Date: Sun, 5 Dec 1999 18:12:51 -0500 From: Garance A Drosihn <drosih@rpi.edu> To: Robert Watson <robert+freebsd@cyrus.watson.org>, Assar Westerlund <assar@sics.se> Cc: Wes Peters <wes@softweyr.com>, Randell Jesup <rjesup@wgate.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Portable way to compare struct stat's? Message-ID: <v04210101b4709542af7c@[128.113.24.47]> In-Reply-To: <Pine.BSF.3.96.991204151159.765A-100000@fledge.watson.org> References: <Pine.BSF.3.96.991204151159.765A-100000@fledge.watson.org>
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At 3:17 PM -0500 12/4/99, Robert Watson wrote:
>On 4 Dec 1999, Assar Westerlund wrote:
>
> > Garance A Drosihn <drosih@rpi.edu> writes:
> > > In the case of AFS, I think you'd want to expand the size of st_dev.
> > > All files in an AFS volume are "one device", I would think. If the
> > > "device" is gone (ie, the volume is not mounted), then all files in
> > > that "device" (volume) will not be available.
> >
> > I'm confused. Did you mean `st_ino' there? I agree that you want to
> > see the whole AFS space as a single device.
>
>I agree.
Well, I'm happy to have it that way if everyone prefers that, but I
really did mean to suggest that each AFS volume would be a separate
device. Not "all of AFS" as one device, or even "all of one AFS cell"
as one device. Do we have one device for "all NFS filesystems from all
hosts"? (my assumption is "no", but maybe I'm wrong (*)).
In local filesystems, a device is a partition on one hard disk. That
one partition could be unavailable (ie, "not mounted"), in which case
all files in that partition are not available. In AFS, the "mountable
quantity" is a volume. You can mount the same volume in multiple
places in AFS-land, in fact. If there's an AFS problem, you can be
in a situation where "most" of an AFS cell is up, but particular
volumes are not available because they are being salvaged. To me,
all of this seems to indicate that AFS volumes are pretty analogous
to what are used for devices on a local file system.
But really, any way we could arrange it would be fine with me...
(*) - I'm told that SGI's claim that all mounts (except lofs) will
have a unique st_dev, including NFS mounts. On the other hand,
I'm also told that linux seems to use the same st_dev value for
all NFS mounts from a given host. In my mind, the linux behavior
would suggest one st_dev value per AFS cell...
---
Garance Alistair Drosehn = gad@eclipse.acs.rpi.edu
Senior Systems Programmer or drosih@rpi.edu
Rensselaer Polytechnic Institute
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