Subject: Re: SCSI MMC device abstraction and UDF patch for review
To: YAMAMOTO Takashi <firstname.lastname@example.org>
From: Bill Studenmund <email@example.com>
Date: 12/28/2005 13:33:34
Content-Type: text/plain; charset=us-ascii
On Sat, Dec 24, 2005 at 02:41:54PM +0100, Reinoud Zandijk wrote:
> Hiya Takashi,
> On Sat, Dec 24, 2005 at 08:35:22PM +0900, YAMAMOTO Takashi wrote:
> > > ftp://ftp.NetBSD.org/pub/NetBSD/misc/reinoud/src-diffs-udf.20051222.gz
> > - it seems to do double-caching. ie. at both of udf and block device.
> > is it intended?
> Yes and no. For UDF it is better to use caching in udf since blocks can=
> move around esp. on recordables; every disc write changes the location of=
> the block so its easier to have it cached on the file's vnode on its=20
> logical block instead of a moving buffer on disc. Setting B_NOCACHE in th=
> buffers passed to the block device is prolly advisable yes.
Why is it easier?
UDF is not the first file system in our kernel to face this issue. LFS has=
been dealing with it for over a decade. I think it would be VERY advisable=
for UDF to do the exact same thing for a number of reasons:
1) LFS has worked out a huge number of the issues, so UDF can gain from=20
2) It will be much easier for others to maintain the code if we only have=
one way that we cope with block-shuffling file systems.
3) If UDF shows us we really need to fix an issue, LFS may gain from the=20
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