wifi6 Linux driver - Intel ax201 wifi driver - 5 - Linux kernel

struct_size

這個是 Linux kernel 4.18 之後才有的, 定義在 linux/overflow.h

--
程式:

cmd.len[0] = struct_size(pattern_cmd, patterns, wowlan->n_patterns);

pattern_cmd = kmalloc(cmd.len[0], GFP_KERNEL);

--
這用法是在於 pattern_cmd 是一個 structure pointer.

struct iwl_wowlan_patterns_cmd_v1 *pattern_cmd;

structure 很單純, 就是有多少個 patterns: n_patterns 和 pattern pointer array
struct iwl_wowlan_patterns_cmd_v1 {
__le32 n_patterns;
struct iwl_wowlan_pattern_v1 patterns[];
} __packed; /* WOWLAN_PATTERN_ARRAY_API_S_VER_1 */

--

計算方法:

就是: (wowlan->n_patterns) * (*pattern_cmd->patterns) + sizeof(*pattern_cmd)

PS: C 運算子 -> 優先於 *

運算子優先權 (C 語言)
Percedence Table

	運算子 Operator	說 明 Description	結合順序 Associativity
1	() [] -> . ++ --	Function call Array subscripting Element selection (of struct or union) through pointer Element selection (of struct or union) by reference increment/decrement (suffix) (註1)	左至右
2	! ~ ++ -- + - * & (type) sizeof	logic NOT bitwise NOT increment/decrement (prefix) unary plus and minus Indirection (dereference, right value) Address-of (left value) type cast Size-of	右至左
3	* / %	Arithmetic multiplication, division, and remainder	左至右
4	+ -	Arithmetic addition, subtraction	左至右
5	<< >>	Bitwise left shift, right shift	左至右
6	< <= > >=	Relational less than, not greater than Relational greater than, not less than	左至右
7	== !=	Relational equal, not equal	左至右
8	&	Bitwise AND	左至右
9	^	Bitwise XOR	左至右
10	|	Bitwise OR	左至右
11	&&	Logical AND	左至右
12	||	Logical OR	左至右
13	?:	Ternary conditional	右至左
14	= += -= *= /= %= &= ^= |= <<= >>=	Direct assignment Assignment by sum, difference Assignment by product, quotient, remainder Assignment by bitwise AND, XOR, OR Assignment by bitwise left shift, right shift	右至左
15	,	Comma	左至右

註1: 這一條和 K&R C 書上所列不同, 這是 K&R C 原版的錯誤. 目前所有的 C/C++ 編譯器都還保留這個錯誤, 並且不會被修正. 請參考 Wiki: C (programming language) Syntax 的第 5 小段 (標題 "Character Set" 的前面小段). 或者 K&R 原版 第 3 頁. 摘錄如下:
"C, like any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better."