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Re: RFC: SEEK_DATA/SEEK_HOLE implementation version 2


On Mon, Oct 03, 2011 at 04:54:29AM +0000, YAMAMOTO Takashi wrote:
> > The new implementation presents the default one-blob for file systems that
> > don't implement it. For NetBSD its currently implemented for UFS and is
> > tested for FFS with/without WAPBL, ext2fs and lfs. It is present in our
> > ZFS import but aparently disabled still and i dont have a ZFS partition to
> > play with. I might be tempted to try it later on my scratch machine :) UDF
> > is next but shouldn't be that difficult.
> why is the VOP_FSYNC call necessary?

The sparse region search code depends on the indirect blocks being correctly
written out as it traverses them. If the file is still `dirty' all the
indirect blocks are present as negative indices so the normal FFS code works
but their indirect blocks, when addressed with their disc addresses, are not

The FFS sparse region search code depends on the indirect blocks to see where
actual data is recorded and needs the indirect blocks to be up-to-date. A
range sync with only the negative range might also suffice but since most if
not all of the applications of this code is dealing with backup/processing the
VOP_FSYNC() is normally a NOP.

I hope this explanation helps :)

With regards,

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