Re: How does ext2 implement sparse files?

[Lars Noschinski]

[Sorry for using an invalid mail address in my previous post]

* Andi Kleen <andi@xxxxxxxxxxxxxx> [08-02-01 10:28]:
> Lars Noschinski <lklml@xxxxxxxxxxxxxxxx> writes:
>
> > For an university project, we had to write a toy filesystem (ext2-like),
> > for which I would like to implement sparse file support. For this, I
> > digged through the ext2 source code; but I could not find the point,
> > where ext2 detects holes.
> >
> > As far as I can see from fs/buffer.c, an hole is a buffer_head which is
> > not mapped, but uptodate. But I cannot find a relevant source line,
> > where ext2 makes usage of this information.
>
> It does not explicitely detect holes; holey data is just never written
> so no space for it is allocated.

Thanks for the answers. No that I know that, it is kind of obvious. I
was irritated yesterday by a bug a bug in our implementation (number of
used blocks is reported as filesize/blocksize); so I was expecting the
VFS to issue write requests for empty pages (which would be sillly, I
know).

Thanks,
    Lars.
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