Re: Ejecting An Image Disk
Re: Ejecting An Image Disk
- Subject: Re: Ejecting An Image Disk
- From: Luther Fuller <email@hidden>
- Date: Fri, 31 Oct 2008 12:31:01 -0500
On Oct 31, 2008, at 11:53 AM, Axel Luttgens wrote:
Let's first consider the problem of hditutil -imageinfo applied to a
disk image having at least one mounted volume.
If that volume is R/W, items on that volume are liable to be changed/
created/deleted at any time from other parts of the system; this
means that the disk image itself is liable to be continuously
modified.
hditutil thus needs to somehow freeze the disk image for a short
time, so as to extract the needed info, a *consistent* info, from
the disk image.
If you experiment with the -debug flag, you'll notice that hdiutil
resolves that problem by attempting to acquire a lock on the disk
image.
This will always be successful when the disk image is R/O.
But this will (almost) always fail when the disk image is R/W.
That sounds reasonable. Confirmed recently by an experiment. The Size
info could change.
But all I need is the encrypted status.
The reason here seems to be that the "meta-data" itself is encrypted
(just do an hexdump on an unencrypted disk image, and compare to
what comes with an encrypted one).
From the point of view of security, this seems to be reasonable: it
would otherwise be possible to directly tamper with the disk image,
without having the fact noticed by the legitimate owner of that disk
image.
But of course, the password is then needed to fetch even the "meta-
data".
I agree ... but it's still illogical.
The scripts I am working on need to determine if a disk image file is
encrypted so it can inform the user that it doesn't handle (burn,
convert, &c.) encrypted files. Ever. No passwords needed. Doing that
ought to be simple ... but it's not.
Perhaps hdiutil's imageinfo verb should have a '-encrypted' option
that ALWAYS returns ONLY the encryption status. This would solve my
problem.
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