Date: Sat, 27 Jun 2009 19:31:13 +0300 From: Alexander Motin <mav@FreeBSD.org> To: =?UTF-8?B?VWxyaWNoIFNww7ZybGVpbg==?= <uqs@spoerlein.net> Cc: FreeBSD-Current <freebsd-current@freebsd.org>, scottl@freebsd.org Subject: Re: RFC: ATA to CAM integration patch Message-ID: <4A464951.6050604@FreeBSD.org> In-Reply-To: <20090627141412.GN31709@acme.spoerlein.net> References: <4A4517BE.9040504@FreeBSD.org> <20090627141412.GN31709@acme.spoerlein.net>
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Ulrich Spörlein wrote: > On Fri, 26.06.2009 at 21:47:26 +0300, Alexander Motin wrote: >> [Great stuff] >> - make sure that you will be able to boot if your SATA disk devices >> name change from some ad4 to ada0; > > I, personally, think this is not very good idea. People are used to > CAM-devices getting enumerated as da0, da1, etc. All the documentation > talks about ad0 for ATA and da0 (plus camcontrol) for SCSI, USB, > Firewire devices. We should understand difference between transport and command set. SPI, SAS, USB and FireWire are all just a transports for SCSI commands, and their disk devices use the same SCSI-command disk driver "da". ATA disks in this implementation are still use their native ATA commands, without translating to SCSI. So "ada" is a completely separate driver, operating disk devices supporting ATA, but _not_ a SCSI, command set. Whatever name we would use for it, "ada" still will be separate driver. It is not my whim. IMHO having two drivers with the same name is just a time bomb, which will create problems in future. If somebody sure that it won't, I will be glad to hear his technical opinion about how to manage that properly, for example, in newbus. > We also have fd0 and cd0 and should stick to > two-letter-plus-number codes. We also have a lot of longer disk driver names: aacd, amrd, mmcsd, ... > So either make them all ad0 or da0. I'd > vote for the latter, as that is what Linux is doing (more or less) and > people are already familiar with USB drives or new SATA drives showing > up as "SCSI drives, so they get the SCSI names". The main difference is that in our case SATA is not SCSI! We are not doing any emulation. CAM != SCSI any more! CAM = SCSI + ATA + whatever! -- Alexander Motin
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