tpm2-tools源码分析之tpm2_verifysignature.c（2）

接前一篇文章：tpm2-tools源码分析之tpm2_verifysignature.c（1）

本文对tpm2_verifysignature.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) {

    const struct option topts[] = {
            { "digest",         required_argument, NULL, 'd' },
            { "hash-algorithm", required_argument, NULL, 'g' },
            { "message",        required_argument, NULL, 'm' },
            { "format",         required_argument, NULL,  0  },
            { "scheme",         required_argument, NULL, 'f' },
            { "signature",      required_argument, NULL, 's' },
            { "ticket",         required_argument, NULL, 't' },
            { "key-context",    required_argument, NULL, 'c' },
    };


    *opts = tpm2_options_new("g:m:d:f:s:t:c:", ARRAY_LEN(topts), topts,
            on_option, NULL, 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_verifysignature.c）中，如下：

static bool on_option(char key, char *value) {

    switch (key) {
    case 'c':
        ctx.context_arg = value;
        break;
    case 'g': {
        ctx.halg = tpm2_alg_util_from_optarg(value, tpm2_alg_util_flags_hash);
        if (ctx.halg == TPM2_ALG_ERROR) {
            LOG_ERR("Unable to convert algorithm, got: \"%s\"", value);
            return false;
        }
        ctx.flags.halg = 1;
    }
        break;
    case 'm': {
        ctx.msg_file_path = value;
        ctx.flags.msg = 1;
    }
        break;
    case 'd': {
        ctx.msg_hash = malloc(sizeof(TPM2B_DIGEST));
        ctx.msg_hash->size = sizeof(ctx.msg_hash->buffer);
        if (!files_load_bytes_from_path(value, ctx.msg_hash->buffer,
                &ctx.msg_hash->size)) {
            LOG_ERR("Could not load digest from file!");
            return false;
        }
        ctx.flags.digest = 1;
    }
        break;
    case 0:
	LOG_WARN("Option \"--format\" is deprecated, use \"--scheme\"");
        /* falls through */
    case 'f':
        ctx.format = tpm2_alg_util_from_optarg(value, tpm2_alg_util_flags_sig);
        if (ctx.format == TPM2_ALG_ERROR) {
            LOG_ERR("Unknown signing scheme, got: \"%s\"", value);
            return false;
        }

        ctx.flags.fmt = 1;
        break;
    case 's':
        ctx.sig_file_path = value;
        ctx.flags.sig = 1;
        break;
    case 't':
        ctx.out_file_path = value;
        ctx.flags.ticket = 1;
        break;
        /* no default */
    }

    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_verifysignature命令的说明相结合来看。tpm2_verifysignature命令的详细说明参见：

tpm2-tools/tpm2_verifysignature.1.md at master · tpm2-software/tpm2-tools · GitHub

下载了源码后，在tpm2-tools/man/tpm2_verifysignature.1.md中。

其中的参数说明如下：

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_verifysignature.c中的tpm2_tool_onstart函数就基本分析完了。