linux-kernel - ssi_code在signalfd_siginfo结构中有什么用？

Question

我正在使用 signalfd() 来监视我的进程创建的子进程的死亡。如果我用信号杀死一个子进程，父进程会在信号 fd 上获得一个读取事件，并填充了 signalfd_siginfo 结构。它有一个字段 ssi_code ，该字段设置为 child 收到的信号编号(例如，如果我向 child 发送了 SIGKILL，则为 9)。

我可以一直依赖这种行为吗？支持 signalfd 的所有 Linux 内核版本对该字段的用法都相同吗？

注意:如果子进程调用 exit()，则传递给 exit 的代码会填充到 ssi_code 中。

Answer 1

signalfd 的手册页指出:

The format of the signalfd_siginfo structure(s) returned by read(2)s from a signalfd file descriptor is as follows:

           struct signalfd_siginfo {
               uint32_t ssi_signo;   /* Signal number */
               int32_t  ssi_errno;   /* Error number (unused) */
               int32_t  ssi_code;    /* Signal code */
               uint32_t ssi_pid;     /* PID of sender */
               uint32_t ssi_uid;     /* Real UID of sender */
               int32_t  ssi_fd;      /* File descriptor (SIGIO) */
               uint32_t ssi_tid;     /* Kernel timer ID (POSIX timers)
               uint32_t ssi_band;    /* Band event (SIGIO) */
               uint32_t ssi_overrun; /* POSIX timer overrun count */
               uint32_t ssi_trapno;  /* Trap number that caused signal */
               int32_t  ssi_status;  /* Exit status or signal (SIGCHLD) */
               int32_t  ssi_int;     /* Integer sent by sigqueue(2) */
               uint64_t ssi_ptr;     /* Pointer sent by sigqueue(2) */
               uint64_t ssi_utime;   /* User CPU time consumed (SIGCHLD) */
               uint64_t ssi_stime;   /* System CPU time consumed (SIGCHLD) */
               uint64_t ssi_addr;    /* Address that generated signal
                                        (for hardware-generated signals) */
               uint8_t  pad[X];      /* Pad size to 128 bytes (allow for
                                         additional fields in the future) */
           };

似乎很清楚: ssi_signo 包含信号编号。它说 ssi_code :

Not all fields in the returned signalfd_siginfo structure will be valid for a specific signal; the set of valid fields can be determined from the value returned in the ssi_code field. This field is the analog of the siginfo_t si_code field; see sigaction(2) for details.

见 sigaction man有关此代码的更多详细信息，请访问 不是 信号编号。