[hackers] [scroll] handle child exit via POLLHUP instead of sigchld || Jan Klemkow

[git]

commit 97b90414891e957c95caffe078c69b18aa38e659
Author:     Jan Klemkow <j.klem...@wemelug.de>
AuthorDate: Fri Apr 17 21:46:55 2020 +0200
Commit:     Jan Klemkow <j.klem...@wemelug.de>
CommitDate: Fri Apr 17 21:46:55 2020 +0200

    handle child exit via POLLHUP instead of sigchld
    
    this fix a racecondition which leads to wrong return code.

diff --git a/scroll.c b/scroll.c
index 3952a54..3219915 100644
--- a/scroll.c
+++ b/scroll.c
@@ -89,19 +89,6 @@ die(const char *fmt, ...)
        exit(EXIT_FAILURE);
 }
 
-void
-sigchld(int sig)
-{
-       pid_t pid;
-       int status;
-
-       assert(sig == SIGCHLD);
-
-       while ((pid = waitpid(-1, &status, WNOHANG)) > 0)
-               if (pid == child)
-                       exit(WEXITSTATUS(status));
-}
-
 void
 sigwinch(int sig)
 {
@@ -421,8 +408,6 @@ main(int argc, char *argv[])
        if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) < 0)
                die("ioctl:");
 
-       if (signal(SIGCHLD, sigchld) == SIG_ERR)
-               die("signal:");
        if (signal(SIGWINCH, sigwinch) == SIG_ERR)
                die("signal:");
 
@@ -553,11 +538,9 @@ main(int argc, char *argv[])
        if (close(mfd) == -1)
                die("close:");
 
-       pid_t pid;
        int status;
-       while ((pid = waitpid(-1, &status, WNOHANG)) > 0)
-               if (pid != child)
-                       continue;
+       if (waitpid(child, &status, 0) == -1)
+               die("waitpid:");
 
        return WEXITSTATUS(status);
 }