Subject: Re: SCSI MMC device abstraction and UDF patch for review
To: YAMAMOTO Takashi <>
From: Bill Studenmund <>
List: tech-kern
Date: 12/28/2005 13:33:34
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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:
> > >
> >=20
> > - 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
that experience.

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
same changes.

Take care,


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