接前一篇文章:tpm2-tools源码分析之tpm2_hash.c(1)
本文对tpm2_hash.c中的tpm2_tool_onstart函数进行详细解析。
先再次贴出该函数源码:
static bool tpm2_tool_onstart(tpm2_options **opts) {
static struct option topts[] = {
{"hierarchy", required_argument, NULL, 'C'},
{"hash-algorithm", required_argument, NULL, 'g'},
{"output", required_argument, NULL, 'o'},
{"ticket", required_argument, NULL, 't'},
{"hex", no_argument, NULL, 0 },
};
/* set up non-static defaults here */
ctx.input_file = stdin;
*opts = tpm2_options_new("C:g:o:t:", ARRAY_LEN(topts), topts, on_option,
on_args, 0);
return *opts != NULL;
}
tpm2_options结构的定义在tpm2-tools/lib/tpm2_options.h中,代码如下:
struct tpm2_options {
struct {
tpm2_option_handler on_opt;
tpm2_arg_handler on_arg;
} callbacks;
char *short_opts;
size_t len;
uint32_t flags;
struct option long_opts[];
};
typedef struct tpm2_options tpm2_options;
struct option的定义在/usr/include/bits/getopt_ext.h中,代码如下:
struct option
{
const char *name;
/* has_arg can't be an enum because some compilers complain about
type mismatches in all the code that assumes it is an int. */
int has_arg;
int *flag;
int val;
};
on_option函数的实现在同文件(tools/tpm2_hash.c)中,如下:
static bool on_option(char key, char *value) {
bool res;
switch (key) {
case 'C':
res = tpm2_util_handle_from_optarg(value, &ctx.hierarchy_value,
TPM2_HANDLE_FLAGS_ALL_HIERACHIES);
if (!res) {
return false;
}
break;
case 'g':
ctx.halg = tpm2_alg_util_from_optarg(value, tpm2_alg_util_flags_hash);
if (ctx.halg == TPM2_ALG_ERROR) {
return false;
}
break;
case 'o':
ctx.output_hash_path = value;
break;
case 't':
ctx.output_ticket_path = value;
break;
case 0:
ctx.hex = true;
break;
}
return true;
}
要更好地理解这些选项乃至tpm2_tool_onstart函数的功能,需要与tpm2_hash命令的说明相结合来看。tpm2_hash命令的详细说明参见:
tpm2-tools/tpm2_hash.1.md at master · tpm2-software/tpm2-tools · GitHub
下载了源码后,在tpm2-tools/man/tpm2_hash.1.md中。
tpm2_options_new函数属于公共代码,在tpm2-tools/lib/tpm2_options.c中,代码如下:
tpm2_options *tpm2_options_new(const char *short_opts, size_t len,
const struct option *long_opts, tpm2_option_handler on_opt,
tpm2_arg_handler on_arg, uint32_t flags) {
tpm2_options *opts = calloc(1, sizeof(*opts) + (sizeof(*long_opts) * len));
if (!opts) {
LOG_ERR("oom");
return NULL;
}
/*
* On NULL, just make it a zero length string so we don't have to keep
* checking it for NULL.
*/
if (!short_opts) {
short_opts = "";
}
opts->short_opts = strdup(short_opts);
if (!opts->short_opts) {
LOG_ERR("oom");
free(opts);
return NULL;
}
opts->callbacks.on_opt = on_opt;
opts->callbacks.on_arg = on_arg;
opts->len = len;
opts->flags = flags;
memcpy(opts->long_opts, long_opts, len * sizeof(*long_opts));
return opts;
}
tpm2_new_options函数很容易理解,其功能是基于tpm2_tool_onstart函数中的struct option topts构建tpm2_options实例(*opts)。
至此,tpm2_hash.c中的tpm2_tool_onstart函数就基本分析完了。