接前一篇文章：tpm2-tools源码分析之tpm2_changeauth.c（1）

本文对tpm2_changeauth.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) {

    struct option topts[] = {
        { "object-auth",    required_argument, NULL, 'p' },
        { "object-context", required_argument, NULL, 'c' },
        { "parent-context", required_argument, NULL, 'C' },
        { "private",        required_argument, NULL, 'r' },
        { "cphash",         required_argument, NULL,  0  },
        { "rphash",         required_argument, NULL,  1  },
        { "session",        required_argument, NULL, 'S' },
    };
    *opts = tpm2_options_new("p:c:C:r:S:", ARRAY_LEN(topts), topts,
                             on_option, on_arg, 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_changeauth.c）中，如下：

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

    switch (key) {
    case 'c':
        ctx.object.ctx = value;
        break;
    case 'C':
        ctx.parent.ctx = value;
        break;
    case 'p':
        ctx.object.auth_current = value;
        break;
    case 'n':
        ctx.object.auth_new = value;
        break;
    case 'r':
        ctx.object.out_path = value;
        break;
    case 0:
        ctx.cp_hash_path = value;
        break;
    case 1:
        ctx.rp_hash_path = value;
        break;
    case 'S':
        ctx.aux_session_path[ctx.aux_session_cnt] = value;
        if (ctx.aux_session_cnt < MAX_AUX_SESSIONS) {
            ctx.aux_session_cnt++;
        } else {
            LOG_ERR("Specify a max of 3 sessions");
            return false;
        }
        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_changeauth命令的说明相结合来看。tpm2_changeauth命令的详细说明参见：

https://github.com/tpm2-software/tpm2-tools/blob/master/man/tpm2_changeauth.1.md

下载了源码后，在tpm2-tools/man/tpm2_changeauth.1.md中。

其中的参数说明如下：

OPTIONS

Passwords should follow the "password authorization formatting standards", see section "Authorization Formatting".

• -c, --object-context=OBJECT:

  The key context object to be used for the operation. —— 用于操作的密钥上下文对象。

• -p, --object-auth=AUTH:

  The old authorization value for the TPM object specified with -c. —— 用-c指定的TPM对象的旧授权值。

• -C, --parent-context=OBJECT:

  The parent object. This is required if the object for the operation is a transient or persistent object. —— 父对象。如果操作的对象是临时对象或持久对象，则需要这样做。

• -r, --private=FILE: The output file which contains the new sensitive portion of the object whose auth was being changed. —— 输出文件，其中包含正在更改其身份验证的对象的新的敏感部分。 protection details

• --cphash=FILE

  File path to record the hash of the command parameters. This is commonly termed as cpHash. NOTE: When this option is selected, The tool will not actually execute the command, it simply returns a cpHash, unless rphash is also required. —— 用于记录命令参数哈希的文件路径。这通常被称为cpHash。注意：当选择此选项时，该工具将不会实际执行命令，它只是返回一个cpHash，除非也需要rphash。

• --rphash=FILE

  File path to record the hash of the response parameters. This is commonly termed as rpHash. —— 用于记录响应参数哈希的文件路径。这通常被称为rpHash。

• -S, --session=FILE:

  The session created using tpm2_startauthsession. This can be used to specify an auxiliary session for auditing and or encryption/decryption of the parameters. —— 使用tpm2_startauthsession创建的会话。这可以用于指定用于参数的审计和/或加密/解密的辅助会话。

• ARGUMENT the command line argument specifies the AUTH to be set for the object specified with -c. —— 命令行参数指定的AUTH，此AUTH要为使用-c指定的对象设置。

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