From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: First cut at git port to Cygwin
Date: Mon, 10 Oct 2005 12:26:16 -0700
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References: <20051005155457.GA30303@trixie.casa.cgf.cx> <20051005191741.GA25493@steel.home> <20051005202947.GA6184@trixie.casa.cgf.cx> <81b0412b0510060205v4cd510c9wb4b06a3ed9242c8@mail.gmail.com> <81b0412b0510060307q431b64edt4196553bce28346c@mail.gmail.com> <81b0412b0510070544v3e7cf0b4n521db8ff7e4e335a@mail.gmail.com> <Pine.LNX.4.64.0510070828270.31407@g5.osdl.org> <20051007205450.GA14827@steel.home> <20051007212250.GA1423@steel.home> <4346E8AC.5030503@citi.umich.edu> <20051007213952.GA8821@steel.home> <Pine.LNX.4.64.0510080900510.31407@g5.osdl.org> <Pine.LNX.4.63.0510082023130.25971@wbgn013.biozentrum.uni-wuerzburg.de> <7vr7avrgr2.fsf@assigned-by-dhcp.cox.net> <434AB663.8050205@zytor.com> <Pine.LNX.4.63.0510102100010.7688@wbgn013.biozentrum.uni-wuerzburg.de>
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Cc: Junio C Hamano <junkio@cox.net>, git@vger.kernel.org,
	Linus Torvalds <torvalds@osdl.org>
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To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
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Johannes Schindelin wrote:
> 
>>Junio C Hamano wrote:
>>
>>>PROT_WRITE is true, but we do MAP_PRIVATE, and if I recall
>>>correctly we do not write file via mmap -- at least we do not
>>>intend to.
>>>
>>
>>Then PROT_READ probably makes more sense?
> 
> Not necessarily. Sometimes you need to annotate the data from the index, 
> and this does not need to be written back to the index file.
> 

In the above sentence, emphasis on "at least we do not intend to."  If 
writes are done legitimately then that's fine, but we shouldn't have 
"accidental writes" -- those would be program bugs!

> 
>>>Yes.  It might have been overkill that you supported writing
>>>changes back, though.
>>
>>Not just overkill; if we do MAP_PRIVATE it's actively WRONG.
> 
> See above.
> 

Eh?  If we MAP_PRIVATE, *and* we (intentionally) write to it, we 
*BETTER* not write anything back.

	-hpa