Date: Wed, 16 Dec 1998 14:06:04 +1030 From: Greg Lehey <grog@lemis.com> To: Dan Strick <dan@math.berkeley.edu> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Tape Driver Changes Proposed: Tape Early Warning Behaviour Message-ID: <19981216140604.H15815@freebie.lemis.com> In-Reply-To: <199812160331.TAA19404@math.berkeley.edu>; from Dan Strick on Tue, Dec 15, 1998 at 07:31:33PM -0800 References: <199812160331.TAA19404@math.berkeley.edu>
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On Tuesday, 15 December 1998 at 19:31:33 -0800, Dan Strick wrote: >> I can't see any particular reason to restrict the minor number format >> if it's not necessary. So we have 4 densities, n (<=4?) speeds and >> compression. That makes 5 bits. Then we have non-rewind, a maximum >> of 16 units per drive and (on a PC) probably not more than 16 >> controllers. A total of 14 bits of minor number out of the 24 >> available: in other words, there should be no problem finding a minor >> number format which fits. > > One good reason for restricting the minor number format is that 16384 > (i.e. 2^14) different entries for tape devices in /dev would be painful > beyound belief. You wouldn't automatically create all device nodes, just those that corresponded to real devices and their functions. > I claim that the idea of specifying tape drive operating parameters > via minor device number was a really bad idea from almost the very > beginning (unix v6 I believe) and should have been abandoned after > the ioctl() system call became available. How would you tell tar to make a backup, this time only, which didn't compress? If you did it with mt(1), how would you ensure that nobody dicked with the settings between your running mt(1) and tar(1)? Greg -- See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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