linux-kernel - Re: [PATCH] fs: ufs: Remove switch statement from ufs_set_de

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Date:   Sun, 21 Oct 2018 00:07:34 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Phillip Potter <phil@...lpotter.co.uk>, dushistov@...l.ru,
        David.Laight@...lab.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: ufs: Remove switch statement from ufs_set_de_type
 function

On Sat, Oct 20, 2018 at 03:26:37PM -0700, Matthew Wilcox wrote:
> On Sat, Oct 20, 2018 at 11:09:57PM +0100, Phillip Potter wrote:
> > Remove switch statement from ufs_set_de_type function in fs/ufs/util.h
> > header and replace with simple assignment. For each case, S_IFx >> 12
> > is equal to DT_x, so in valid cases (mode & S_IFMT) >> 12 should give
> > us the correct file type. It is expected that for *nix compatibility
> > reasons, the relation between S_IFx and DT_x will not change. For
> > cases where the mode is invalid, upper layer validation catches this
> > anyway, so this improves readability and arguably performance by
> > assigning (mode & S_IFMT) >> 12 directly without any jump table
> > or conditional logic.
> 
> Shouldn't we also do this for other filesystems?  A quick scan suggests
> someone should at least look at xfs, ubifs, squashfs, romfs, ocfs2,
> nilfs2, hfsplus, f2fs, ext4, ext2, exofs, coda, cifs & btrfs.

Do what for other filesystems?  E.g. ext* has the type cached in directory
entry - as a straight enum, so encoding is needed.  Which we do.  ocfs2
is pretty certain to have it in ext*-compatible layout.  ubifs stores
them in another enum of its own (also handled).  XFS - another enum (present
on some layout variants), etc.

And... CIFS?  Seriously?  This stuff is about encoding used to cache the
file type in directory entry; how the bleeding hell would CIFS _client_
get anywhere near that?