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From: joeb@hpmwtd.HP.COM (Joe Ballantyne)
Newsgroups: comp.sys.mac.programmer
Subject: File Manager questions
Message-ID: <1050001@hpmwjcb.HP.COM>
Date: 16 Mar 89 23:54:02 GMT
Organization: HP Microwave Tech. - Santa Rosa, Ca.
Lines: 58




I am writing an application that creates some very
large contiguous files using File Manager routines.
I want to be sure that the files are always contiguous
even when they are copied by the Finder from one disk
to another. 

Will the Finder always copy a contiguous file as a 
contiguous file?

Is it possible to force the Finder to keep a file
a contiguous file?  If so, how is this done?

I had the brilliant? idea that if I set the file clump
size of my contiguous file to the size of the file
itself, then perhaps the finder would use the original
file's clump size when allocating space on the
disk for the copy.  Is that true?
(I'm beginning to have my doubts.)

Unfortunately, I have found it impossible (so far) to
even set the file clump size.  I first tried using 
PBSetCatInfo. I set the file clump size feild
to the value that I wanted, called PBSetCatInfo, recalled
PBGetCatInfo, and the clump size had been conveniently
set to zero for me.

I then decided that Pascal wouldn't do it for me, so I tried
machine language.  I found the files file control block, set
the clump size long word directly in the file control block,
set the dirty bit (bit 15) of the ioflags word, set the file 
has its own clump size bit (bit 6) of the ioflags word, jumped
back to my program, (everything seemingly ok) called flushvol,
and naturally, the system crashed.  

Is it possible to set a file's clump size to something other
than zero?

If I didn't set bit 15 in my assembly language subroutine, 
the flushvol and subsequent file manager
calls worked fine, BUT when I checked the file clump size with
FEdit Plus, it was zero.  

Do I need to set bit 7 of the ioflags word?

How does one set the clump size of a file in a permanant
manner?  Do you have to access the B* trees directly?

Thanks in advance for your help

Joe Ballantyne
Hewlett Packard
Microwave Technology Division
Santa Rosa, CA 95405

joeb@hpmwjcb.HP.COM