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Tsirkin" To: Laurent Vivier Subject: Re: [PATCH v2] virtio-rng: return available data with O_NONBLOCK Message-ID: <20200811090814-mutt-send-email-mst@kernel.org> References: <20200715133255.10526-1-mwilck@suse.com> <7cfc4316-922b-8606-72ce-80205ef55572@redhat.com> <7affb721-9686-1262-b7cf-d9681646b602@redhat.com> <810451cf80032d131d5d3feb4fc8300549516f3d.camel@suse.com> <085f699b-e391-7363-b63e-3b11cc04e50d@redhat.com> MIME-Version: 1.0 In-Reply-To: <085f699b-e391-7363-b63e-3b11cc04e50d@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/11 06:40:20 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Amit Shah , Jason Wang , qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Martin Wilck Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Aug 11, 2020 at 03:00:14PM +0200, Laurent Vivier wrote: > No problem. This code is tricky and it took me several months to really > start to understand it ... Oh great, we actually have someone who understands the code! Maybe you can help me understand: virtio_read takes the buf pointer and puts it in the vq. It can then return to caller (e.g. on a signal). Device can meanwhile write into the buffer. It looks like if another call then happens, and that other call uses a different buffer, virtio rng will happily return the data written into the original buf pointer, confusing the caller. Is that right? -- MST