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

[Marco Stornelli]

Il 27/08/2011 10:30, Marco Stornelli ha scritto:
> 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

Please don't care about the last part, when reading in this case the app 
will have a return value different from zero obviously, I was under the 
effect of a beer :) However I'd add to the definition, that we consider 
holes only inside i_size, as Zack said. In this way, we haven't got any 
ambiguity for preallocated space beyond eof.

Marco
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