Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753534AbbFXPJP (ORCPT ); Wed, 24 Jun 2015 11:09:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42361 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752620AbbFXPJM (ORCPT ); Wed, 24 Jun 2015 11:09:12 -0400 Date: Wed, 24 Jun 2015 17:08:56 +0200 From: "Michael S. Tsirkin" To: Igor Mammedov Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH RFC] vhost: add ioctl to query nregions upper limit Message-ID: <20150624170223-mutt-send-email-mst@redhat.com> References: <1435153753-2686-1-git-send-email-mst@redhat.com> <20150624160727.2e0f542f@nial.brq.redhat.com> <20150624161606-mutt-send-email-mst@redhat.com> <20150624165229.4f8bf82b@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150624165229.4f8bf82b@nial.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5060 Lines: 111 On Wed, Jun 24, 2015 at 04:52:29PM +0200, Igor Mammedov wrote: > On Wed, 24 Jun 2015 16:17:46 +0200 > "Michael S. Tsirkin" wrote: > > > On Wed, Jun 24, 2015 at 04:07:27PM +0200, Igor Mammedov wrote: > > > On Wed, 24 Jun 2015 15:49:27 +0200 > > > "Michael S. Tsirkin" wrote: > > > > > > > Userspace currently simply tries to give vhost as many regions > > > > as it happens to have, but you only have the mem table > > > > when you have initialized a large part of VM, so graceful > > > > failure is very hard to support. > > > > > > > > The result is that userspace tends to fail catastrophically. > > > > > > > > Instead, add a new ioctl so userspace can find out how much kernel > > > > supports, up front. This returns a positive value that we commit to. > > > > > > > > Also, document our contract with legacy userspace: when running on an > > > > old kernel, you get -1 and you can assume at least 64 slots. Since 0 > > > > value's left unused, let's make that mean that the current userspace > > > > behaviour (trial and error) is required, just in case we want it back. > > > > > > > > Signed-off-by: Michael S. Tsirkin > > > > Cc: Igor Mammedov > > > > Cc: Paolo Bonzini > > > > --- > > > > include/uapi/linux/vhost.h | 17 ++++++++++++++++- > > > > drivers/vhost/vhost.c | 5 +++++ > > > > 2 files changed, 21 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > > > index ab373191..f71fa6d 100644 > > > > --- a/include/uapi/linux/vhost.h > > > > +++ b/include/uapi/linux/vhost.h > > > > @@ -80,7 +80,7 @@ struct vhost_memory { > > > > * Allows subsequent call to VHOST_OWNER_SET to succeed. */ > > > > #define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02) > > > > > > > > -/* Set up/modify memory layout */ > > > > +/* Set up/modify memory layout: see also VHOST_GET_MEM_MAX_NREGIONS below. */ > > > > #define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory) > > > > > > > > /* Write logging setup. */ > > > > @@ -127,6 +127,21 @@ struct vhost_memory { > > > > /* Set eventfd to signal an error */ > > > > #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) > > > > > > > > +/* Query upper limit on nregions in VHOST_SET_MEM_TABLE arguments. > > > > + * Returns: > > > > + * 0 < value <= MAX_INT - gives the upper limit, higher values will fail > > > > + * 0 - there's no static limit: try and see if it works > > > > + * -1 - on failure > > > > + */ > > > > +#define VHOST_GET_MEM_MAX_NREGIONS _IO(VHOST_VIRTIO, 0x23) > > > > + > > > > +/* Returned by VHOST_GET_MEM_MAX_NREGIONS to mean there's no static limit: > > > > + * try and it'll work if you are lucky. */ > > > > +#define VHOST_MEM_MAX_NREGIONS_NONE 0 > > > is it needed? we always have a limit, > > > or don't have IOCTL => -1 => old try and see way > > > > > > > +/* We support at least as many nregions in VHOST_SET_MEM_TABLE: > > > > + * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */ > > > > +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64 > > > ^^^ not used below, > > > if it's for legacy then perhaps s/DEFAULT/LEGACY/ > > > > The assumption was that userspace detecting old kernels will just use 64, > > this means we do want a flag to get the old way. > > > > OTOH if you won't think it's useful, let me know. > this header will be synced into QEMU's tree so that we could use this define there, > isn't it? IMHO then _LEGACY is more exact description of macro. > > As for 0 return value, -1 is just fine for detecting old kernels (i.e. try and see if it works), so 0 looks unnecessary but it doesn't in any way hurt either. > For me limit or -1 is enough to try fix userspace. OK. Do you want to try now before I do v2? > > > > > > + > > > > /* VHOST_NET specific defines */ > > > > > > > > /* Attach virtio net ring to a raw socket, or tap device. > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > > index 9e8e004..3b68f9d 100644 > > > > --- a/drivers/vhost/vhost.c > > > > +++ b/drivers/vhost/vhost.c > > > > @@ -917,6 +917,11 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > > > > long r; > > > > int i, fd; > > > > > > > > + if (ioctl == VHOST_GET_MEM_MAX_NREGIONS) { > > > > + r = VHOST_MEMORY_MAX_NREGIONS; > > > > + goto done; > > > > + } > > > > + > > > > /* If you are not the owner, you can become one */ > > > > if (ioctl == VHOST_SET_OWNER) { > > > > r = vhost_dev_set_owner(d); > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/