From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <ed58ab1a31a87e6031e1c5061d2dfd8a@quanstro.net>
To: 9fans@cse.psu.edu
Subject: Re: device-specific qid.version behaviour (was Re: [9fans] QTCTL?)
From: erik quanstrom <quanstro@quanstro.net>
Date: Mon,  5 Nov 2007 10:27:49 -0500
In-Reply-To: <df49a7370711050635v2ad1bc1cu5ea5850b9951520a@mail.gmail.com>
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> um, i don't think i said that it was new behaviour. i did say that i th=
ought it
> was an abuse of the semantics, and i still think so. to me the devflopp=
y
> code you point to looks like it was just using the Chan as a
> convenient place to store

i think you should complain to presoto or rob.  it would be helpful to
do so in 1990.  you may need a time machine.

while you're at it, tell ken to spell "creat" with an "e".

and you need to complain about the abuse of wstat() to imply device
i/o flushing.

=E2=98=BA (just to remove any doubt)

seriously, the fewer rigid rules we make for 9p,
the more adaptable it will be.

the history migration process i built for kenfs
(/n/sources/contrib/quanstro/history.ms)
insures that for any two files on the original fs,

	a.file1.qid.vers =3D=3D a.file2.qid.vers =3D>
		b.file1.qid.vers =3D=3D b.file2.qid.vers.

russ thinks this is too strong an assumption in general.
i was just targeting fileservers like kenfs or fossil.
but in general, russ is correct.  this wouldn't work
for devsd data files, for the reasons you mention.

> turning things around, by providing device-specific versioning behavior=
,
> you can end up with clients that won't work well when run over normal
> files. if a client expects the version number to change only when the
> media changes, then it's quite likely to be fairly surprised if
> the version number changes every time it writes some data.

the fact is, you can't deal with a physical disk like /dev/sdE0/data
in the same way you can deal with a regular fileserver.  clients
that make strong assumptions about ownership, dates or
qid.vers are going to get burned by devices serving up physical
media.

try doing ls -lt /mail/fs/mbox.

- erik