Re: [patch 2/5] drivers/base/memory.c: indicate all memory blocks as removable

From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Hildenbrand <david@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Dan Williams <dan.j.williams@intel.com>,
	 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	 Karel Zak <kzak@redhat.com>, Linux-MM <linux-mm@kvack.org>,
	Michal Hocko <mhocko@kernel.org>,  Michal Hocko <mhocko@suse.com>,
	mm-commits@vger.kernel.org, ndfont@gmail.com,
	 pbadari@us.ibm.com, Rafael Wysocki <rafael@kernel.org>,
	rcj@linux.vnet.ibm.com,  stable <stable@vger.kernel.org>,
	steve.scargall@intel.com
Subject: Re: [patch 2/5] drivers/base/memory.c: indicate all memory blocks as removable
Date: Sun, 29 Mar 2020 11:28:00 -0700	[thread overview]
Message-ID: <CAHk-=wg+UUK7hj9xKhoDfqXG4bCrOtTA-_WPoFemU_=1G_NHGQ@mail.gmail.com> (raw)
In-Reply-To: <b80d7cea-a8f7-11c9-66fa-bdc272bdf099@redhat.com>

On Sun, Mar 29, 2020 at 11:04 AM David Hildenbrand <david@redhat.com> wrote:
>
>
> What I received via the mailing list (e.g., linux-mm@kvack.org)
>
> Message-Id: <20200128093542.6908-1-david@redhat.com>
> MIME-Version: 1.0
> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13
> 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: <linux-mm.kvack.org>
> [...]
> X-Mimecast-Spam-Score: 1
> Content-Type: text/plain; charset=US-ASCII
> Content-Transfer-Encoding: quoted-printable
> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4
> [...]
>
> And a lot of this MIME crap.

Well, that may still be a perfectly fine email.

Yes, it has the MIME crap, but it also has that

  Content-Transfer-Encoding: quoted-printable

which should tell all users how to _handle_ that MIME crap.

It's sad that people in this day and age still don't just handle

  Content-Transfer-Encoding: 8bit

and just send it on untouched, but SMTP certainly encourages that bad
behavior of "convert to 7-bit MIME crap", because in theory there
could be SMTP servers out there that can't handle anything 8-bit or
with longer lines.

Those SMTP servers should just be scrapped and people told not to use
them, but sadly that's not the approach email people have taken.
They've taken the approach that old garbage SMTP servers should be
allowed to exist and destroy email for the rest of us.

> I have no idea if such a conversion is expected to be done.

It is (sadly) expected to be done by a lot of mail software.

But the problem is that some part of your email handling code then
doesn't _undo_ the MIME conversion, and leaves the MIME turds alone,
while then that "Content-Transfer-Encoding: quoted-printable" got
lost.

Do you at any point end up using a raw mbox and cut-and-pasting stuff?
Reading email in a broken mail-reader that doesn't undo MIME? Because
that's the usual way that these kinds of turds get copied.. Using raw
emails without honoring or taking that "Content-Transfer-Encoding"
into account.

                   Linus