From: Andrew Morton <akpm@linux-foundation.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Andy Lutomirski <luto@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
LKML <linux-kernel@vger.kernel.org>,
Hugh Dickins <hughd@google.com>, Jann Horn <jannh@google.com>,
Khalid Aziz <khalid.aziz@oracle.com>,
Linux API <linux-api@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
marcandre.lureau@redhat.com, Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH -next 1/2] mm/memfd: make F_SEAL_FUTURE_WRITE seal more robust
Date: Sat, 24 Nov 2018 16:42:29 -0800 [thread overview]
Message-ID: <20181124164229.89c670b6e7a3530ef7b0a40c@linux-foundation.org> (raw)
In-Reply-To: <20181122230906.GA198127@google.com>
On Thu, 22 Nov 2018 15:09:06 -0800 Joel Fernandes <joel@joelfernandes.org> wrote:
> Android uses ashmem for sharing memory regions. We are looking forward to
> migrating all usecases of ashmem to memfd so that we can possibly remove
> the ashmem driver in the future from staging while also benefiting from
> using memfd and contributing to it. Note staging drivers are also not ABI
> and generally can be removed at anytime.
>
> One of the main usecases Android has is the ability to create a region and
> mmap it as writeable, then add protection against making any "future"
> writes while keeping the existing already mmap'ed writeable-region active.
> This allows us to implement a usecase where receivers of the shared
> memory buffer can get a read-only view, while the sender continues to
> write to the buffer. See CursorWindow documentation in Android for more
> details:
> https://developer.android.com/reference/android/database/CursorWindow
>
> This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
> To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
> which prevents any future mmap and write syscalls from succeeding while
> keeping the existing mmap active.
>
> A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week
> where we don't need to modify core VFS structures to get the same
> behavior of the seal. This solves several side-effects pointed by Andy.
> self-tests are provided in later patch to verify the expected semantics.
>
> [1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/
This changelog doesn't have the nifty test case code which was in
earlier versions?
next prev parent reply other threads:[~2018-11-25 0:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 5:21 [PATCH -next 1/2] mm/memfd: make F_SEAL_FUTURE_WRITE seal more robust Joel Fernandes (Google)
2018-11-20 5:21 ` [PATCH -next 2/2] selftests/memfd: modify tests for F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
2018-11-22 23:21 ` Joel Fernandes
2018-11-20 15:13 ` [PATCH -next 1/2] mm/memfd: make F_SEAL_FUTURE_WRITE seal more robust Andy Lutomirski
2018-11-20 18:39 ` Joel Fernandes
2018-11-20 20:07 ` Stephen Rothwell
2018-11-20 20:33 ` Andy Lutomirski
2018-11-20 20:47 ` Joel Fernandes
2018-11-20 21:02 ` Andy Lutomirski
2018-11-20 21:13 ` Joel Fernandes
2018-11-22 2:27 ` Andrew Morton
2018-11-22 3:25 ` Andy Lutomirski
2018-11-22 23:09 ` Joel Fernandes
2018-11-25 0:42 ` Andrew Morton [this message]
2018-11-25 0:47 ` Matthew Wilcox
2018-11-26 13:35 ` Joel Fernandes
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