linux-kernel - Re: [RFC PATCH] 9p: case-insensitive host filesystems

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Message-ID: <YmMItCb97KqegQw5@codewreck.org>
Date:   Sat, 23 Apr 2022 04:57:40 +0900
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Christian Schoenebeck <qemu_oss@...debyte.com>
Cc:     qemu-devel@...gnu.org, Will Cohen <wwcohen@...il.com>,
        Greg Kurz <groug@...d.org>,
        Michael Roitzsch <reactorcontrol@...oud.com>,
        Keno Fischer <keno@...iacomputing.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>
Subject: Re: [RFC PATCH] 9p: case-insensitive host filesystems

Christian Schoenebeck wrote on Fri, Apr 22, 2022 at 08:02:46PM +0200:
> So maybe it's better to handle case-insensitivity entirely on client side? 
> I've read that some generic "case fold" code has landed in the Linux kernel 
> recently that might do the trick?

I haven't tried, but settings S_CASEFOLD on every inodes i_flags might do
what you want client-side.
That's easy enough to test and could be a mount option

Even with that it's possible to do a direct open without readdir first
if one knows the path and I that would only be case-insensitive if the
backing server is case insensitive though, so just setting the option
and expecting it to work all the time might be a little bit
optimistic... I believe guess that should be an optimization at best.

Ideally the server should tell the client they are casefolded somehow,
but 9p doesn't have any capability/mount time negotiation besides msize
so that's difficult with the current protocol.

-- 
Dominique | Asmadeus