From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation Date: Thu, 06 Sep 2012 11:34:25 +0930 Message-ID: <87k3w7j49i.fsf@rustcorp.com.au> References: <1346680277-5887-1-git-send-email-sjur.brandeland@stericsson.com> <20120903143018.GA5353@redhat.com> <20120903202737.GD6181@redhat.com> <20120904135022.GI9805@redhat.com> <20120904185541.GB3602@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <20120904185541.GB3602@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" , Sjur =?utf-8?Q?Br=C3=A6ndeland?= Cc: Amit Shah , Linus Walleij , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org Ik1pY2hhZWwgUy4gVHNpcmtpbiIgPG1zdEByZWRoYXQuY29tPiB3cml0ZXM6Cj4gT24gVHVlLCBT ZXAgMDQsIDIwMTIgYXQgMDY6NTg6NDdQTSArMDIwMCwgU2p1ciBCcsOmbmRlbGFuZCB3cm90ZToK Pj4gSGkgTWljaGFlbCwKPj4gCj4+ID4gRXhhY3RseS4gVGhvdWdoIGlmIHdlIGp1c3QgZmFpbCBs b2FkIGl0IHdpbGwgYmUgbXVjaCBsZXNzIGNvZGUuCj4+ID4KPj4gPiBHZW5lcmFsbHksIHVzaW5n IGEgZmVhdHVyZSBiaXQgZm9yIHRoaXMgaXMgYSBiaXQgb2YgYSBwcm9ibGVtIHRob3VnaDoKPj4g PiBub3JtYWxseSBkcml2ZXIgaXMgZXhwZWN0ZWQgdG8gYmUgYWJsZSB0byBzaW1wbHkgaWdub3Jl Cj4+ID4gYSBmZWF0dXJlIGJpdC4gSW4gdGhpcyBjYXNlIGRyaXZlciBpcyByZXF1aXJlZCB0bwo+ PiA+IGRvIHNvbWV0aGluZyBzbyBhIGZlYXR1cmUgYml0IGlzIG5vdCBhIGdvb2QgZml0Lgo+PiA+ IEkgYW0gbm90IHN1cmUgd2hhdCB0aGUgcmlnaHQgdGhpbmcgdG8gZG8gaXMuCj4+IAo+PiBJIHNl ZSAtIHNvIGluIG9yZGVyIHRvIGF2b2lkIHRoZSBiaW5kaW5nIGJldHdlZW4gZHJpdmVyIGFuZCBk ZXZpY2UKPj4gdGhlcmUgYXJlIHR3byBvcHRpb25zIEkgZ3Vlc3MuIEVpdGhlciBtYWtlIHZpcnRp b19kZXZfbWF0Y2goKSBvcgo+PiB2aXJ0Y29uc19wcm9iZSgpIGZhaWwuIE5laXRoZXIgb2YgdGhl bSBzZWVtcyBsaWtlIHRoZSBvYnZpb3VzIGNob2ljZS4KPj4gCj4+IE1heWJlIGFkZGluZyBhIGNo ZWNrIGZvciBWSVJUSU9fQ09OU09MRV9GX0RNQV9NRU0gbWF0Y2gKPj4gYmV0d2VlbiBkZXZpY2Ug YW5kIGRyaXZlciBpbiB2aXJ0Y29uc19wcm9iZSgpIGlzIHRoZSBsZXNzZXIgZXZpbD8KPj4gCj4+ IFJlZ2FyZHMsCj4+IFNqdXIKPgo+IEEgc2ltcGxlc3QgdGhpbmcgdG8gZG8gaXMgY2hhbmdlIGRl diBpZC4gcnVzdHk/CgpGb3IgZ2VuZXJpYyB1c2FnZSwgdGhpcyBpcyBjb3JyZWN0LiAgQnV0IG15 IG9waW5pb24gaXMgdGhhdCBmYWxsYmFjayBvbgpmZWF0dXJlIG5vbi1hY2sgaXMgcXVhbGl0eS1v Zi1pbXBsZW1lbnRhdGlvbiBpc3N1ZTogZ3JlYXQgdG8gaGF2ZSwgYnV0CnRoZXJlIGFyZSBjYXNl cyB3aGVyZSB5b3UganVzdCB3YW50IHRvIGZhaWwgd2l0aCAieW91J3JlIHRvbyBvbGQiLgoKQW5k IGluIHRoaXMgY2FzZSwgYW4gb2xkIHN5c3RlbSBzaW1wbHkgd2lsbCBuZXZlciB3b3JrLiAgU28g aXQncyBhCnF1ZXN0aW9uIG9mIGhvdyBncmFjZWZ1bCB0aGUgZmFpbHVyZSBpcy4KCkNhbiB5b3Vy IHVzZXJzcGFjZSBsb2FkZXIgY2FuIHJlZnVzZSB0byBwcm9jZWVkIGlmIHRoZSBkcml2ZXIgZG9l c24ndAphY2sgdGhlIGJpdHM/ICBJZiBzbywgaXQncyBzaW1wbGVyIHRoYW4gYSB3aG9sZSBuZXcg SUQuCgpDaGVlcnMsClJ1c3R5LgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fXwpWaXJ0dWFsaXphdGlvbiBtYWlsaW5nIGxpc3QKVmlydHVhbGl6YXRpb25AbGlz dHMubGludXgtZm91bmRhdGlvbi5vcmcKaHR0cHM6Ly9saXN0cy5saW51eGZvdW5kYXRpb24ub3Jn L21haWxtYW4vbGlzdGluZm8vdmlydHVhbGl6YXRpb24= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755343Ab2IFDA4 (ORCPT ); Wed, 5 Sep 2012 23:00:56 -0400 Received: from ozlabs.org ([203.10.76.45]:55569 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754161Ab2IFDAx convert rfc822-to-8bit (ORCPT ); Wed, 5 Sep 2012 23:00:53 -0400 From: Rusty Russell To: "Michael S. Tsirkin" , Sjur =?utf-8?Q?Br=C3=A6ndeland?= Cc: Amit Shah , linux-kernel@vger.kernel.org, Ohad Ben-Cohen , Linus Walleij , virtualization@lists.linux-foundation.org Subject: Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation In-Reply-To: <20120904185541.GB3602@redhat.com> References: <1346680277-5887-1-git-send-email-sjur.brandeland@stericsson.com> <20120903143018.GA5353@redhat.com> <20120903202737.GD6181@redhat.com> <20120904135022.GI9805@redhat.com> <20120904185541.GB3602@redhat.com> User-Agent: Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Thu, 06 Sep 2012 11:34:25 +0930 Message-ID: <87k3w7j49i.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Michael S. Tsirkin" writes: > On Tue, Sep 04, 2012 at 06:58:47PM +0200, Sjur Brændeland wrote: >> Hi Michael, >> >> > Exactly. Though if we just fail load it will be much less code. >> > >> > Generally, using a feature bit for this is a bit of a problem though: >> > normally driver is expected to be able to simply ignore >> > a feature bit. In this case driver is required to >> > do something so a feature bit is not a good fit. >> > I am not sure what the right thing to do is. >> >> I see - so in order to avoid the binding between driver and device >> there are two options I guess. Either make virtio_dev_match() or >> virtcons_probe() fail. Neither of them seems like the obvious choice. >> >> Maybe adding a check for VIRTIO_CONSOLE_F_DMA_MEM match >> between device and driver in virtcons_probe() is the lesser evil? >> >> Regards, >> Sjur > > A simplest thing to do is change dev id. rusty? For generic usage, this is correct. But my opinion is that fallback on feature non-ack is quality-of-implementation issue: great to have, but there are cases where you just want to fail with "you're too old". And in this case, an old system simply will never work. So it's a question of how graceful the failure is. Can your userspace loader can refuse to proceed if the driver doesn't ack the bits? If so, it's simpler than a whole new ID. Cheers, Rusty.