Date: Fri, 16 Jun 2000 12:49:17 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Joy Ganguly <joy@niksun.com> Cc: freebsd-hackers <freebsd-hackers@FreeBSD.ORG> Subject: Re: mmap and file writes...??? Message-ID: <200006161949.MAA60866@apollo.backplane.com> References: <394A3727.1FEC441E@falcon.niksun.com>
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:hi all, : :i have a question regarding mmap and file write. a file is mmap'ed and :data is written into the mapped region. now the same region is written. :(as shown below) : :buf = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); :. :. /* some data put in buf */ :. : :write(fd, buf, len); : : :now does this lead to unnecessary copies?? more specifically what :happens if two virtual addresses point to the same physical address and :data is copied from one to the other. : :thanx in advance : :joy You can copy data from one part of a file to another using this method, but only if the two areas do not overlap. If the areas overlap, the result will be possible corruption of the file. -Matt Matthew Dillon <dillon@backplane.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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