Date: Wed, 31 Oct 2007 21:39:49 +0300 From: "Artem Kuchin" <matrix@itlegion.ru> To: "Scott Long" <scottl@samsco.org> Cc: freebsd-current@freebsd.org Subject: Re: BIO_FLUSH on twe driver. Why is it not there? Message-ID: <001a01c81bef$54496910$0c00a8c0@Artem> References: <0fbb01c81be1$37e698f0$0c00a8c0@Artem> <4728B991.4020000@samsco.org>
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Scott Long wrote: > Artem Kuchin wrote: >> 7-BETA1 >> gjournal complained that BIO_FLUSH is not supported by the driver. >> That is twe driver. >> However, twe is working via scsi subsystem and the authour of >> gjournal said somewhere that he >> has had implemeneted BIO_FLISH for scsi and he specifically mentioned >> that he has tested twe and twa and they both support BIO_FLUSH. >> Then why BIO_FLISH is not supported now? >> > > The twe driver does NOT operate under the SCSI subsystem. As for > flush semantics in SCSI, they are much better done with ordered tags, > not explicit SYNC_CACHE commands. That's not to say that SYNC_CACHE > won't work (well, except for random devices that will hang with it in > unpredictable ways, but no one seems to care about that little > detail). Unfortunately, BIO_ORDERED was removed from the FreeBSD > block layer several years ago. How is this possible? [QUOTE:] URL:http://unix.derkeiler.com/Mailing-Lists/FreeBSD/current/2006-08/msg00179.html DATE SOURCE: AUGUST 2006 freebsd-current maillis) WHO: Pawel Jakub Dawidek Unfortunately I'm not able to implement BIO_FLUSH to all out storage drivers. Currently BIO_FLUSH is supported by ata(4) (/dev/a[dr]X), da(4) and amr(4). That's the theory. I'm using standard SCSI commands for this. From the tests we made it seems that it works ok with twa(4)/twe(4). I'd still be glad if someone with SCSI/CAM foo could look at the code. [ENDQUOTE] So what changed since then? -- Artem
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