Re: RFC: backporting GEOM to the 4.x branch
:I know you have other more important priorities, I did not expect you to port
:it instead of me. :-) Is someone already working on such a utility?
:
:> The current BUF/BIO model is very close to FreeBSD-4. We haven't done any
:> of the truely major bits of work on it yet (like changing the block
:> numbers to 64 bit byte offsets and things of that ilk).
:
:What other major changes that would affect what I would like to implement are
:planned? Anything else I should anticipate?
:
:> The only big difference relative to FreeBSD-4 is that the actual I/O
:> sequencing has changed slightly, and the device representing a labeled
:> disk is no longer overloaded onto the device reprsenting a 'raw' disk.
:
:That would indeed make it easier to implement dGDE, I'll take a closer look
:and study the code.
:
:ALeine
We've made a lot of little mods here and there, I don't remember them
all, but the only one that really counts is the new layering, and
that is mostly hidden by disk_create().
Check out any of the disk drivers. so e.g. look at ata-disk.c in
/usr/src/sys/dev/disk/ata/. It does this (where 'adp' is basically
just the softinfo for the driver):
dev = disk_create(adp->lun, &adp->disk, 0, &ad_cdevsw);
dev->si_drv1 = adp;
dev->si_iosize_max = 256 * DEV_BSIZE;
adp->dev = dev;
/* construct the disklabel */
bzero(&adp->disk.d_label, sizeof(struct disklabel));
adp->disk.d_label.d_secsize = DEV_BSIZE;
adp->disk.d_label.d_nsectors = adp->sectors;
adp->disk.d_label.d_ntracks = adp->heads;
adp->disk.d_label.d_ncylinders = adp->total_secs/(adp->heads*adp->sectors);
adp->disk.d_label.d_secpercyl = adp->sectors * adp->heads;
adp->disk.d_label.d_secperunit = adp->total_secs;
There are a couple of differences between the FreeBSD-5 way and
our way.
* We embed the disk structure in the softstruct rather then call
disk_alloc().
* Second, the disk device is not embedded in the disk structure but
instead returned by disk_create(), and the cdevsw template ias
passed to disk_create().
* We still have major/minor numbers, and will continue to have them
for some time to come. Look in ata-disk.c for typical setup of
the cdevsw structure. The cdevsw is a major number template.
The first argument to disk_create() is the unit number.
After that its almost the same. The returned 'dev' is purely for the
use of the block device. disk_create() will create a *DIFFERENT* dev
*internally* that is attached to the userland-accessible major,minor
number. The block device never touches the internal dev. So the driver
just uses the returned dev as the block device, and userland will wind
up using a different dev created by disk_create() which will do the
appropriate translation and label management.
-Matt
Matthew Dillon
<dillon@backplane.com>
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