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Re: [Gnu-arch-users] Re: give us a hand with arch

From: Robin Farine
Subject: Re: [Gnu-arch-users] Re: give us a hand with arch
Date: 29 Sep 2003 23:40:58 +0200
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2

>>>>> "Florian" == Florian Weimer <address@hidden> writes:


    Florian> The last block of a file contains data after the actual
    Florian> end of the file (back then, ReiserFS didn't optimize
    Florian> these cases). This data is also present in the page
    Florian> cache. You won't see it normally, because you cannot
    Florian> read() beyond the end of the file, but mmap() can only
    Florian> map complete pages, so you suddenly see the data (and it
    Florian> was random data from kernel or user space, typically not
    Florian> something which ever was on disk).

Ah yes, this is somewhat similar to the case of malloc'ed memory, it
would be an application bug to read/write past the end of the file,
but without disastrous effect on the kernel.

So I hope I understand your point better now, you cited an example
where Hans Reiser preferred optimization to correctness, source of
your prejudice.

I am not absolutely sure about this but I think that a POSIX kernel
should raise a SIGBUS when an application attempts an access between
the end of the file and the last page boundary. This would justify the


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