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lsusb: Split out routine that fetches value for given field.

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Field value lookup was done in multiple places, so it's useful
as a helper function.

Signed-off-by: Michael Drake <michael.drake@codethink.co.uk>
This commit is contained in:
Michael Drake 2018-06-07 11:01:37 +01:00
parent 8e92109e03
commit e497fcd9d6
1 changed files with 58 additions and 48 deletions
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106
desc-dump.c
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@ -2,7 +2,7 @@
/*
* USB descriptor dumping
*
* Copyright (C) 2017 Michael Drake <michael.drake@codethink.co.uk>
* Copyright (C) 2017-2018 Michael Drake <michael.drake@codethink.co.uk>
*/
#include "config.h"
@ -109,6 +109,57 @@ static unsigned long long get_n_bytes_as_ull(
return ret;
}
/**
* Get the size of a descriptor field in bytes.
*
* Normally the size is provided in the entry's size parameter, but some
* fields have a variable size, with the actual size being stored in as
* the value of another field.
*
* \param[in] buf Descriptor data.
* \param[in] desc First field in the descriptor definition array.
* \param[in] entry The descriptor definition field to get size for.
* \return Size of the field in bytes.
*/
static unsigned int get_entry_size(
const unsigned char *buf,
const struct desc *desc,
const struct desc *entry);
/**
* Read a value from a field of given name.
*
* \param[in] buf Descriptor data.
* \param[in] desc First field in the descriptor definition array.
* \param[in] field The name of the field to get the value for.
* \return The value from the given field.
*/
static unsigned long long get_value_from_field(
const unsigned char *buf,
const struct desc *desc,
const char *field)
{
size_t offset = 0;
const struct desc *current;
unsigned long long value = 0;
/* Search descriptor definition array for the field who's value
* gives the value of the entry we're interested in. */
for (current = desc; current->field != NULL; current++) {
if (strcmp(current->field, field) == 0) {
value = get_n_bytes_as_ull(buf, offset,
current->size);
break;
}
/* Keep track of our offset in the descriptor data
* as we look for the field we want. */
offset += get_entry_size(buf, desc, current);
}
return value;
}
/**
* Dump a number as hex to stdout.
*
@ -270,18 +321,7 @@ static void value_renderer(
}
}
/**
* Get the size of a descriptor field in bytes.
*
* Normally the size is provided in the entry's size parameter, but some
* fields have a variable size, with the actual size being stored in as
* the value of another field.
*
* \param[in] buf Descriptor data.
* \param[in] desc First field in the descriptor definition array.
* \param[in] entry The descriptor definition field to get size for.
* \return Size of the field in bytes.
*/
/* Documented at forward declaration above. */
static unsigned int get_entry_size(
const unsigned char *buf,
const struct desc *desc,
@ -292,24 +332,7 @@ static unsigned int get_entry_size(
if (entry->size_field != NULL) {
/* Variable field length, given by `size_field`'s value. */
size_t offset = 0;
/* Search descriptor definition array for the field who's value
* gives the size of the entry we're interested in. */
for (current = desc; current->field != NULL; current++) {
if (strcmp(current->field, entry->size_field) == 0) {
/* Found the field who's value gives us the
* size of, so read that field's value out of
* the descriptor data buffer. */
size = get_n_bytes_as_ull(buf, offset,
current->size);
break;
}
/* Keep track of our offset in the descriptor data
* as we look for the field we want. */
offset += get_entry_size(buf, desc, current);
}
size = get_value_from_field(buf, desc, entry->size_field);
}
if (size == 0) {
@ -347,27 +370,14 @@ static unsigned int get_array_entry_count(
if (array_entry->array.length_field1) {
/* We can get the array size from the length_field1. */
size_t offset = 0;
for (current = desc; current->field != NULL; current++) {
if (strcmp(current->field, array_entry->array.length_field1) == 0) {
entries = get_n_bytes_as_ull(buf, offset, current->size);
break;
}
entries = get_value_from_field(buf, desc,
array_entry->array.length_field1);
offset += get_entry_size(buf, desc, current);
}
offset = 0; /* skip first three common 1-byte fields */
if (array_entry->array.length_field2 != NULL) {
/* There's a second field specifying length. The two
* lengths are multiplied. */
for (current = desc; current->field != NULL; current++) {
if (strcmp(current->field, array_entry->array.length_field2) == 0) {
entries *= get_n_bytes_as_ull(buf, offset, current->size);
break;
}
offset += get_entry_size(buf, desc, current);
}
entries *= get_value_from_field(buf, desc,
array_entry->array.length_field2);
}
/* If the bits flag is set, then the entry count so far