linux-kernel - Re: [PATCH] fs/9p: Add new options to Documentation

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Date:   Mon, 27 Mar 2023 17:38:41 +0200
From:   Christian Schoenebeck <linux_oss@...debyte.com>
To:     v9fs-developer@...ts.sourceforge.net,
        Eric Van Hensbergen <ericvh@...nel.org>
Cc:     asmadeus@...ewreck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/9p: Add new options to Documentation

On Monday, March 27, 2023 5:05:52 AM CEST Eric Van Hensbergen wrote:
> Need to update the documentation for new mount flags
> and cache modes.
> 
> Signed-off-by: Eric Van Hensbergen <ericvh@...nel.org>
> ---
>  Documentation/filesystems/9p.rst | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/filesystems/9p.rst b/Documentation/filesystems/9p.rst
> index 0e800b8f73cc..6d257854a02a 100644
> --- a/Documentation/filesystems/9p.rst
> +++ b/Documentation/filesystems/9p.rst
> @@ -78,19 +78,18 @@ Options
>    		offering several exported file systems.
>  
>    cache=mode	specifies a caching policy.  By default, no caches are used.
> -
> -                        none
> -				default no cache policy, metadata and data
> -                                alike are synchronous.
> -			loose
> -				no attempts are made at consistency,
> -                                intended for exclusive, read-only mounts
> -                        fscache
> -				use FS-Cache for a persistent, read-only
> -				cache backend.
> -                        mmap
> -				minimal cache that is only used for read-write
> -                                mmap.  Northing else is cached, like cache=none
> +		Modes are progressive and inclusive.  For example, specifying fscache
> +		will use loose caches, writeback, and readahead.  Due to their
> +		inclusive nature, only one cache mode can be specified per mount.

I would highly recommend to rather specify below for each option "this option
implies writeback, readahead ..." etc., as it is not obvious otherwise which
option would exactly imply what. It is worth those extra few lines IMO to
avoid confusion.

> +
> +			=========	=============================================
> +			none		no cache of file or metadata
> +			readahead	readahead caching of files
> +			writeback	delayed writeback of files
> +			mmap		support mmap operations read/write with cache
> +			loose		meta-data and file cache with no coherency
> +			fscache		use FS-Cache for a persistent cache backend
> +			=========	=============================================
>  
>    debug=n	specifies debug level.  The debug level is a bitmask.
>  
> @@ -137,6 +136,10 @@ Options
>    		This can be used to share devices/named pipes/sockets between
>  		hosts.  This functionality will be expanded in later versions.
>  
> +  directio	bypass page cache on all read/write operations
> +
> +  ignoreqv	ignore qid.version==0 as a marker to ignore cache
> +
>    noxattr	do not offer xattr functions on this mount.
>  
>    access	there are four access modes.
>