vsnprintf(s->buffer + s->len, s->size - s->len, fmt, args);
	if (s->len + len < s->size) {
	s->len += len;
	return 0;
	}
	}
	seq_buf_set_overflow(s);
	return -1;
	}

	/**
	* seq_buf_printf - sequence printing of information
	* @s: seq_buf descriptor
	* @fmt: printf format string
	*
	* Writes a printf() format into the sequence buffer.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_printf(struct seq_buf s, const char fmt, ...)
	{
	va_list ap;
	int ret;

	va_start(ap, fmt);
	ret = seq_buf_vprintf(s, fmt, ap);
	va_end(ap);

	return ret;
	}
	EXPORT_SYMBOL_GPL(seq_buf_printf);

	/**
	* seq_buf_do_printk - printk() seq_buf line by line
	* @s: seq_buf descriptor
	* @lvl: printk level
	*
	* printk()-s a multi-line sequential buffer line by line. The function
	* makes sure that the buffer in @s is NUL-terminated and safe to read
	* as a string.
	*/
	void seq_buf_do_printk(struct seq_buf s, const char lvl)
	{
	const char start, lf;

	if (s->size == 0 \|\| s->len == 0)
	return;

	start = seq_buf_str(s);
	while ((lf = strchr(start, '\n'))) {
	int len = lf - start + 1;

	printk("%s%.*s", lvl, len, start);
	start = ++lf;
	}

	/* No trailing LF */
	if (start < s->buffer + s->len)
	printk("%s%s\n", lvl, start);
	}
	EXPORT_SYMBOL_GPL(seq_buf_do_printk);

	#ifdef CONFIG_BINARY_PRINTF
	/**
	* seq_buf_bprintf - Write the printf string from binary arguments
	* @s: seq_buf descriptor
	* @fmt: The format string for the @binary arguments
	* @binary: The binary arguments for @fmt.
	*
	* When recording in a fast path, a printf may be recorded with just
	* saving the format and the arguments as they were passed to the
	* function, instead of wasting cycles converting the arguments into
	* ASCII characters. Instead, the arguments are saved in a 32 bit
	* word array that is defined by the format string constraints.
	*
	* This function will take the format and the binary array and finish
	* the conversion into the ASCII string within the buffer.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_bprintf(struct seq_buf s, const char fmt, const u32 *binary)
	{
	unsigned int len = seq_buf_buffer_left(s);
	int ret;

	WARN_ON(s->size == 0);

	if (s->len < s->size) {
	ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
	if (s->len + ret < s->size) {
	s->len += ret;
	return 0;
	}
	}
	seq_buf_set_overflow(s);
	return -1;
	}
	#endif /* CONFIG_BINARY_PRINTF */

	/**
	* seq_buf_puts - sequence printing of simple string
	* @s: seq_buf descriptor
	* @str: simple string to record
	*
	* Copy a simple string into the sequence buffer.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_puts(struct seq_buf s, const char str)
	{
	size_t len = strlen(str);

	WARN_ON(s->size == 0);

	/* Add 1 to len for the trailing null byte which must be there */
	len += 1;

	if (seq_buf_can_fit(s, len)) {
	memcpy(s->buffer + s->len, str, len);
	/* Don't count the trailing null byte against the capacity */
	s->len += len - 1;
	return 0;
	}
	seq_buf_set_overflow(s);
	return -1;
	}
	EXPORT_SYMBOL_GPL(seq_buf_puts);

	/**
	* seq_buf_putc - sequence printing of simple character
	* @s: seq_buf descriptor
	* @c: simple character to record
	*
	* Copy a single character into the sequence buffer.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_putc(struct seq_buf *s, unsigned char c)
	{
	WARN_ON(s->size == 0);

	if (seq_buf_can_fit(s, 1)) {
	s->buffer[s->len++] = c;
	return 0;
	}
	seq_buf_set_overflow(s);
	return -1;
	}
	EXPORT_SYMBOL_GPL(seq_buf_putc);

	/**
	* seq_buf_putmem - write raw data into the sequence buffer
	* @s: seq_buf descriptor
	* @mem: The raw memory to copy into the buffer
	* @len: The length of the raw memory to copy (in bytes)
	*
	* There may be cases where raw memory needs to be written into the
	* buffer and a strcpy() would not work. Using this function allows
	* for such cases.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_putmem(struct seq_buf s, const void mem, unsigned int len)
	{
	WARN_ON(s->size == 0);

	if (seq_buf_can_fit(s, len)) {
	memcpy(s->buffer + s->len, mem, len);
	s->len += len;
	return 0;
	}
	seq_buf_set_overflow(s);
	return -1;
	}

	#define MAX_MEMHEX_BYTES 8U
	#define HEX_CHARS (MAX_MEMHEX_BYTES*2 + 1)

	/**
	* seq_buf_putmem_hex - write raw memory into the buffer in ASCII hex
	* @s: seq_buf descriptor
	* @mem: The raw memory to write its hex ASCII representation of
	* @len: The length of the raw memory to copy (in bytes)
	*
	* This is similar to seq_buf_putmem() except instead of just copying the
	* raw memory into the buffer it writes its ASCII representation of it
	* in hex characters.
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_putmem_hex(struct seq_buf s, const void mem,
	unsigned int len)
	{
	unsigned char hex[HEX_CHARS];
	const unsigned char *data = mem;
	unsigned int start_len;
	int i, j;

	WARN_ON(s->size == 0);

	BUILD_BUG_ON(MAX_MEMHEX_BYTES * 2 >= HEX_CHARS);

	while (len) {
	start_len = min(len, MAX_MEMHEX_BYTES);
	#ifdef __BIG_ENDIAN
	for (i = 0, j = 0; i < start_len; i++) {
	#else
	for (i = start_len-1, j = 0; i >= 0; i--) {
	#endif
	hex[j++] = hex_asc_hi(data[i]);
	hex[j++] = hex_asc_lo(data[i]);
	}
	if (WARN_ON_ONCE(j == 0 \|\| j/2 > len))
	break;

	/* j increments twice per loop */
	hex[j++] = ' ';

	seq_buf_putmem(s, hex, j);
	if (seq_buf_has_overflowed(s))
	return -1;

	len -= start_len;
	data += start_len;
	}
	return 0;
	}

	/**
	* seq_buf_path - copy a path into the sequence buffer
	* @s: seq_buf descriptor
	* @path: path to write into the sequence buffer.
	* @esc: set of characters to escape in the output
	*
	* Write a path name into the sequence buffer.
	*
	* Returns: the number of written bytes on success, -1 on overflow.
	*/
	int seq_buf_path(struct seq_buf s, const struct path path, const char *esc)
	{
	char *buf;
	size_t size = seq_buf_get_buf(s, &buf);
	int res = -1;

	WARN_ON(s->size == 0);

	if (size) {
	char *p = d_path(path, buf, size);
	if (!IS_ERR(p)) {
	char *end = mangle_path(buf, p, esc);
	if (end)
	res = end - buf;
	}
	}
	seq_buf_commit(s, res);

	return res;
	}

	/**
	* seq_buf_to_user - copy the sequence buffer to user space
	* @s: seq_buf descriptor
	* @ubuf: The userspace memory location to copy to
	* @start: The first byte in the buffer to copy
	* @cnt: The amount to copy
	*
	* Copies the sequence buffer into the userspace memory pointed to
	* by @ubuf. It starts from @start and writes up to @cnt characters
	* or until it reaches the end of the content in the buffer (@s->len),
	* whichever comes first.
	*
	* Returns:
	* On success, it returns a positive number of the number of bytes
	* it copied.
	*
	* On failure it returns -EBUSY if all of the content in the
	* sequence has been already read, which includes nothing in the
	* sequence (@s->len == @start).
	*
	* Returns -EFAULT if the copy to userspace fails.
	*/
	int seq_buf_to_user(struct seq_buf s, char __user ubuf, size_t start, int cnt)
	{
	int len;
	int ret;

	if (!cnt)
	return 0;

	len = seq_buf_used(s);

	if (len <= start)
	return -EBUSY;

	len -= start;
	if (cnt > len)
	cnt = len;
	ret = copy_to_user(ubuf, s->buffer + start, cnt);
	if (ret == cnt)
	return -EFAULT;

	return cnt - ret;
	}

	/**
	* seq_buf_hex_dump - print formatted hex dump into the sequence buffer
	* @s: seq_buf descriptor
	* @prefix_str: string to prefix each line with;
	* caller supplies trailing spaces for alignment if desired
	* @prefix_type: controls whether prefix of an offset, address, or none
	* is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
	* @rowsize: number of bytes to print per line; must be 16 or 32
	* @groupsize: number of bytes to print at a time (1, 2, 4, 8; default = 1)
	* @buf: data blob to dump
	* @len: number of bytes in the @buf
	* @ascii: include ASCII after the hex output
	*
	* Function is an analogue of print_hex_dump() and thus has similar interface.
	*
	* linebuf size is maximal length for one line.
	* 32 * 3 - maximum bytes per line, each printed into 2 chars + 1 for
	* separating space
	* 2 - spaces separating hex dump and ASCII representation
	* 32 - ASCII representation
	* 1 - terminating '\0'
	*
	* Returns: zero on success, -1 on overflow.
	*/
	int seq_buf_hex_dump(struct seq_buf s, const char prefix_str, int prefix_type,
	int rowsize, int groupsize,
	const void *buf, size_t len, bool ascii)
	{
	const u8 *ptr = buf;
	int i, linelen, remaining = len;
	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
	int ret;

	if (rowsize != 16 && rowsize != 32)
	rowsize = 16;

	for (i = 0; i < len; i += rowsize) {
	linelen = min(remaining, rowsize);
	remaining -= rowsize;

	hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
	linebuf, sizeof(linebuf), ascii);

	switch (prefix_type) {
	case DUMP_PREFIX_ADDRESS:
	ret = seq_buf_printf(s, "%s%p: %s\n",
	prefix_str, ptr + i, linebuf);
	break;
	case DUMP_PREFIX_OFFSET:
	ret = seq_buf_printf(s, "%s%.8x: %s\n",
	prefix_str, i, linebuf);
	break;
	default:
	ret = seq_buf_printf(s, "%s%s\n", prefix_str, linebuf);
	break;
	}
	if (ret)
	return ret;
	}
	return 0;
	}