Re: HFS and extents (was: no subject)
Re: HFS and extents (was: no subject)
- Subject: Re: HFS and extents (was: no subject)
- From: Michael Smith <email@hidden>
- Date: Mon, 15 Jan 2007 13:01:41 -0800
According to a Wikipedia page about extents, it has stated HFS+ is
among several filesystems that support extents.
What do you mean by "support extents"?
HFS uses extent-based allocation; that is, rather than enumerating
every block that makes up an allocation, allocations are recorded as
a starting block and a run length.
However, since this is simply a means of tracking allocations, it's
probably not what you're thinking of.
All the documentation
I've seen about user level extent support in Mac OS X, as far as "any
documentation" goes, is the Xsan programming guide (specifically, the
F_ALLOCEXTSPACE fcntl flag.)
Does F_ALLOCEXTSPACE work on HFS+, non-Xsan volumes? If not, what is
the HFS+ generic equivalent?
I don't think that F_ALLOCEXTSPACE does what you think it does, but
if all you mean is that you want a single contiguous slab of disk
space at an offset within a file, you want F_PREALLOCATE which is
documented in fcntl(2).
= Mike
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