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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Davidlohr Bueso <dbueso@suse.de>, Jason Baron <jbaron@akamai.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 09/15] epoll: introduce stand-alone helpers for polling from userspace
Date: Wed, 9 Jan 2019 09:29:18 -0800
Message-ID: <CAHk-=whD=pjn4myRysuyeAiNOxv49XVQuJaE7Xd6ZBEMf6eXtA@mail.gmail.com> (raw)
In-Reply-To: <20190109164025.24554-10-rpenyaev@suse.de>

On Wed, Jan 9, 2019 at 8:40 AM Roman Penyaev <rpenyaev@suse.de> wrote:
>
> ep_vrealloc*()
>     realloc user header, user index or bitmap memory

What? No.

This is wrong, it's much too complicated. And because your
'vrealloc()' doesn't follow the normal realloc rules, it looks both
confusing and buggy, and people have to remember that "oh, vrealloc()
isn't actually vrealloc(), it's really vdupalloc()".

Your other patch to allow users to apparently also do mremap of these
things seems entirely wrongheaded too. Especially when you then have
magical rules for vm_pgoff, which is one of the things that unmapping
parts of a mmap will touch.

So I say no, no, no. This is all *much* too complicated, and the
interfaces are mis-designed to be overly generous to people doing odd
and pointless things.

If you can't have a fixed-size user buffer that stays in one place,
don't even bother.

             Linus

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 16:40 [RFC 00/15] epoll: support pollable epoll " Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 01/15] mm/vmalloc: add new 'alignment' field for vm_struct structure Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 02/15] mm/vmalloc: move common logic from __vmalloc_area_node to a separate func Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 03/15] mm/vmalloc: introduce new vrealloc() call and its subsidiary reach analog Roman Penyaev
2019-01-09 16:50   ` Matthew Wilcox
2019-01-10 10:08     ` Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 04/15] epoll: move private helpers from a header to the source Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 05/15] epoll: introduce user header structure and user index for polling from userspace Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 06/15] epoll: introduce various of helpers for user structure lengths calculations Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 07/15] epoll: extend epitem struct with new members for polling from userspace Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 08/15] epoll: some sanity flags checks for epoll syscalls for polled epfd " Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 09/15] epoll: introduce stand-alone helpers for polling " Roman Penyaev
2019-01-09 17:29   ` Linus Torvalds [this message]
2019-01-10 10:03     ` Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 10/15] epoll: support polling from userspace for ep_insert() Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 11/15] epoll: offload polling to a work in case of epfd polled from userspace Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 12/15] epoll: support polling from userspace for ep_remove() Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 13/15] epoll: support polling from userspace for ep_modify() Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 14/15] epoll: support polling from userspace for ep_poll() Roman Penyaev
2019-01-09 16:40 ` [RFC PATCH 15/15] epoll: support mapping for epfd when polled from userspace Roman Penyaev

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