linux-kernel - Re: [PATCH v6 05/34] iov_iter: Change the direction macros into an enum

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Message-ID: <Y8h+naEJmlxIjyh1@ZenIV>
Date:   Wed, 18 Jan 2023 23:19:57 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 05/34] iov_iter: Change the direction macros into an
 enum

On Wed, Jan 18, 2023 at 11:17:41PM +0000, David Howells wrote:
> Al Viro <viro@...iv.linux.org.uk> wrote:
> 
> > > Change the ITER_SOURCE and ITER_DEST direction macros into an enum and
> > > provide three new helper functions:
> > > 
> > >  iov_iter_dir() - returns the iterator direction
> > >  iov_iter_is_dest() - returns true if it's an ITER_DEST iterator
> > >  iov_iter_is_source() - returns true if it's an ITER_SOURCE iterator
> > 
> > What for?  We have two valid values -
> > 	1) it is a data source
> > 	2) it is not a data source
> > Why do we need to store that as an enum?
> 
> Compile time type checking.

Huh?  int-to-enum conversion is quiet; it would catch explicit
huge constants, but that's it...