remove sectors_per_block field from the ata channel
allow seccount to be set smaller than ATA_SECTORS_PER_BLOCK

add Copyright and license

In D7840#205182, @mav wrote:

I don't object committing this. I just want code style to be fixed according to style(9) first, for example, too long lines.

In D5473#151356, @editor_callfortesting.org wrote:

Support for FreeBSD 6 and older, even if for historical/academic purposes, is a topic that keeps coming up. Legacy systems come in all shapes and sizes and I can think of at least one point-of-sale vendor that spans generations of FreeBSD and other Unix systems.

Is this code in a usable state?

I think making it easy for the various interested parties to use it would better drive its direction.

FYI: You can also use my account 'dexter' on this system.

In D5473#117481, @grehan wrote:

Support for legacy o/s's has driven much of bhyve development. I'm all for this, though I agree there should be some consolidation of code that could be shared between ATA/ATAPI and AHCI.

In D5473#117352, @mav wrote:

In D5473#117346, @iateaca wrote:

The motivation is to run older versions of operating systems such as FreeBSD 4 which does not have AHCI drivers.
What do you mean by code duplication ? I think only the ATAPI CDROM logic could be common but the current implementation from AHCI can not be used with the ATA data strcutures. If we want to achive this, I think a redesign of AHCI ATAPI is required too.

I personally see quite little sense in supporting so old legacy guests. I agree that there can be "some cases", but I am not sure they worth the time spent and code size growth. Other then legacy guests support this code does not give us anything useful -- legacy ATA will be by definition much slower and less functional then its AHCI counterpart. It will require dozens of emulated register accesses per I/O, comparing to only several for AHCI, and won't support command queuing.

Though obviously nice and clean unified implementation would look better. In your patch you are one more time reimplementing some subsets of ATA and ATAPI commands handling, already done much wider for AHCI. It would be much better to have single device emulation code, interfacing with different controller code parts. But it would also take much more time (you are rigth that it would require existing code redesign), for the same little reason, so I am not sure how good is that idea. It needs investigation.

In D5473#117324, @mav wrote:

It was definitely significant amount of work, but I am not sure what motivation was behind it. Why do we need it after already having much more featured AHCI-based ATA/ATAPI emulation? Are there any significant OS not supporting AHCI? There is significant amount of code duplication between implementations, plus this one obviously requires more work to be complete.