Hello Erik,
I really appreciate what you replied to me. :)
On Mon, May 21, 2007 at 12:04:49PM +0200, Erik Mouw wrote:
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> On Mon, May 21, 2007 at 07:46:39AM +0900, Seongsu Lee wrote:
> > I am playing with block devices but I need help.
> >
> > [1]
> > I want to override the do_hd_requrst() of a user-specified
> > hard disk. For the work, I want to iterate in 'gendisk's
> > without modifying the current source. (ex: hd.c)
> > 'struct gendisk' is static variables and I have no idea
> > to access it.
>
> So you want to change something without having to change something.
> Sounds a bit impossible to me.
>
> > How can I override the request function of a gendisk?
>
> Why do you want to override it in the first place? What is the goal?
> Maybe there are much better ways to achieve what you try to do.
What I want to do is to use my own do_request function which
redirect I/O request into physically another device under the
condition.
I found that I can get reference pointer of IDE device driver,
struct ide_disk_obj by a function, bdget() and a macro containter_of.
struct block_device *b = bdget(dev);
idkp = container_of(g->private_data, struct ide_disk_obj, driver):
And I overrided the do_request() function by:
do_request_oldp = idkp->driver->do_request;
idkp->driver->do_request = ide_do_rw_disk_my_own;
I hope this may help somebody.
> > [2]
> > Is it right that the Linux use only one request queue for
> > all the IDE/ATA-based block devices?
> > I looked hd_init() in drivers/ide/lagacy/hd.c and found
> > that a single request queue, hd_queue is used for all the
> > devices. Am I right?
>
> For the legacy devices maybe, yeah. Note that the legacy driver is
> almost never used unless you have a very old 386 system with MFM drives
> or so. Anything slightly more modern uses the non-legacy IDE drivers or
> the libata SATA/PATA drivers which use a request queue per device.
You are right. hd.c in drivers/ide/lagacy directory is a code for
very old device. I didn't know it.
Modern disks such as IDE/ATA or S-ATA based use per-drive rqeust queue.
Thank you very much.
--
Seongsu's personal blog - http://www.senux.com/
But what can you do with it? -- ubiquitous cry from
Linux-user partner. (Submitted by Andy Pearce,
ajp@xxxxxxxxxxxxxxxx)
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