linux-ext4 - Re: [PATCH RFC v2 00/13] NLS/UTF-8 Case-Insensitive lookups for ext4 and VFS proposal

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Message-ID: <20180125031650.GU13338@ZenIV.linux.org.uk>
Date:   Thu, 25 Jan 2018 03:16:50 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Gabriel Krisman Bertazi <krisman@...labora.co.uk>
Cc:     tytso@....edu, david@...morbit.com, olaf@....com,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        alvaro.soliverez@...labora.co.uk, kernel@...ts.collabora.co.uk
Subject: Re: [PATCH RFC v2 00/13] NLS/UTF-8 Case-Insensitive lookups for ext4
 and VFS proposal

On Thu, Jan 25, 2018 at 12:53:36AM -0200, Gabriel Krisman Bertazi wrote:

> The second proposal is related to the VFS layer:
> 
> (2) Enable Insensitive lookup support on a per-mountpoint basis,
> via a MS_CASEFOLD flag, with the ultimate goal of supporting a
> case-insensitive bind mount of a subtree, side-by-side with a
> sensitive version of the filesystem.

First reaction: No.  With the side of HELL NO.

Your ultimate goal sounds utterly insane - dcache tree must be shared
for all mounts.  Moreover, "would these two names refer to the same
object" can not be mount-dependent.  Not going to happen.

Please, post the description of what you are planning to do.
Detailed.  I'm not saying that it's 100% impossible to do correctly,
but I'm _very_ sceptical about the feasibility.

I'm certainly not going to ACK any VFS changes until you convince
me that this thing can be done with sane semantics.