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[91.12.101.41]) by smtp.gmail.com with ESMTPSA id o12sm2043243wrw.73.2021.10.06.08.47.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Oct 2021 08:48:00 -0700 (PDT) Subject: Re: [RFC] pgflags_t To: Al Viro Cc: Matthew Wilcox , linux-mm@kvack.org, Kent Overstreet , Johannes Weiner , linux-fsdevel@vger.kernel.org References: <106400c5-d3f2-e858-186a-82f9b517917b@redhat.com> <21ce511e-7cde-8bdb-b6c6-e1278681ebf6@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: <514dfafb-6a98-65ff-a9a7-421bbc2a0cec@redhat.com> Date: Wed, 6 Oct 2021 17:47:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 3AEA55073D49 X-Stat-Signature: a3pjzuupeirz6ayrkjawk63kob3m9mod Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=RtVt1zKH; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf05.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-HE-Tag: 1633535286-513508 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 06.10.21 17:46, Al Viro wrote: > On Wed, Oct 06, 2021 at 05:32:39PM +0200, David Hildenbrand wrote: > >> It feels to me like using __bitwise for access checks and then still >> modifying the __bitwise fields randomly via a backdoor. But sure, if it >> works, I'll be happy if we can use that. > > __bitwise == "can't do anything other than bitwise operations without > an explicit force-cast". All there is to it. Hell, the very first > use had been for things like __le32 et.al., where the primitives > very much do non-bitwise accesses. They are known to be safe (== > do the same thing regardless of the host endianness). Internally > they contain force-casts, precisely so that the caller wouldn't > need to. Thanks for clarifying that :) -- Thanks, David / dhildenb