Date: Wed, 10 Feb 1999 18:39:49 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: tlambert@primenet.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG Subject: Re: portability of shm, mmap, pipes and socket IPC Message-ID: <199902101839.LAA18447@usr07.primenet.com> In-Reply-To: <199902092310.PAA61722@apollo.backplane.com> from "Matthew Dillon" at Feb 9, 99 03:10:52 pm
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> :FreeBSD has a unified vm and buffer cache. In theory, you do not > : need to call msync(2), ever, on such a system. However, > : there are a number of coherency bugs that make it necessary > : to call it (mostly in INN-type situations, where the file is > : being extended while it is mapped). > > What coherency bugs? As far as I know, extending a mmap()'d file > works just fine. You cannot *write* into the mmap()'d area beyond > the end of a file until you ftruncate() the file larger, but that is > true on all implementations that I know of. It is also appropriate - > the validity of the mmap()'d data only extends to the logical end of > file. Yes, yes, that's not the problem. The problem is that INN apparently still fails when using mmap without msync. The utility of msync is overrated; the code does not actually do what the manual page claims it does, in any case. > :FreeBSD semaphores are inadequately resource tracked in _exit(). > > All semaphores are inadequately resource tracked in _exit(), it's a > problem inherited from the SYSV implementation. Shared memory is badly tracked. But semaphores are supposed to be capable of being counted out by _exit(), per the SysV man pages for semop(2) an exit(2): http://www.freebsd.org/cgi/man.cgi?query=semop&sektion=2&apropos=0&manpath=SunOS+5.5.1 http://www.freebsd.org/cgi/man.cgi?query=exit&sektion=2&apropos=0&manpath=SunOS+5.5.1 FreeBSD either doesn't do this, or the FreeBSD manual pages are in error. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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