From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alasdair G Kergon Subject: Re: [RFC PATCH 5/5] multipathd: RFC add new polling dmevents waiter thread Date: Tue, 13 Feb 2018 01:13:34 +0000 Message-ID: <20180213011334.GG16558@agk-dp.fab.redhat.com> References: <1518239251-29392-1-git-send-email-bmarzins@redhat.com> <1518239251-29392-6-git-send-email-bmarzins@redhat.com> <1518292553.2937.44.camel@suse.com> <20180212231802.GA14513@octiron.msp.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20180212231802.GA14513@octiron.msp.redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Benjamin Marzinski Cc: device-mapper development , Martin Wilck List-Id: dm-devel.ids On Mon, Feb 12, 2018 at 05:18:02PM -0600, Benjamin Marzinski wrote: > It is the DM_EXISTS_FLAG. It's defined in libdm/ioctl/libdm-iface.c in > the lvm2 source. It is unconditionally set on all dm control ioctls > from libdevmapper by _do_dm_ioctl() (also in libdm/ioctl/libdm-iface.c). > I don't know the reason for this. I don't see anything that uses it in > driver/md/dm-ioctl.c, and I see that line in the libdm source has a > /* FIXME */ next to it. On the other hand, all I'm trying to do here is > run the same ioctl that libdevmapper would if it supported this command, > and there may well be a reason for it that I'm missing. DM_EXISTS_FLAG indicates that the device the ioctl referenced exists. If you performed certain queries and the device was not found, you got a successful return but without this flag. In the dim and distant past this flag was handled kernel-side. Later, we dropped it but left that userspace code emulating it. The FIXMEs were just saying that the library code could be cleaned up too one day. Ref. https://lwn.net/Articles/38512/ Alasdair