xref: /freebsd/sys/dev/bhnd/nvram/bhnd_nvram_data_tlv.c (revision 685dc743dc3b5645e34836464128e1c0558b404b)

/*-
 * Copyright (c) 2016 Landon Fuller <landonf@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce at minimum a disclaimer
 *    similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
 *    redistribution must be conditioned upon including a substantially
 *    similar Disclaimer requirement for further binary redistribution.
 *
 * NO WARRANTY
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGES.
 */

#include <sys/cdefs.h>
#ifdef _KERNEL
#include <sys/param.h>
#include <sys/ctype.h>
#include <sys/limits.h>
#include <sys/malloc.h>
#include <sys/systm.h>
#else /* !_KERNEL */
#include <ctype.h>
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#endif /* _KERNEL */

#include "bhnd_nvram_private.h"

#include "bhnd_nvram_datavar.h"

#include "bhnd_nvram_data_tlvreg.h"

/*
 * CFE TLV NVRAM data class.
 *
 * The CFE-defined TLV NVRAM format is used on the WGT634U.
 */

struct bhnd_nvram_tlv {
	struct bhnd_nvram_data	 nv;	/**< common instance state */
	struct bhnd_nvram_io	*data;	/**< backing buffer */
	size_t			 count;	/**< variable count */
};

BHND_NVRAM_DATA_CLASS_DEFN(tlv, "WGT634U", BHND_NVRAM_DATA_CAP_DEVPATHS,
    sizeof(struct bhnd_nvram_tlv))

/** Minimal TLV_ENV record header */
struct bhnd_nvram_tlv_env_hdr {
	uint8_t		tag;
	uint8_t		size;
} __packed;

/** Minimal TLV_ENV record */
struct bhnd_nvram_tlv_env {
	struct bhnd_nvram_tlv_env_hdr	hdr;
	uint8_t				flags;
	char				envp[];
} __packed;

/* Return the length in bytes of an TLV_ENV's envp data */
#define	NVRAM_TLV_ENVP_DATA_LEN(_env)	\
	(((_env)->hdr.size < sizeof((_env)->flags)) ? 0 :	\
	    ((_env)->hdr.size - sizeof((_env)->flags)))

/* Maximum supported length of the envp data field, in bytes */
#define	NVRAM_TLV_ENVP_DATA_MAX_LEN	\
	(UINT8_MAX - sizeof(uint8_t) /* flags */)

static int				 bhnd_nvram_tlv_parse_size(
					     struct bhnd_nvram_io *io,
					     size_t *size);

static int				 bhnd_nvram_tlv_next_record(
					     struct bhnd_nvram_io *io,
					     size_t *next, size_t *offset,
					     uint8_t *tag);

static struct bhnd_nvram_tlv_env	*bhnd_nvram_tlv_next_env(
					     struct bhnd_nvram_tlv *tlv,
					     size_t *next, void **cookiep);

static struct bhnd_nvram_tlv_env	*bhnd_nvram_tlv_get_env(
					     struct bhnd_nvram_tlv *tlv,
					     void *cookiep);

static void				*bhnd_nvram_tlv_to_cookie(
					     struct bhnd_nvram_tlv *tlv,
					     size_t io_offset);
static size_t				 bhnd_nvram_tlv_to_offset(
					     struct bhnd_nvram_tlv *tlv,
					     void *cookiep);

static int
bhnd_nvram_tlv_probe(struct bhnd_nvram_io *io)
{
	struct bhnd_nvram_tlv_env	ident;
	size_t				nbytes;
	int				error;

	nbytes = bhnd_nvram_io_getsize(io);

	/* Handle what might be an empty TLV image */
	if (nbytes < sizeof(ident)) {
		uint8_t tag;

		/* Fetch just the first tag */
		error = bhnd_nvram_io_read(io, 0x0, &tag, sizeof(tag));
		if (error)
			return (error);

		/* This *could* be an empty TLV image, but all we're
		 * testing for here is a single 0x0 byte followed by EOF */
		if (tag == NVRAM_TLV_TYPE_END)
			return (BHND_NVRAM_DATA_PROBE_MAYBE);

		return (ENXIO);
	}

	/* Otherwise, look at the initial header for a valid TLV ENV tag,
	 * plus one byte of the entry data */
	error = bhnd_nvram_io_read(io, 0x0, &ident,
	    sizeof(ident) + sizeof(ident.envp[0]));
	if (error)
		return (error);

	/* First entry should be a variable record (which we statically
	 * assert as being defined to use a single byte size field) */
	if (ident.hdr.tag != NVRAM_TLV_TYPE_ENV)
		return (ENXIO);

	_Static_assert(NVRAM_TLV_TYPE_ENV & NVRAM_TLV_TF_U8_LEN,
	    "TYPE_ENV is not a U8-sized field");

	/* The entry must be at least 3 characters ('x=\0') in length */
	if (ident.hdr.size < 3)
		return (ENXIO);

	/* The first character should be a valid key char (alpha) */
	if (!bhnd_nv_isalpha(ident.envp[0]))
		return (ENXIO);

	return (BHND_NVRAM_DATA_PROBE_DEFAULT);
}

static int
bhnd_nvram_tlv_getvar_direct(struct bhnd_nvram_io *io, const char *name,
    void *buf, size_t *len, bhnd_nvram_type type)
{
	struct bhnd_nvram_tlv_env	 env;
	char				 data[NVRAM_TLV_ENVP_DATA_MAX_LEN];
	size_t				 data_len;
	const char			*key, *value;
	size_t				 keylen, vlen;
	size_t				 namelen;
	size_t				 next, off;
	uint8_t				 tag;
	int				 error;

	namelen = strlen(name);

	/* Iterate over the input looking for the requested variable */
	next = 0;
	while (!(error = bhnd_nvram_tlv_next_record(io, &next, &off, &tag))) {
		switch (tag) {
		case NVRAM_TLV_TYPE_END:
			/* Not found */
			return (ENOENT);

		case NVRAM_TLV_TYPE_ENV:
			/* Read the record header */
			error = bhnd_nvram_io_read(io, off, &env, sizeof(env));
			if (error) {
				BHND_NV_LOG("error reading TLV_ENV record "
				    "header: %d\n", error);
				return (error);
			}

			/* Read the record data */
			data_len = NVRAM_TLV_ENVP_DATA_LEN(&env);
			error = bhnd_nvram_io_read(io, off + sizeof(env), data,
			    data_len);
			if (error) {
				BHND_NV_LOG("error reading TLV_ENV record "
				    "data: %d\n", error);
				return (error);
			}

			/* Parse the key=value string */
			error = bhnd_nvram_parse_env(data, data_len, '=', &key,
			    &keylen, &value, &vlen);
			if (error) {
				BHND_NV_LOG("error parsing TLV_ENV data: %d\n",
				    error);
				return (error);
			}

			/* Match against requested variable name */
			if (keylen == namelen &&
			    strncmp(key, name, namelen) == 0)
			{
				return (bhnd_nvram_value_coerce(value, vlen,
				    BHND_NVRAM_TYPE_STRING, buf, len, type));
			}

			break;

		default:
			/* Skip unknown tags */
			break;
		}
	}

	/* Hit I/O error */
	return (error);
}

static int
bhnd_nvram_tlv_serialize(bhnd_nvram_data_class *cls, bhnd_nvram_plist *props,
    bhnd_nvram_plist *options, void *outp, size_t *olen)
{
	bhnd_nvram_prop	*prop;
	size_t		 limit, nbytes;
	int		 error;

	/* Determine output byte limit */
	if (outp != NULL)
		limit = *olen;
	else
		limit = 0;

	nbytes = 0;

	/* Write all properties */
	prop = NULL;
	while ((prop = bhnd_nvram_plist_next(props, prop)) != NULL) {
		struct bhnd_nvram_tlv_env	 env;
		const char			*name;
		uint8_t				*p;
		size_t				 name_len, value_len;
		size_t				 rec_size;

		env.hdr.tag = NVRAM_TLV_TYPE_ENV;
		env.hdr.size = sizeof(env.flags);
		env.flags = 0x0;

		/* Fetch name value and add to record length */
		name = bhnd_nvram_prop_name(prop);
		name_len = strlen(name) + 1 /* '=' */;

		if (UINT8_MAX - env.hdr.size < name_len) {
			BHND_NV_LOG("%s name exceeds maximum TLV record "
			    "length\n", name);
			return (EFTYPE); /* would overflow TLV size */
		}

		env.hdr.size += name_len;

		/* Add string value to record length */
		error = bhnd_nvram_prop_encode(prop, NULL, &value_len,
		    BHND_NVRAM_TYPE_STRING);
		if (error) {
			BHND_NV_LOG("error serializing %s to required type "
			    "%s: %d\n", name,
			    bhnd_nvram_type_name(BHND_NVRAM_TYPE_STRING),
			    error);
			return (error);
		}

		if (UINT8_MAX - env.hdr.size < value_len) {
			BHND_NV_LOG("%s value exceeds maximum TLV record "
			    "length\n", name);
			return (EFTYPE); /* would overflow TLV size */
		}

		env.hdr.size += value_len;

		/* Calculate total record size */
		rec_size = sizeof(env.hdr) + env.hdr.size;
		if (SIZE_MAX - nbytes < rec_size)
			return (EFTYPE); /* would overflow size_t */

		/* Calculate our output pointer */
		if (nbytes > limit || limit - nbytes < rec_size) {
			/* buffer is full; cannot write */
			p = NULL;
		} else {
			p = (uint8_t *)outp + nbytes;
		}

		/* Write to output */
		if (p != NULL) {
			memcpy(p, &env, sizeof(env));
			p += sizeof(env);

			memcpy(p, name, name_len - 1);
			p[name_len - 1] = '=';
			p += name_len;

			error = bhnd_nvram_prop_encode(prop, p, &value_len,
			    BHND_NVRAM_TYPE_STRING);
			if (error) {
				BHND_NV_LOG("error serializing %s to required "
				    "type %s: %d\n", name,
				    bhnd_nvram_type_name(
					BHND_NVRAM_TYPE_STRING),
				    error);
				return (error);
			}
		}

		nbytes += rec_size;
	}

	/* Write terminating END record */
	if (limit > nbytes)
		*((uint8_t *)outp + nbytes) = NVRAM_TLV_TYPE_END;

	if (nbytes == SIZE_MAX)
		return (EFTYPE); /* would overflow size_t */
	nbytes++;

	/* Provide required length */
	*olen = nbytes;
	if (limit < *olen) {
		if (outp == NULL)
			return (0);

		return (ENOMEM);
	}

	return (0);
}

/**
 * Initialize @p tlv with the provided NVRAM TLV data mapped by @p src.
 *
 * @param tlv A newly allocated data instance.
 */
static int
bhnd_nvram_tlv_init(struct bhnd_nvram_tlv *tlv, struct bhnd_nvram_io *src)
{
	struct bhnd_nvram_tlv_env	*env;
	size_t				 size;
	size_t				 next;
	int				 error;

	BHND_NV_ASSERT(tlv->data == NULL, ("tlv data already initialized"));

	/* Determine the actual size of the TLV source data */
	if ((error = bhnd_nvram_tlv_parse_size(src, &size)))
		return (error);

	/* Copy to our own internal buffer */
	if ((tlv->data = bhnd_nvram_iobuf_copy_range(src, 0x0, size)) == NULL)
		return (ENOMEM);

	/* Initialize our backing buffer */
	tlv->count = 0;
	next = 0;
	while ((env = bhnd_nvram_tlv_next_env(tlv, &next, NULL)) != NULL) {
		size_t env_len;
		size_t name_len;

		/* TLV_ENV data must not be empty */
		env_len = NVRAM_TLV_ENVP_DATA_LEN(env);
		if (env_len == 0) {
			BHND_NV_LOG("cannot parse zero-length TLV_ENV record "
			    "data\n");
			return (EINVAL);
		}

		/* Parse the key=value string, and then replace the '='
		 * delimiter with '\0' to allow us to provide direct
		 * name pointers from our backing buffer */
		error = bhnd_nvram_parse_env(env->envp, env_len, '=', NULL,
		    &name_len, NULL, NULL);
		if (error) {
			BHND_NV_LOG("error parsing TLV_ENV data: %d\n", error);
			return (error);
		}

		/* Replace '=' with '\0' */
		*(env->envp + name_len) = '\0';

		/* Add to variable count */
		tlv->count++;
	};

	return (0);
}

static int
bhnd_nvram_tlv_new(struct bhnd_nvram_data *nv, struct bhnd_nvram_io *io)
{

	struct bhnd_nvram_tlv	*tlv;
	int			 error;

	/* Allocate and initialize the TLV data instance */
	tlv = (struct bhnd_nvram_tlv *)nv;

	/* Parse the TLV input data and initialize our backing
	 * data representation */
	if ((error = bhnd_nvram_tlv_init(tlv, io))) {
		bhnd_nvram_tlv_free(nv);
		return (error);
	}

	return (0);
}

static void
bhnd_nvram_tlv_free(struct bhnd_nvram_data *nv)
{
	struct bhnd_nvram_tlv *tlv = (struct bhnd_nvram_tlv *)nv;
	if (tlv->data != NULL)
		bhnd_nvram_io_free(tlv->data);
}

size_t
bhnd_nvram_tlv_count(struct bhnd_nvram_data *nv)
{
	struct bhnd_nvram_tlv *tlv = (struct bhnd_nvram_tlv *)nv;
	return (tlv->count);
}

static bhnd_nvram_plist *
bhnd_nvram_tlv_options(struct bhnd_nvram_data *nv)
{
	return (NULL);
}

static uint32_t
bhnd_nvram_tlv_caps(struct bhnd_nvram_data *nv)
{
	return (BHND_NVRAM_DATA_CAP_READ_PTR|BHND_NVRAM_DATA_CAP_DEVPATHS);
}

static const char *
bhnd_nvram_tlv_next(struct bhnd_nvram_data *nv, void **cookiep)
{
	struct bhnd_nvram_tlv		*tlv;
	struct bhnd_nvram_tlv_env	*env;
	size_t				 io_offset;

	tlv = (struct bhnd_nvram_tlv *)nv;

	/* Find next readable TLV record */
	if (*cookiep == NULL) {
		/* Start search at offset 0x0 */
		io_offset = 0x0;
		env = bhnd_nvram_tlv_next_env(tlv, &io_offset, cookiep);
	} else {
		/* Seek past the previous env record */
		io_offset = bhnd_nvram_tlv_to_offset(tlv, *cookiep);
		env = bhnd_nvram_tlv_next_env(tlv, &io_offset, NULL);
		if (env == NULL)
			BHND_NV_PANIC("invalid cookiep; record missing");

		/* Advance to next env record, update the caller's cookiep */
		env = bhnd_nvram_tlv_next_env(tlv, &io_offset, cookiep);
	}

	/* Check for EOF */
	if (env == NULL)
		return (NULL);

	/* Return the NUL terminated name */
	return (env->envp);
}

static void *
bhnd_nvram_tlv_find(struct bhnd_nvram_data *nv, const char *name)
{
	return (bhnd_nvram_data_generic_find(nv, name));
}

static int
bhnd_nvram_tlv_getvar_order(struct bhnd_nvram_data *nv, void *cookiep1,
    void *cookiep2)
{
	if (cookiep1 < cookiep2)
		return (-1);

	if (cookiep1 > cookiep2)
		return (1);

	return (0);
}

static int
bhnd_nvram_tlv_getvar(struct bhnd_nvram_data *nv, void *cookiep, void *buf,
    size_t *len, bhnd_nvram_type type)
{
	return (bhnd_nvram_data_generic_rp_getvar(nv, cookiep, buf, len, type));
}

static int
bhnd_nvram_tlv_copy_val(struct bhnd_nvram_data *nv, void *cookiep,
    bhnd_nvram_val **value)
{
	return (bhnd_nvram_data_generic_rp_copy_val(nv, cookiep, value));
}

static const void *
bhnd_nvram_tlv_getvar_ptr(struct bhnd_nvram_data *nv, void *cookiep,
    size_t *len, bhnd_nvram_type *type)
{
	struct bhnd_nvram_tlv		*tlv;
	struct bhnd_nvram_tlv_env	*env;
	const char			*val;
	int				 error;

	tlv = (struct bhnd_nvram_tlv *)nv;

	/* Fetch pointer to the TLV_ENV record */
	if ((env = bhnd_nvram_tlv_get_env(tlv, cookiep)) == NULL)
		BHND_NV_PANIC("invalid cookiep: %p", cookiep);

	/* Parse value pointer and length from key\0value data */
	error = bhnd_nvram_parse_env(env->envp, NVRAM_TLV_ENVP_DATA_LEN(env),
	    '\0', NULL, NULL, &val, len);
	if (error)
		BHND_NV_PANIC("unexpected error parsing '%s'", env->envp);

	/* Type is always CSTR */
	*type = BHND_NVRAM_TYPE_STRING;

	return (val);
}

static const char *
bhnd_nvram_tlv_getvar_name(struct bhnd_nvram_data *nv, void *cookiep)
{
	struct bhnd_nvram_tlv		*tlv;
	const struct bhnd_nvram_tlv_env	*env;

	tlv = (struct bhnd_nvram_tlv *)nv;

	/* Fetch pointer to the TLV_ENV record */
	if ((env = bhnd_nvram_tlv_get_env(tlv, cookiep)) == NULL)
		BHND_NV_PANIC("invalid cookiep: %p", cookiep);

	/* Return name pointer */
	return (&env->envp[0]);
}

static int
bhnd_nvram_tlv_filter_setvar(struct bhnd_nvram_data *nv, const char *name,
    bhnd_nvram_val *value, bhnd_nvram_val **result)
{
	bhnd_nvram_val	*str;
	const char	*inp;
	bhnd_nvram_type	 itype;
	size_t		 ilen;
	size_t		 name_len, tlv_nremain;
	int		 error;

	tlv_nremain = NVRAM_TLV_ENVP_DATA_MAX_LEN;

	/* Name (trimmed of any path prefix) must be valid */
	if (!bhnd_nvram_validate_name(bhnd_nvram_trim_path_name(name)))
		return (EINVAL);

	/* 'name=' must fit within the maximum TLV_ENV record length */
	name_len = strlen(name) + 1; /* '=' */
	if (tlv_nremain < name_len) {
		BHND_NV_LOG("'%s=' exceeds maximum TLV_ENV record length\n",
		    name);
		return (EINVAL);
	}
	tlv_nremain -= name_len;

	/* Convert value to a (bcm-formatted) string */
	error = bhnd_nvram_val_convert_new(&str, &bhnd_nvram_val_bcm_string_fmt,
	    value, BHND_NVRAM_VAL_DYNAMIC);
	if (error)
		return (error);

	/* The string value must fit within remaining TLV_ENV record length */
	inp = bhnd_nvram_val_bytes(str, &ilen, &itype);
	if (tlv_nremain < ilen) {
		BHND_NV_LOG("'%.*s\\0' exceeds maximum TLV_ENV record length\n",
		    BHND_NV_PRINT_WIDTH(ilen), inp);

		bhnd_nvram_val_release(str);
		return (EINVAL);
	}
	tlv_nremain -= name_len;

	/* Success. Transfer result ownership to the caller. */
	*result = str;
	return (0);
}

static int
bhnd_nvram_tlv_filter_unsetvar(struct bhnd_nvram_data *nv, const char *name)
{
	/* We permit deletion of any variable */
	return (0);
}

/**
 * Iterate over the records starting at @p next, returning the parsed
 * record's @p tag, @p size, and @p offset.
 *
 * @param		io		The I/O context to parse.
 * @param[in,out]	next		The next offset to be parsed, or 0x0
 *					to begin parsing. Upon successful
 *					return, will be set to the offset of the
 *					next record (or EOF, if
 *					NVRAM_TLV_TYPE_END was parsed).
 * @param[out]		offset		The record's value offset.
 * @param[out]		tag		The record's tag.
 *
 * @retval 0		success
 * @retval EINVAL	if parsing @p io as TLV fails.
 * @retval non-zero	if reading @p io otherwise fails, a regular unix error
 *			code will be returned.
 */
static int
bhnd_nvram_tlv_next_record(struct bhnd_nvram_io *io, size_t *next, size_t
    *offset, uint8_t *tag)
{
	size_t		io_offset, io_size;
	uint16_t	parsed_len;
	uint8_t		len_hdr[2];
	int		error;

	io_offset = *next;
	io_size = bhnd_nvram_io_getsize(io);

	/* Save the record offset */
	if (offset != NULL)
		*offset = io_offset;

	/* Fetch initial tag */
	error = bhnd_nvram_io_read(io, io_offset, tag, sizeof(*tag));
	if (error)
		return (error);
	io_offset++;

	/* EOF */
	if (*tag == NVRAM_TLV_TYPE_END) {
		*next = io_offset;
		return (0);
	}

	/* Read length field */
	if (*tag & NVRAM_TLV_TF_U8_LEN) {
		error = bhnd_nvram_io_read(io, io_offset, &len_hdr,
		    sizeof(len_hdr[0]));
		if (error) {
			BHND_NV_LOG("error reading TLV record size: %d\n",
			    error);
			return (error);
		}

		parsed_len = len_hdr[0];
		io_offset++;
	} else {
		error = bhnd_nvram_io_read(io, io_offset, &len_hdr,
		    sizeof(len_hdr));
		if (error) {
			BHND_NV_LOG("error reading 16-bit TLV record "
			    "size: %d\n", error);
			return (error);
		}

		parsed_len = (len_hdr[0] << 8) | len_hdr[1];
		io_offset += 2;
	}

	/* Advance to next record */
	if (parsed_len > io_size || io_size - parsed_len < io_offset) {
		/* Hit early EOF */
		BHND_NV_LOG("TLV record length %hu truncated by input "
		    "size of %zu\n", parsed_len, io_size);
		return (EINVAL);
	}

	*next = io_offset + parsed_len;

	/* Valid record found */
	return (0);
}

/**
 * Parse the TLV data in @p io to determine the total size of the TLV
 * data mapped by @p io (which may be less than the size of @p io).
 */
static int
bhnd_nvram_tlv_parse_size(struct bhnd_nvram_io *io, size_t *size)
{
	size_t		next;
	uint8_t		tag;
	int		error;

	/* We have to perform a minimal parse to determine the actual length */
	next = 0x0;
	*size = 0x0;

	/* Iterate over the input until we hit END tag or the read fails */
	do {
		error = bhnd_nvram_tlv_next_record(io, &next, NULL, &tag);
		if (error)
			return (error);
	} while (tag != NVRAM_TLV_TYPE_END);

	/* Offset should now point to EOF */
	BHND_NV_ASSERT(next <= bhnd_nvram_io_getsize(io),
	    ("parse returned invalid EOF offset"));

	*size = next;
	return (0);
}

/**
 * Iterate over the records in @p tlv, returning a pointer to the next
 * NVRAM_TLV_TYPE_ENV record, or NULL if EOF is reached.
 *
 * @param		tlv		The TLV instance.
 * @param[in,out]	next		The next offset to be parsed, or 0x0
 *					to begin parsing. Upon successful
 *					return, will be set to the offset of the
 *					next record.
 */
static struct bhnd_nvram_tlv_env *
bhnd_nvram_tlv_next_env(struct bhnd_nvram_tlv *tlv, size_t *next,
    void **cookiep)
{
	uint8_t	tag;
	int	error;

	/* Find the next TLV_ENV record, starting at @p next */
	do {
		void	*c;
		size_t	 offset;

		/* Fetch the next TLV record */
		error = bhnd_nvram_tlv_next_record(tlv->data, next, &offset,
		    &tag);
		if (error) {
			BHND_NV_LOG("unexpected error in next_record(): %d\n",
			    error);
			return (NULL);
		}

		/* Only interested in ENV records */
		if (tag != NVRAM_TLV_TYPE_ENV)
			continue;

		/* Map and return TLV_ENV record pointer */
		c = bhnd_nvram_tlv_to_cookie(tlv, offset);

		/* Provide the cookiep value for the returned record */
		if (cookiep != NULL)
			*cookiep = c;

		return (bhnd_nvram_tlv_get_env(tlv, c));
	} while (tag != NVRAM_TLV_TYPE_END);

	/* No remaining ENV records */
	return (NULL);
}

/**
 * Return a pointer to the TLV_ENV record for @p cookiep, or NULL
 * if none vailable.
 */
static struct bhnd_nvram_tlv_env *
bhnd_nvram_tlv_get_env(struct bhnd_nvram_tlv *tlv, void *cookiep)
{
	struct bhnd_nvram_tlv_env	*env;
	void				*ptr;
	size_t				 navail;
	size_t				 io_offset, io_size;
	int				 error;

	io_size = bhnd_nvram_io_getsize(tlv->data);
	io_offset = bhnd_nvram_tlv_to_offset(tlv, cookiep);

	/* At EOF? */
	if (io_offset == io_size)
		return (NULL);

	/* Fetch non-const pointer to the record entry */
	error = bhnd_nvram_io_write_ptr(tlv->data, io_offset, &ptr,
	    sizeof(env->hdr), &navail);
	if (error) {
		/* Should never occur with a valid cookiep */
		BHND_NV_LOG("error mapping record for cookiep: %d\n", error);
		return (NULL);
	}

	/* Validate the record pointer */
	env = ptr;
	if (env->hdr.tag != NVRAM_TLV_TYPE_ENV) {
		/* Should never occur with a valid cookiep */
		BHND_NV_LOG("non-ENV record mapped for %p\n", cookiep);
		return (NULL);
	}

	/* Is the required variable name data is mapped? */
	if (navail < sizeof(struct bhnd_nvram_tlv_env_hdr) + env->hdr.size ||
	    env->hdr.size == sizeof(env->flags))
	{
		/* Should never occur with a valid cookiep */
		BHND_NV_LOG("TLV_ENV variable data not mapped for %p\n",
		    cookiep);
		return (NULL);
	}

	return (env);
}

/**
 * Return a cookiep for the given I/O offset.
 */
static void *
bhnd_nvram_tlv_to_cookie(struct bhnd_nvram_tlv *tlv, size_t io_offset)
{
	const void	*ptr;
	int		 error;

	BHND_NV_ASSERT(io_offset < bhnd_nvram_io_getsize(tlv->data),
	    ("io_offset %zu out-of-range", io_offset));
	BHND_NV_ASSERT(io_offset < UINTPTR_MAX,
	    ("io_offset %#zx exceeds UINTPTR_MAX", io_offset));

	error = bhnd_nvram_io_read_ptr(tlv->data, 0x0, &ptr, io_offset, NULL);
	if (error)
		BHND_NV_PANIC("error mapping offset %zu: %d", io_offset, error);

	ptr = (const uint8_t *)ptr + io_offset;
	return (__DECONST(void *, ptr));
}

/* Convert a cookiep back to an I/O offset */
static size_t
bhnd_nvram_tlv_to_offset(struct bhnd_nvram_tlv *tlv, void *cookiep)
{
	const void	*ptr;
	intptr_t	 offset;
	size_t		 io_size;
	int		 error;

	BHND_NV_ASSERT(cookiep != NULL, ("null cookiep"));

	io_size = bhnd_nvram_io_getsize(tlv->data);

	error = bhnd_nvram_io_read_ptr(tlv->data, 0x0, &ptr, io_size, NULL);
	if (error)
		BHND_NV_PANIC("error mapping offset %zu: %d", io_size, error);

	offset = (const uint8_t *)cookiep - (const uint8_t *)ptr;
	BHND_NV_ASSERT(offset >= 0, ("invalid cookiep"));
	BHND_NV_ASSERT((uintptr_t)offset < SIZE_MAX, ("cookiep > SIZE_MAX)"));
	BHND_NV_ASSERT((uintptr_t)offset <= io_size, ("cookiep > io_size)"));

	return ((size_t)offset);
}