Re: Difference between dvd and dmg
Re: Difference between dvd and dmg
- Subject: Re: Difference between dvd and dmg
- From: "Gerriet M. Denkmann" <email@hidden>
- Date: Wed, 12 Oct 2005 18:54:16 +0200
On 12.10.2005, at 18:08, John Stiles wrote:
Gerriet M. Denkmann wrote:
Because pread() wants both nbr_of_bytes and byte_offset to be a
multiple of the hardware value, which seems to be 512 in case of my
hard disk, and 2048 for cds and dvds.
Somehow I failed to see this on the pread man page.
What can I do to make it work?
Use appropriate values (see above).
Or, if this is impossible: how can I recognize beforehand those
filesystems which do not work with pread?
That now becomes a new question:
how to get this hardware value (hardware block-size?) before trying
to read?
This may be an artifact of opening up the /dev/rdisk directly.
With a regular file, pread works even when the requested data is not
sector-aligned.
This is correct. So the question should be:
When one opens a raw device via open(/dev/rdisk...) how does one get
the hardware sector size (which in this case is needed for read or
pread)?
It seems to be 512 for disks, 2048 for rotating media. But maybe there
is something better than trial and error?
Kind regards,
Gerriet.
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