Date: Wed, 31 Oct 2007 11:21:21 -0600 From: Scott Long <scottl@samsco.org> To: Artem Kuchin <matrix@itlegion.ru> Cc: freebsd-current@freebsd.org Subject: Re: BIO_FLUSH on twe driver. Why is it not there? Message-ID: <4728B991.4020000@samsco.org> In-Reply-To: <0fbb01c81be1$37e698f0$0c00a8c0@Artem> References: <0fbb01c81be1$37e698f0$0c00a8c0@Artem>
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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. Scott
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