console_setup

对于boot参数 set bootargs root=/dev/ram0 rw init=/linuxrc mem=64M console=ttyS0,115200 lpj=4188160 user_debug=31 console=tty0 ecb_bootflags=1

/*
 * Set up a list of consoles.  Called from init/main.c
 */
static int __init console_setup(char *str)
{
    char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
    char *s, *options, *brl_options = NULL;
    int idx;

#ifdef CONFIG_A11Y_BRAILLE_CONSOLE//无定义
    if (!memcmp(str, "brl,", 4)) {
        brl_options = "";
        str += 4;
    } else if (!memcmp(str, "brl=", 4)) {
        brl_options = str + 4;
        str = strchr(brl_options, ',');
        if (!str) {
            printk(KERN_ERR "need port name after brl=\n");
            return 1;
        }
        *(str++) = 0;
    }
#endif

    /*
     * Decode str into name, index, options.
     */
    if (str[0] >= '0' && str[0] <= '9') {
        strcpy(buf, "ttyS");
        strncpy(buf + 4, str, sizeof(buf) - 5);
    } else {
        strncpy(buf, str, sizeof(buf) - 1);
    }
    buf[sizeof(buf) - 1] = 0;//第一次buf为ttyS0,115200
    if ((options = strchr(str, ',')) != NULL)
        *(options++) = 0;//options为115200
#ifdef __sparc__
    if (!strcmp(str, "ttya"))
        strcpy(buf, "ttyS0");
    if (!strcmp(str, "ttyb"))
        strcpy(buf, "ttyS1");
#endif
    for (s = buf; *s; s++)
        if ((*s >= '0' && *s <= '9') || *s == ',')
            break;
    idx = simple_strtoul(s, NULL, 10);//s指向"ttyS0"的‘0’，所以idx=0
    *s = 0;
//此时buf为ｔｔｙＳ，ｉｄｘ＝０，ｏｐｔｉｏｎｓ＝＂１１５２００＂，brl_options为ｎｕｌｌ
    __add_preferred_console(buf, idx, options, brl_options);
    console_set_on_cmdline = 1;
    return 1;
}
__setup("console=", console_setup);

两次调用console_setup输出如下：
buf=ttyS,idx=0,optinos=115200, brl_options=

buf=tty,idx=0,optinos=, brl_options=

static int __add_preferred_console(char *name, int idx, char *options,
                   char *brl_options)
{
    struct console_cmdline *c;
    int i;

    /*
     *    See if this tty is not yet registered, and
     *    if we have a slot free.
     */
    for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
        if (strcmp(console_cmdline[i].name, name) == 0 &&
              console_cmdline[i].index == idx) {
                if (!brl_options)
                    selected_console = i;
                return 0;
        }
    if (i == MAX_CMDLINECONSOLES)
        return -E2BIG;
    if (!brl_options)
        selected_console = i;／／两次ｉ分别为０和１，所以selected_console＝１
    c = &console_cmdline[i];
    strlcpy(c->name, name, sizeof(c->name));
    c->options = options;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
    c->brl_options = brl_options;
#endif
    c->index = idx;
    return 0;
}