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cunixposixsystem-callsxv6

What's the easiest workaround on the OS, which doesn't have the dup2 syscall?

I'm working with the xv6 OS and I need to substitute stdio with a file. This is normally done with the dup2 syscall, which this OS doesn't have. Is there any workaround? Do I have to implement my own syscall which will try to mimic the POSIX's one behavior? Or can the functionality I need (substitute the file descriptor) can be implemented in a regular function in a c program? Thanks.

Solution 
  • dup2( filedes, filedes2 );

    means

    close( filedes2 );
fcntl( filedes, F_DUPFD, filedes2 );

    You can do

    close(0);
dup(fd);

    subject to race conditions, since dup2 atomic function but close and dup include two function calls.