linux-kernel - Re: [PATCH] iov_iter: Use __bitwise with the extraction

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Message-ID: <b8082dcd-632b-bf75-061c-143cca6fa70d@redhat.com>
Date:   Thu, 26 Jan 2023 11:41:40 +0100
From:   David Hildenbrand <david@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        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>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH] iov_iter: Use __bitwise with the extraction_flags

On 26.01.23 11:33, David Howells wrote:

> Interestingly, things like __be32 are __bitwise.  I wonder if that actually
> makes sense or if it was just convenient so stop people doing arithmetic on
> them.  I guess doing AND/OR/XOR on them isn't a problem provided both
> arguments are appropriately byte-swapped.

I recall that __be32 and friends were one of the early users of 
__bitwise in the kernel. And the reason IIRC was exactly that: detect 
when no proper conversion was performed using static code analysis 
(Sparse). While some operations might make sense, the abuse is much more 
likely.


LGTM, thanks!

-- 
Thanks,

David / dhildenb