linux-kernel - Re: [RFC PATCH 4/4] docs: tmpfs: Add casefold options

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Date:   Tue, 23 Mar 2021 18:19:19 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>, smcv@...labora.com,
        kernel@...labora.com, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniel Rosenberg <drosen@...gle.com>
Subject: Re: [RFC PATCH 4/4] docs: tmpfs: Add casefold options

André Almeida <andrealmeid@...labora.com> writes:

> Document mounting options to enable casefold support in tmpfs.
>
> Signed-off-by: André Almeida <andrealmeid@...labora.com>
> ---
>  Documentation/filesystems/tmpfs.rst | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
> index 0408c245785e..84c87c309bd7 100644
> --- a/Documentation/filesystems/tmpfs.rst
> +++ b/Documentation/filesystems/tmpfs.rst
> @@ -170,6 +170,32 @@ So 'mount -t tmpfs -o size=10G,nr_inodes=10k,mode=700 tmpfs /mytmpfs'
>  will give you tmpfs instance on /mytmpfs which can allocate 10GB
>  RAM/SWAP in 10240 inodes and it is only accessible by root.
>  
> +tmpfs has the following mounting options for case-insesitive lookups support:
> +
> +=========   ==============================================================
> +casefold    Enable casefold support at this mount point using the given
> +            argument as enconding. Currently only utf8 encondings are supported.
> +cf_strict   Enable strict casefolding at this mouting point (disabled by
> +            default). This means that invalid strings should be reject by the
> +            file system.

strict mode refers to the encoding, not exactly casefold.  Maybe we
could have a parameter encoding_flags that accepts the flag 'strict'.
This would make it closer to the ext4 interface.  Alternatively, call
this option strict_encoding.

> +=========   ==============================================================
> +
> +Note that this option doesn't enable casefold by default, one needs to set
> +casefold flag per directory, setting the +F attribute in an empty directory. New
> +directories within a casefolded one will inherit the flag.
> +
> +Example::
> +
> +    $ mount -t tmpfs -o casefold=utf8-12.1.0,cf_strict tmpfs /mytmpfs
> +    $ cd /mytmpfs
> +    $ touch a; touch A
> +    $ ls
> +    A  a
> +    $ mkdir dir
> +    $ chattr +F dir
> +    $ touch dir/a; touch dir/A
> +    $ ls dir
> +    a
>  
>  :Author:
>     Christoph Rohland <cr@....com>, 1.12.01

-- 
Gabriel Krisman Bertazi