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/* We can be called as hotplug helper */
/* Kernel cannot provide suitable stdio fds for us, do it ourself */
bb_sanitize_stdio();
void FAST_FUNC bb_sanitize_stdio(void)
{
bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
}
enum {
DAEMON_CHDIR_ROOT = 1,
DAEMON_DEVNULL_STDIO = 2,
DAEMON_CLOSE_EXTRA_FDS = 4,
DAEMON_ONLY_SANITIZE = 8, /* internal use */
};
void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
{
int fd;
if (flags & DAEMON_CHDIR_ROOT)
xchdir("/"); //切换到根目录，如果切换失败，那么进入die状态
if (flags & DAEMON_DEVNULL_STDIO) { //是否使用DEVNULL设备作为输入输出设备
close(0); //文件描述符0，标准输入，缺省是键盘
close(1); //文件描述符1，标准输出，缺省是屏幕
close(2); //文件描述符2，错误输出，缺省是屏幕
}
fd = open(bb_dev_null, O_RDWR); //bb_dev_null为"/dev/null"
if (fd < 0) {
/* NB: we can be called as bb_sanitize_stdio() from init
* or mdev, and there /dev/null may legitimately not (yet) exist!
* Do not use xopen above, but obtain _ANY_ open descriptor,
* even bogus one as below. */
fd = xopen("/", O_RDONLY); /* don't believe this can fail */
}
while ((unsigned)fd < 2)
fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
if (!(flags & DAEMON_ONLY_SANITIZE)) {
if (fork_or_rexec(argv))
exit(EXIT_SUCCESS); /* parent */
/* if daemonizing, make sure we detach from stdio & ctty */
setsid();
dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
}
while (fd > 2) {
close(fd--);
if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
return;
/* else close everything after fd#2 */
}
}
./include/libbb.h:extern const char bb_dev_null[];
./libbb/messages.c:const char bb_dev_null[] ALIGN1 = "/dev/null";
// Die if we can't chdir to a new path.
void FAST_FUNC xchdir(const char *path)
{
if (chdir(path)) //切换到path目录。如果失败，那么进入die状态。
bb_perror_msg_and_die("chdir(%s)", path);
}
void FAST_FUNC bb_perror_msg_and_die(const char *s, ...)
{
va_list p;
va_start(p, s);
/* Guard against ": Success" */
bb_verror_msg(s, p, errno ? strerror(errno) : NULL); //如果系统出错，那么errno将是非0，strerror(errno)将把错误代码转换成字符串信息
va_end(p);
xfunc_die();
}
void FAST_FUNC bb_verror_msg(const char *s, va_list p, const char* strerr)
{
char *msg, *msg1;
int applet_len, strerr_len, msgeol_len, used;
if (!logmode)
return;
if (!s) /* nomsg[_and_die] uses NULL fmt */
s = ""; /* some libc don't like printf(NULL) */
used = vasprintf(&msg, s, p); //字符串格式化
if (used < 0)
return;
/* This is ugly and costs +60 bytes compared to multiple
* fprintf's, but is guaranteed to do a single write.
* This is needed for e.g. httpd logging, when multiple
* children can produce log messages simultaneously. */
applet_len = strlen(applet_name) + 2; /* "applet: " */
strerr_len = strerr ? strlen(strerr) : 0;
msgeol_len = strlen(msg_eol);
/* can't use xrealloc: it calls error_msg on failure,
* that may result in a recursion */
/* +3 is for ": " before strerr and for terminating NUL */
msg1 = realloc(msg, applet_len + used + strerr_len + msgeol_len + 3); //重新分配内存
if (!msg1) {
msg[used++] = '\n'; /* overwrites NUL */
applet_len = 0;
} else {
msg = msg1;
/* TODO: maybe use writev instead of memmoving? Need full_writev? */
memmove(msg + applet_len, msg, used);
used += applet_len;
strcpy(msg, applet_name);
msg[applet_len - 2] = ':';
msg[applet_len - 1] = ' ';
if (strerr) {
if (s[0]) { /* not perror_nomsg? */
msg[used++] = ':';
msg[used++] = ' ';
}
strcpy(&msg[used], strerr);
used += strerr_len;
}
strcpy(&msg[used], msg_eol);
used += msgeol_len;
}
//
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