Re: [PATCH] xfstests 255: add a seek_data/seek_hole tester

Marco Stornelli
2011-08-27T08:36:41Z

Il 26/08/2011 16:41, Zach Brown ha scritto:
>>> Hole: a range of the file that contains no data or is made up
>>> entirely of NULL (zero) data. Holes include preallocated ranges of
>>> files that have not had actual data written to them.
>
>> No for me. A hole is made up of zero data? It's a strange definition
>> for me.
>
> It's a very natural definition for me. It mirrors the behaviour of
> read() of sparse data inside i_size that file system authors already
> have to consider.
>
> It's also a reminder for people that this interface is about avoiding
> reading zeros. Systems that track contents can do this for files that
> had tons of zeros written. The data is there but the app is
> specifically asking us to skip it by using SEEK_DATA.
>
> - z
>

I think we need to consider a hole and "data not present/not written
yet" as two different cases even they are related. For example, if I do
an fallocate without keep size option, then I do a read, I have the same
behavior of sparse data inside i_size, but the blocks are allocated so
no sparse data in this case. Simply there are no difference from app
point of view.

Marco