Re: Rereading A Partition Table

• Subject: Re: Rereading A Partition Table
• From: Dan Markarian <email@hidden>
• Date: Thu, 16 Aug 2007 12:20:05 -0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Hey Duane,

Dan

On 16 Aug 2007, at 11:38 AM, Duane Murphy wrote:

--- At Thu, 16 Aug 2007 10:53:50 -0400, Dan Markarian wrote:

Hey Duane,

We do not detect live changes to a partition map in Tiger.

Thanks. Then I am back to my original question. When Disk Utility
(diskutil) partitions a drive it takes it off-line then puts it back on-
line. Clearly this causes everything to be re-read.

I'd like to do the same thing. Disk Arbitration doesn't seem quite the
right tool for doing this. In fact even Disk Utility does not fully
"eject" a firewire disk unless it is partitioning.

I surely don't want to request the user to restart just to re-read
changes to a disk.

Is there somewhere I should look for how to do this? Another mailing list?

Thanks for the help.

On 15 Aug 2007, at 9:58 PM, Duane Murphy wrote:

--- At Wed, 15 Aug 2007 17:26:42 -0700, Chris Sarcone wrote:

Duane --

I'm making changes to GUID partition disks partition table, and I
would
like the system to re-read the disk in order to recognize new
partitions
on the disk.

What do I need to do to get the system to re-read the disk and
recognize
the changes?

I've tried several disk util commands (unmountDisk, mountDisk, and
eject) but they don't re-read the disk.

Disk Utility->Eject does the same thing (ie nothing).

I note that this is a FireWire drive, but it could also be an
internal
drive or any other non-network drive.

For example, when Disk Utility partitions a disk, it fully unmounts
and
then remounts the disk. How can I do the same thing?

Try opening and closing the raw disk node for the whole device.

Hi Chris,
That's what I was told. In fact, I am editing the partition table
using /
dev/rdisk1
(or whatever number). But when it is closed it doesn't do anything.

Here's how I open. inDisk is "/dev/rdisk1" (for example);
	int diskDescriptor
		= open( inDisk, O_RDWR | O_SHLOCK, S_IRUSR | S_IWUSR | S_IRGRP );

later I just

close( diskDescriptor );

There's no errors and in fact, the disk is nicely edited. If I unplug
the drive and plug it back in the partitions looks exactly like what I
want, but it's hard to do that for internal disks. :-)

...Duane

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