Subject: Re: representation of persistent device status, was Re: devfs, was Re: ptyfs...
To: Bill Studenmund <email@example.com>
From: Daniel Carosone <firstname.lastname@example.org>
Date: 11/20/2004 17:08:56
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On Fri, Nov 19, 2004 at 06:41:13PM -0800, Bill Studenmund wrote:
> Note: while I've mentioned some aspects of a devfs that help
> "user-friendly workstations," I also am thinking of server-class machines=
> too. These changes will really help with disks on SANs.
Elsewhere in this thread, I specifically used the example of WWN-based
locators for FC-AL disks, possibly with multi-pathing, in recognition
of exactly this point. :-)
> I expect we'll come up with something like "dstat"(2). This idea is
> quite rough, and certainly open to comment. The idea is to permit
> userland to querry the bindings (locators) for a device. Thus
> tripwire will be able to make sure the locators for a node won't
> move around.
See my "symdev" proposal for one representation of essentially this
For the purposes of illustration, i'm imagining that locator strings
in these symlinks are analogous to LDAP query search strings. Lest
anyone get hung up on the syntax of the example, perhaps I'll suggest
that they instead be SQL strings, just to make it clear that I'm not
presuming any particular syntax, but that they should be simple
strings that can be handled and stored easily, whether in symlinks, a
devfs-persistence-file, or a config-assist daemon config file.
They're a way to express matching against a "locators database" in the
config namespace in the kernel. A device might have a number of names
in this namespace, to help itself get found by these search strings
(c/b,major,minor being one of the forms of its name, verily).
Depending how the search strings are written, they might be entirely
and utterly specific to a particular node, or they might be a looser
search that permits variations: "a msdosfs wedge called 'my pics' on a
umass device, in any slot" or "the first scsi tape drive found" or
perhaps even "the first nic found, any driver".
If you want a locked down system, you use highly specific search
strings; if you want a more flexible set of names in /dev, you use a
looser set of searches. In much the same way that you might hardwire
or wildcard devices to locators in config(8) files now. In either
case, if someone changes your search strings on you, tripwire can
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