linux-kernel - Re: [PATCH v2 8/8] docs: tmpfs: Add casefold options

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Message-ID: <871q20hev3.fsf@mailhost.krisman.be>
Date: Tue, 03 Sep 2024 12:38:24 -0400
From: Gabriel Krisman Bertazi <krisman@...e.de>
To: André Almeida <andrealmeid@...lia.com>
Cc: Hugh Dickins <hughd@...gle.com>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Alexander Viro <viro@...iv.linux.org.uk>,
  Christian Brauner <brauner@...nel.org>,  Jan Kara <jack@...e.cz>,
  krisman@...nel.org,  linux-mm@...ck.org,  linux-kernel@...r.kernel.org,
  linux-fsdevel@...r.kernel.org,  kernel-dev@...lia.com,  Daniel Rosenberg
 <drosen@...gle.com>,  smcv@...labora.com,  Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 8/8] docs: tmpfs: Add casefold options

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

> Document mounting options for casefold support in tmpfs.
>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
>  Documentation/filesystems/tmpfs.rst | 37 +++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>
> diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
> index 56a26c843dbe..ce24fb16979a 100644
> --- a/Documentation/filesystems/tmpfs.rst
> +++ b/Documentation/filesystems/tmpfs.rst
> @@ -241,6 +241,41 @@ 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:

insensitive

> +
> +================= ==============================================================
> +casefold          Enable casefold support at this mount point using the given
> +                  argument as the encoding standard. Currently only utf8
> +                  encodings are supported.
> +strict_encoding   Enable strict encoding at this mount point (disabled by
> +                  default). This means that invalid sequences will be rejected

Invalid sequences is not clear. Perhaps:

In this mode, the filesystem refuses to create file and directory with
names containing invalid UTF-8 characters.


> +                  by the file system.
> +================= ==============================================================
> +
> +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 fs_name /mytmpfs

cf_strict should be strict_encoding.

I keep wondering if we should accept 'casefold' without any argument to
just mean the latest encoding version available.  Sure, that is a
problem for filesystems that can be moved between systems, but for tmpfs
that is not a problem.  It is cumbersome to specify the version and most
will just want the latest.

> +    $ cd /mytmpfs # case-sensitive by default
> +    $ touch a; touch A
> +    $ ls
> +    A  a
> +    $ mkdir B
> +    $ cd b
> +    cd: The directory 'b' does not exist
> +    $ mkdir casefold_dir
> +    $ chattr +F casefold_dir/ # marking it as case-insensitive
> +    $ cd
> +    $ touch dir/a; touch dir/A
> +    $ ls dir
> +    a
> +    $ mkdir B
> +    $ cd b
> +    $ pwd
> +    /home/user/mytmpfs/casefold_dir/B

I don't think we need this example,  since it is just generic
how case-insensitiveness work.

>  
>  :Author:
>     Christoph Rohland <cr@....com>, 1.12.01
> @@ -250,3 +285,5 @@ RAM/SWAP in 10240 inodes and it is only accessible by root.
>     KOSAKI Motohiro, 16 Mar 2010
>  :Updated:
>     Chris Down, 13 July 2020
> +:Updated:
> +   André Almeida, 23 Aug 2024

-- 
Gabriel Krisman Bertazi