subprocess opens stdin to /dev/null incorrectly

[jsternberg]

After forking a new process, stdin in the child process is closed and re-opened to /dev/null. It's opened with the flag O_WRONLY. It should be opened with O_RDONLY. For example, if the below program is used within ninja, it will print -1.

#include <stdio.h>
#include <unistd.h>

int main() {
    int fd = fileno(stdin);
    char buf[4096];
    ssize_t bytes_read = read(fd, buf, 4096);
    printf("%ld\n", bytes_read);
    return 0;
}

If you do this in bash, it will print 0.

$ ./a.out < /dev/null

Ninja should probably do the same unless there's a particular reason why it opens stdin incorrectly (in which you could just save time by closing stdin and not opening /dev/null.

[evmar]

Thanks for the detailed report and diagnosis!