Re: How does ext2 implement sparse files?

[Andi Kleen]

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.

-Andi
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