Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753279AbbG2O4H (ORCPT ); Wed, 29 Jul 2015 10:56:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43242 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752758AbbG2O4F (ORCPT ); Wed, 29 Jul 2015 10:56:05 -0400 Date: Wed, 29 Jul 2015 17:56:02 +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: <20150729175434-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> <20150729174229-mutt-send-email-mst@redhat.com> <20150729165351.16ae62ff@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150729165351.16ae62ff@nial.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4704 Lines: 113 On Wed, Jul 29, 2015 at 04:53:51PM +0200, Igor Mammedov wrote: > On Wed, 29 Jul 2015 17:43:17 +0300 > "Michael S. Tsirkin" wrote: > > > 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 ... > for most cases it would work but distro doesn't have to mount > sysfs under /sys If it wants to rewrite all userspace, sure it doesn't. > so it adds to app a burden of discovering > where sysfs is mounted and in what module to look for parameter. > > So IMHO, sysfs is more human oriented interface, > while ioctl is more stable API for apps. I don't think that's right. ioctls only make sense for per-fd info. > > > > > > > > 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/