Date: Wed, 13 Mar 2002 01:04:53 -0800 From: Farooq Mela <fmela0@sm.socccd.cc.ca.us> To: Alfred Perlstein <bright@mu.org> Cc: freebsd-hackers@freebsd.org, tlambert2@mindspring.com Subject: Re: Recv() to a mmap'ed file? Message-ID: <3C8F1635.B6E3FA5A@sm.socccd.cc.ca.us> References: <3C8E6CD5.67F23CF2@sm.socccd.cc.ca.us> <20020312214851.GK92565@elvis.mu.org> <3C8EEA50.C3E17315@sm.socccd.cc.ca.us> <20020313060553.GF32410@elvis.mu.org>
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Hi,
WRT to Terry's email, I initialized the file by writing N nul ('\0')
bytes to it.
Alfred Perlstein wrote:
> Have you tried the mapping with PROT_READ as well? I don't think
> most arches allow for access without PROT_READ along with PROT_WRITE.
Oops.. and I even read the thread a little while ago about PROT_WRITE
alone not working on x86, but working on alpha because write-only
pages are supported on that architecture.. silly me
anyhow, I changed it to use O_RDWR instead of O_WRONLY to open(2) and
then I used both PROT_READ and PROT_WRITE as the protection argument,
and then the file transfer worked like a charm.
Which brings us to the question, on x86 arch why do we even allow a
PROT_WRITE only map to be created? It is useless and a program which
gets a write-only map will think it actually has such a mmap'ed
region, but it will get a SIGBUS if it tries to write to it. It would
be better to return -1 and set errno to EFAULT than to have this brain
damage imho.
--
Farooq
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