linux-kernel - Re: [PATCH] fs: ufs: Convert ufs_set_de

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Message-ID: <20181002083100.GB4263@pathfinder>
Date:   Tue, 2 Oct 2018 09:31:00 +0100
From:   Phillip Potter <phil@...lpotter.co.uk>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     dushistov@...l.ru, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: ufs: Convert ufs_set_de_type to use lookup table

On Tue, Oct 02, 2018 at 03:28:14AM +0100, Al Viro wrote:
> On Mon, Oct 01, 2018 at 04:33:10PM +0100, Phillip Potter wrote:
> > Modify ufs_set_de_type function in fs/ufs/util.h to use a lookup
> > table rather than a switch statement, as per the TODO comment.
> 
> Brittle, that...   Something like fs/ext2/dir.c approach (that is,
> #define S_SHIFT 12
> static unsigned char ext2_type_by_mode[S_IFMT >> S_SHIFT] = {
>         [S_IFREG >> S_SHIFT]    = EXT2_FT_REG_FILE,
>         [S_IFDIR >> S_SHIFT]    = EXT2_FT_DIR,
>         [S_IFCHR >> S_SHIFT]    = EXT2_FT_CHRDEV,
>         [S_IFBLK >> S_SHIFT]    = EXT2_FT_BLKDEV,
>         [S_IFIFO >> S_SHIFT]    = EXT2_FT_FIFO,
>         [S_IFSOCK >> S_SHIFT]   = EXT2_FT_SOCK,
>         [S_IFLNK >> S_SHIFT]    = EXT2_FT_SYMLINK,
> };
> in there) would be saner, IMO.  Note that DT_UNKNOWN is zero, so the
> array elements lacking an explicit initializer will end up with that.
> 
> What's more, the values are ->i_mode >> 12 or 0, depending upon the
> value being valid.  And since the upper layers do validate the type,
> I'd consider simply using (inode->i_mode & S_IFMT) >> 12 there.
> Unlike ext2, ufs stores straight bits 12..15 there (ext2 uses an
> enum with sequential values instead; e.g. regular files are encoded
> as 1 there, not 8 as on ufs)...

Dear Al,

Thank you for taking time to offer your feedback, I really appreciate
it. I will rework this patch this evening and resubmit.

Regards,
Phil