From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 06/39] vfs: add f_op->pre_mmap() Date: Mon, 4 Jun 2018 01:48:27 -0700 Message-ID: <20180604084827.GE11333@infradead.org> References: <20180529144339.16538-1-mszeredi@redhat.com> <20180529144339.16538-7-mszeredi@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180529144339.16538-7-mszeredi@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Miklos Szeredi Cc: linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-unionfs@vger.kernel.org On Tue, May 29, 2018 at 04:43:06PM +0200, Miklos Szeredi wrote: > This is needed by overlayfs to be able to copy up a file from a read-only > lower layer to a writable layer when being mapped shared. When copying up, > overlayfs takes VFS locks that would violate locking order when nested > inside mmap_sem. > > Add a new f_op->pre_mmap method, which is called before taking mmap_sem. NAK. We really should not add multiple methods for mmap, and everytime this came up we found a better way to solve the problem instead. Most recent example was the socket zero copy receive code.