Re: O_DIRECT alignment requirements ?

[Rob van Nieuwkerk]

> On Wed, Apr 09, 2003 at 11:09:23PM +0200, Rob van Nieuwkerk wrote:
> > But a friend of mine uses O_DIRECT with 2.4 kernels to read *individual*
> > single harddisk sectors of 512 bytes !  He claims that my original
> > theory is the right one and that you can read 512 byte chunks on 512
> > byte bounderies (he uses the complete device eg. /dev/hda).
> 
> 	Well, how does your friend access /dev/hda?  Is he using raw
> devices?

Hi all,

OK, I checked again with him.  It turns out there was some confusion.
He does read in *1024* byte chunks after all (accessing /dev/hdX
directly) ..

But I still need to do 512 byte chunks myself (*).
I understand that this can be done with the the raw device construction ?

Would it also be possible to change the device blocksize with a BLKBSZSET
ioctl() to 512 and do 512 byte transfers after that ?

	greetings,
	Rob van Nieuwkerk

*: you might wonder why I'm so obsessed with 512 transfers ..
   The reason is that I'm working with a USB device (driver) that
   dies when there is too much CompactFlash IDE access (because
   of data-records logged to the CF).  I want to have the absolute
   minimum amount of disk-access.