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

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Date:   Wed, 17 Oct 2018 10:11:47 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Phillip Potter' <phil@...lpotter.co.uk>,
        "dushistov@...l.ru" <dushistov@...l.ru>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH] fs: ufs: Remove switch statement from ufs_set_de_type
 function

From: Phillip Potter
> Sent: 17 October 2018 11:08
> 
> 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. For invalid cases, upper layer validation
> catches this anyway, so this improves readability and arguably
> performance by assigning (mode & S_IFMT) >> 12 directly.
> 
...
> -	case S_IFIFO:
> -		de->d_u.d_44.d_type = DT_FIFO;
> -		break;
> -	default:
> -		de->d_u.d_44.d_type = DT_UNKNOWN;
> -	}
> +	de->d_u.d_44.d_type = (mode & S_IFMT) >> S_SHIFT;

This requires that the two sets of constants are correctly aligned.
If they aren't defined in terms of each other then you probably
ought to add compile-time asserts that the values match.

	David

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