3rd argument to open

Hal Murray hmurray at megapathdsl.net
Mon Nov 13 04:03:19 UTC 2017

My Linux man page says open(2) takes an optional 3rd argument - the mode bits 
that are used if the file is created.  The POSIX man pages don't say anything 
about it, but do leave a ... in the skeleton for open.

        The mode argument specifies the file mode bits be applied when a
        new file is  created.   This  argument  must  be  supplied  when
        O_CREAT  or  O_TMPFILE is specified in flags; if neither O_CREAT
        nor O_TMPFILE is specified, then mode is ignored.

Is that interesting for refclocks?  Is there any case where things like 
/dev/tty6 get created when opened?  If not, any reason I shouldn't remove the 
3rd argument?  (I'm interested in refclocks, not log files and such which 
actually might get created.)

If there is a good use for it, is 0777 ever the right value?


                    up->ppsapi_fd = open(peer->cfg.ppspath,
                        O_RDWR | O_NOCTTY | O_NONBLOCK, S_IRUSR | S_IWUSR);

        up->fddev = open(peer->cfg.ppspath ? peer->cfg.ppspath : device,
                             O_RDWR, 0777);

        fd = open(dev, O_RDWR | O_NONBLOCK | O_NOCTTY, 0777);

These are my opinions.  I hate spam.

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