Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752673AbbG2OnV (ORCPT ); Wed, 29 Jul 2015 10:43:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52898 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750814AbbG2OnU (ORCPT ); Wed, 29 Jul 2015 10:43:20 -0400 Date: Wed, 29 Jul 2015 17:43:17 +0300 From: "Michael S. Tsirkin" To: Igor Mammedov Cc: linux-kernel@vger.kernel.org, pbonzini@redhat.com, kvm@vger.kernel.org Subject: Re: [PATCH 1/2] vhost: add ioctl to query nregions upper limit Message-ID: <20150729174229-mutt-send-email-mst@redhat.com> References: <1438180163-275465-1-git-send-email-imammedo@redhat.com> <1438180163-275465-2-git-send-email-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438180163-275465-2-git-send-email-imammedo@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3772 Lines: 96 On Wed, Jul 29, 2015 at 04:29:22PM +0200, Igor Mammedov wrote: > From: "Michael S. Tsirkin" > > 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. What's wrong with reading the module parameter value? It's there in sysfs ... > > Signed-off-by: Michael S. Tsirkin > Signed-off-by: Igor Mammedov > --- > drivers/vhost/vhost.c | 7 ++++++- > include/uapi/linux/vhost.h | 17 ++++++++++++++++- > 2 files changed, 22 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index eec2f11..76dc0cf 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -30,7 +30,7 @@ > > #include "vhost.h" > > -static ushort max_mem_regions = 64; > +static ushort max_mem_regions = VHOST_MEM_MAX_NREGIONS_DEFAULT; > module_param(max_mem_regions, ushort, 0444); > MODULE_PARM_DESC(max_mem_regions, > "Maximum number of memory regions in memory map. (default: 64)"); > @@ -944,6 +944,11 @@ 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 = max_mem_regions; > + goto done; > + } > + > /* If you are not the owner, you can become one */ > if (ioctl == VHOST_SET_OWNER) { > r = vhost_dev_set_owner(d); > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index ab373191..2511954 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 > +/* 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 > + > /* VHOST_NET specific defines */ > > /* Attach virtio net ring to a raw socket, or tap device. > -- > 1.8.3.1 -- 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/