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Re: [Gnu-arch-users] Re: give us a hand with arch
From: |
Momchil Velikov |
Subject: |
Re: [Gnu-arch-users] Re: give us a hand with arch |
Date: |
30 Sep 2003 10:09:10 +0300 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50 |
>>>>> "Robin" == Robin Farine <address@hidden> writes:
>>>>> "Florian" == Florian Weimer <address@hidden> writes:
Robin> [...]
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).
Robin> So I hope I understand your point better now, you cited an example
Robin> where Hans Reiser preferred optimization to correctness, source of
Robin> your prejudice.
Robin> I am not absolutely sure about this but I think that a POSIX kernel
Robin> should raise a SIGBUS when an application attempts an access between
Robin> the end of the file and the last page boundary. This would justify the
Robin> optimization.
Hardware protection works with certain granularity. You can't
provide sub-page protection/smaller pages. (And you really do not want
to, TLB cache is already scarse enough).
However
"The system shall always zero-fill any partial page at the end
of an object. "
-- IEEE Std 1003.1-2001
So, this "optimization" is also a blatant violation of the standard
(if we assume reiser claims to be a POSIX system).
~velco
- Re: [Gnu-arch-users] Re: give us a hand with arch, (continued)
- Re: [Gnu-arch-users] Re: give us a hand with arch, Andrew Suffield, 2003/09/29
- [OT] psychofs (was: [Gnu-arch-users] Re: give us a hand with arch), Robin Farine, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, David Brown, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, Andrew Suffield, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, Stephen J. Turnbull, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, Charles Duffy, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, Florian Weimer, 2003/09/30
- Re: [Gnu-arch-users] Re: give us a hand with arch, Bruce Stephens, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch [reiserfs-bashing], Charles Duffy, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch [reiserfs-bashing], Miles Bader, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch,
Momchil Velikov <=
- Re: [Gnu-arch-users] Re: give us a hand with arch, Adam Spiers, 2003/09/29
- Re: [Gnu-arch-users] Re: give us a hand with arch, Tom Lord, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Momchil Velikov, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Tom Lord, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Andrew Suffield, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Dustin Sallings, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Tom Lord, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, David Brown, 2003/09/27
- Re: [Gnu-arch-users] Re: give us a hand with arch, Florian Weimer, 2003/09/28
- [Gnu-arch-users] Re: give us a hand with arch, Pau Aliagas, 2003/09/28