Date: Sat, 8 Jul 1995 14:39:07 +1000 From: Bruce Evans <bde@zeta.org.au> To: freebsd-current@freebsd.org Subject: Re: /etc/rc and "rm -f /var/spool/lock/*" Message-ID: <199507080439.OAA14323@godzilla.zeta.org.au>
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>> |Lock files suck. They should not be used at all, and the only client >> |that really needs them right now is mgetty. >> >> What if you wanted to run outgoing hylafax and outgoing >> 'ppp -auto' on the same port. >Open the callout device with O_EXCL. Erm, O_EXCL is useless for locking devices in FreeBSD. POSIX specifies the behaviour for open() with both O_CREAT and O_EXCL set. This behaviour is useless for locking of devices (it only works of the file doesn't already exist, and non-existent files aren't devices). The behaviour is implementation-defined if only O_EXCL is set. In FreeBSD, the behaviour is to ignore O_EXCL. FreeBSD provides the TIOCEXCL ioctl. This is not so good in theory (open() + ioctl() isn't atomic, so the locking can at best be advisory) and is worse in practice (the ioctl always succeeds and no advise is given about prior locking; also, the locking doesn't apply to root). Bruce
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