Date: Sun, 4 Feb 1996 23:18:18 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: j@uriah.heep.sax.de (J Wunsch) Cc: freebsd-hackers@freebsd.org Subject: Re: FAT filesystem performance Message-ID: <199602042218.XAA19281@labinfo.iet.unipi.it> In-Reply-To: <199602041822.TAA01613@uriah.heep.sax.de> from "J Wunsch" at Feb 4, 96 07:21:54 pm
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> As Luigi Rizzo wrote: > > > I am wondering: how hard would it be to add mmap() to, say, wd.c ? > > Would it have other useful applications ? > > This would only shift the problem from the msdosfs code into the > various device drivers. Well, let me first say that I don't know exactly how mmapping files works internally. But what I expect is to have the kernel do its best to keep blocks in core and write them back (if necessary) when the file is unmapped. Now assume for a moment the existence of a Very Simple File System (VSFS), which always contains a single file spanning the whole partition. mmapping the unique file of this VSFS should do exactly what I want, and the VSFS is device independant (it's a file system!). This VSFS is logically above the device driver, but it might just be a standard piece of the system which all device drivers invoke to implement mmap(). Does the above sound reasonable ? I have no idea on how complex would it be to implement this, but the feeling is that it is more of a design problem rather than a coding problem (for those who know how to write such code, of course :)) Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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