uclinux-2008R1-RC8(bf561)到VDSP5的移植（13）：未命名union的問題

在include/linux/shed.h中定義了一個結構體：

/*
* NOTE! "signal_struct" does not have it's own
* locking, because a shared signal_struct always
* implies a shared sighand_struct, so locking
* sighand_struct is always a proper superset of
* the locking of signal_struct.
*/
struct signal_struct {
…
/* job control IDs */
pid_t pgrp;
struct pid *tty_old_pgrp;

union {
pid_t session __deprecated;
pid_t __session;
};
…
};

在include/linux/init_task.h中定義了一個宏來對這個結構體進行初始化：

#define INIT_SIGNALS(sig) {                        /
     .count        = ATOMIC_INIT(1),                /
     .wait_chldexit     = __WAIT_QUEUE_HEAD_INITIALIZER(sig.wait_chldexit),/
     .shared_pending    = {                         /
         .list = LIST_HEAD_INIT(sig.shared_pending.list),   /
         .signal = {{0}}},                   /
     .posix_timers = LIST_HEAD_INIT(sig.posix_timers),      /
     .cpu_timers   = INIT_CPU_TIMERS(sig.cpu_timers),        /
     .rlim         = INIT_RLIMITS,                      /
     .pgrp         = 0,                        /
     .tty_old_pgrp   = NULL,                        /
     { .__session      = 0},                        /
}

在這裡

{ .__session　　　　　 = 0},　　/

會引發一個錯誤：

"../../arch/blackfin/kernel/init_task.c", line 38: cc0136: error: union
"<unnamed>" has no field "__session"
static struct signal_struct init_signals = INIT_SIGNALS(init_signals);

怎麼看都有__session這個成員啊，實際引發這個錯誤的原因是在結構體中使用了未命名的union。因此必須做如下修改：

struct signal_struct {
…
/* job control IDs */
pid_t pgrp;
struct pid *tty_old_pgrp;

union {
pid_t session __deprecated;
pid_t __session;
}signal_struct_session;
…
};

其實就是隨便給這個union定義一個變量。