printk实用功能

printk实用功能%pI4 打印IPV4地址%pI6 打印IPV6地址%pM 打印MAC地址/** * printk的解码部分实现 * 来源于lib/vsprintf.c文件 * * @param fmt 格式化参数 * @param spec * * @return */static int format_decode(const char *fmt, struct printf_spec *spec){const char *start = fmt;/* we finished early by reading the field width */if (spec->type == FORMAT_TYPE_WIDTH) {if (spec->field_width < 0) {spec->field_width = -spec->field_width;spec->flags |= LEFT;}spec->type = FORMAT_TYPE_NONE;goto precision;}/* we finished early by reading the precision */if (spec->type == FORMAT_TYPE_PRECISION) {if (spec->precision < 0)spec->precision = 0;spec->type = FORMAT_TYPE_NONE;goto qualifier;}/* By default */spec->type = FORMAT_TYPE_NONE;for (; *fmt ; ++fmt) {if (*fmt == '%')break;}/* Return the current non-format string */if (fmt != start || !*fmt)return fmt - start;/* Process flags */spec->flags = 0;while (1) { /* this also skips first '%' */bool found = true;++fmt;switch (*fmt) {case '-': spec->flags |= LEFT; break;case '+': spec->flags |= PLUS; break;case ' ': spec->flags |= SPACE; break;case '#': spec->flags |= SPECIAL; break;case '0': spec->flags |= ZEROPAD; break;default: found = false;}if (!found)break;}/* get field width */spec->field_width = -1;if (isdigit(*fmt))spec->field_width = skip_atoi(&fmt);else if (*fmt == '*') {/* it's the next argument */spec->type = FORMAT_TYPE_WIDTH;return ++fmt - start;}precision:/* get the precision */spec->precision = -1;if (*fmt == '.') {++fmt;if (isdigit(*fmt)) {spec->precision = skip_atoi(&fmt);if (spec->precision < 0)spec->precision = 0;} else if (*fmt == '*') {/* it's the next argument */spec->type = FORMAT_TYPE_PRECISION;return ++fmt - start;}}qualifier:/* get the conversion qualifier */spec->qualifier = -1;if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L' || *fmt == 'Z' || *fmt == 'z' || *fmt == 't') {spec->qualifier = *fmt;++fmt;if (spec->qualifier == 'l' && *fmt == 'l') {spec->qualifier = 'L';++fmt;}}/* default base */spec->base = 10;switch (*fmt) {case 'c':spec->type = FORMAT_TYPE_CHAR;return ++fmt - start;case 's':spec->type = FORMAT_TYPE_STR;return ++fmt - start;case 'p':spec->type = FORMAT_TYPE_PTR;return fmt - start;/* skip alnum */case 'n':spec->type = FORMAT_TYPE_NRCHARS;return ++fmt - start;case '%':spec->type = FORMAT_TYPE_PERCENT_CHAR;return ++fmt - start;/* integer number formats - set up the flags and "break" */case 'o':spec->base = 8;break;case 'x':spec->flags |= SMALL;case 'X':spec->base = 16;break;case 'd':case 'i':spec->flags |= SIGN;case 'u':break;default:spec->type = FORMAT_TYPE_INVALID;return fmt - start;}if (spec->qualifier == 'L')spec->type = FORMAT_TYPE_LONG_LONG;else if (spec->qualifier == 'l') {if (spec->flags & SIGN)spec->type = FORMAT_TYPE_LONG;elsespec->type = FORMAT_TYPE_ULONG;} else if (spec->qualifier == 'Z' || spec->qualifier == 'z') {spec->type = FORMAT_TYPE_SIZE_T;} else if (spec->qualifier == 't') {spec->type = FORMAT_TYPE_PTRDIFF;} else if (spec->qualifier == 'h') {if (spec->flags & SIGN)spec->type = FORMAT_TYPE_SHORT;elsespec->type = FORMAT_TYPE_USHORT;} else {if (spec->flags & SIGN)spec->type = FORMAT_TYPE_INT;elsespec->type = FORMAT_TYPE_UINT;}return ++fmt - start;}