From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-2393-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [66.179.20.138]) by lists.oasis-open.org (Postfix) with ESMTP id 4BB7758192D3 for ; Thu, 13 Jul 2017 01:44:00 -0700 (PDT) Message-ID: <59673365.7080408@intel.com> Date: Thu, 13 Jul 2017 16:46:29 +0800 From: Wei Wang MIME-Version: 1.0 References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-9-git-send-email-wei.w.wang@intel.com> <20170713032207-mutt-send-email-mst@kernel.org> In-Reply-To: <20170713032207-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: [virtio-dev] Re: [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com List-ID: On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote: > On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote: >> Add a new vq, cmdq, to handle requests between the device and driver. >> >> This patch implements two commands sent from the device and handled in >> the driver. >> 1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report >> the guest memory statistics to the host. The stats_vq mechanism is not >> used when the cmdq mechanism is enabled. >> 2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to >> report the guest unused pages to the host. >> >> Since now we have a vq to handle multiple commands, we need to keep only >> one vq operation at a time. Here, we change the existing START_USE() >> and END_USE() to lock on each vq operation. >> >> Signed-off-by: Wei Wang >> Signed-off-by: Liang Li >> --- >> drivers/virtio/virtio_balloon.c | 245 ++++++++++++++++++++++++++++++++++-- >> drivers/virtio/virtio_ring.c | 25 +++- >> include/linux/virtio.h | 2 + >> include/uapi/linux/virtio_balloon.h | 10 ++ >> 4 files changed, 265 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index aa4e7ec..ae91fbf 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt; >> >> struct virtio_balloon { >> struct virtio_device *vdev; >> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; >> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq; >> >> /* The balloon servicing is delegated to a freezable workqueue. */ >> struct work_struct update_balloon_stats_work; >> struct work_struct update_balloon_size_work; >> + struct work_struct cmdq_handle_work; >> >> /* Prevent updating balloon when it is being canceled. */ >> spinlock_t stop_update_lock; >> @@ -90,6 +91,12 @@ struct virtio_balloon { >> /* Memory statistics */ >> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; >> >> + /* Cmdq msg buffer for memory statistics */ >> + struct virtio_balloon_cmdq_hdr cmdq_stats_hdr; >> + >> + /* Cmdq msg buffer for reporting ununsed pages */ >> + struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr; >> + >> /* To register callback in oom notifier call chain */ >> struct notifier_block nb; >> }; >> @@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work) >> queue_work(system_freezable_wq, work); >> } >> >> +static unsigned int cmdq_hdr_add(struct virtqueue *vq, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + bool in) >> +{ >> + unsigned int id = VIRTQUEUE_DESC_ID_INIT; >> + uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr); >> + >> + virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in); >> + >> + /* Deliver the hdr for the host to send commands. */ >> + if (in) { >> + hdr->flags = 0; >> + virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL); >> + virtqueue_kick(vq); >> + } >> + >> + return id; >> +} >> + >> +static void cmdq_add_chain_desc(struct virtio_balloon *vb, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + uint64_t addr, >> + uint32_t len, >> + unsigned int *head_id, >> + unsigned int *prev_id) >> +{ >> +retry: >> + if (*head_id == VIRTQUEUE_DESC_ID_INIT) { >> + *head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0); >> + *prev_id = *head_id; >> + } >> + >> + virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0); >> + if (*head_id == *prev_id) { > That's an ugly way to detect ring full. It's actually not detecting ring full. I will call it tail_id, instead of prev_id. So, *head_id == *tail_id is the case that the first desc was just added by virtqueue_add_chain_desc(). Best, Wei --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Date: Thu, 13 Jul 2017 16:46:29 +0800 Message-ID: <59673365.7080408@intel.com> References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-9-git-send-email-wei.w.wang@intel.com> <20170713032207-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com To: "Michael S. Tsirkin" Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20170713032207-mutt-send-email-mst@kernel.org> List-Id: kvm.vger.kernel.org On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote: > On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote: >> Add a new vq, cmdq, to handle requests between the device and driver. >> >> This patch implements two commands sent from the device and handled in >> the driver. >> 1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report >> the guest memory statistics to the host. The stats_vq mechanism is not >> used when the cmdq mechanism is enabled. >> 2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to >> report the guest unused pages to the host. >> >> Since now we have a vq to handle multiple commands, we need to keep only >> one vq operation at a time. Here, we change the existing START_USE() >> and END_USE() to lock on each vq operation. >> >> Signed-off-by: Wei Wang >> Signed-off-by: Liang Li >> --- >> drivers/virtio/virtio_balloon.c | 245 ++++++++++++++++++++++++++++++++++-- >> drivers/virtio/virtio_ring.c | 25 +++- >> include/linux/virtio.h | 2 + >> include/uapi/linux/virtio_balloon.h | 10 ++ >> 4 files changed, 265 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index aa4e7ec..ae91fbf 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt; >> >> struct virtio_balloon { >> struct virtio_device *vdev; >> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; >> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq; >> >> /* The balloon servicing is delegated to a freezable workqueue. */ >> struct work_struct update_balloon_stats_work; >> struct work_struct update_balloon_size_work; >> + struct work_struct cmdq_handle_work; >> >> /* Prevent updating balloon when it is being canceled. */ >> spinlock_t stop_update_lock; >> @@ -90,6 +91,12 @@ struct virtio_balloon { >> /* Memory statistics */ >> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; >> >> + /* Cmdq msg buffer for memory statistics */ >> + struct virtio_balloon_cmdq_hdr cmdq_stats_hdr; >> + >> + /* Cmdq msg buffer for reporting ununsed pages */ >> + struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr; >> + >> /* To register callback in oom notifier call chain */ >> struct notifier_block nb; >> }; >> @@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work) >> queue_work(system_freezable_wq, work); >> } >> >> +static unsigned int cmdq_hdr_add(struct virtqueue *vq, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + bool in) >> +{ >> + unsigned int id = VIRTQUEUE_DESC_ID_INIT; >> + uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr); >> + >> + virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in); >> + >> + /* Deliver the hdr for the host to send commands. */ >> + if (in) { >> + hdr->flags = 0; >> + virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL); >> + virtqueue_kick(vq); >> + } >> + >> + return id; >> +} >> + >> +static void cmdq_add_chain_desc(struct virtio_balloon *vb, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + uint64_t addr, >> + uint32_t len, >> + unsigned int *head_id, >> + unsigned int *prev_id) >> +{ >> +retry: >> + if (*head_id == VIRTQUEUE_DESC_ID_INIT) { >> + *head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0); >> + *prev_id = *head_id; >> + } >> + >> + virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0); >> + if (*head_id == *prev_id) { > That's an ugly way to detect ring full. It's actually not detecting ring full. I will call it tail_id, instead of prev_id. So, *head_id == *tail_id is the case that the first desc was just added by virtqueue_add_chain_desc(). Best, Wei From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id C9464440874 for ; Thu, 13 Jul 2017 04:44:01 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id p10so50841292pgr.6 for ; Thu, 13 Jul 2017 01:44:01 -0700 (PDT) Received: from mga11.intel.com (mga11.intel.com. [192.55.52.93]) by mx.google.com with ESMTPS id j130si3779551pgc.387.2017.07.13.01.43.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jul 2017 01:44:00 -0700 (PDT) Message-ID: <59673365.7080408@intel.com> Date: Thu, 13 Jul 2017 16:46:29 +0800 From: Wei Wang MIME-Version: 1.0 Subject: Re: [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-9-git-send-email-wei.w.wang@intel.com> <20170713032207-mutt-send-email-mst@kernel.org> In-Reply-To: <20170713032207-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote: > On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote: >> Add a new vq, cmdq, to handle requests between the device and driver. >> >> This patch implements two commands sent from the device and handled in >> the driver. >> 1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report >> the guest memory statistics to the host. The stats_vq mechanism is not >> used when the cmdq mechanism is enabled. >> 2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to >> report the guest unused pages to the host. >> >> Since now we have a vq to handle multiple commands, we need to keep only >> one vq operation at a time. Here, we change the existing START_USE() >> and END_USE() to lock on each vq operation. >> >> Signed-off-by: Wei Wang >> Signed-off-by: Liang Li >> --- >> drivers/virtio/virtio_balloon.c | 245 ++++++++++++++++++++++++++++++++++-- >> drivers/virtio/virtio_ring.c | 25 +++- >> include/linux/virtio.h | 2 + >> include/uapi/linux/virtio_balloon.h | 10 ++ >> 4 files changed, 265 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index aa4e7ec..ae91fbf 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt; >> >> struct virtio_balloon { >> struct virtio_device *vdev; >> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; >> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq; >> >> /* The balloon servicing is delegated to a freezable workqueue. */ >> struct work_struct update_balloon_stats_work; >> struct work_struct update_balloon_size_work; >> + struct work_struct cmdq_handle_work; >> >> /* Prevent updating balloon when it is being canceled. */ >> spinlock_t stop_update_lock; >> @@ -90,6 +91,12 @@ struct virtio_balloon { >> /* Memory statistics */ >> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; >> >> + /* Cmdq msg buffer for memory statistics */ >> + struct virtio_balloon_cmdq_hdr cmdq_stats_hdr; >> + >> + /* Cmdq msg buffer for reporting ununsed pages */ >> + struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr; >> + >> /* To register callback in oom notifier call chain */ >> struct notifier_block nb; >> }; >> @@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work) >> queue_work(system_freezable_wq, work); >> } >> >> +static unsigned int cmdq_hdr_add(struct virtqueue *vq, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + bool in) >> +{ >> + unsigned int id = VIRTQUEUE_DESC_ID_INIT; >> + uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr); >> + >> + virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in); >> + >> + /* Deliver the hdr for the host to send commands. */ >> + if (in) { >> + hdr->flags = 0; >> + virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL); >> + virtqueue_kick(vq); >> + } >> + >> + return id; >> +} >> + >> +static void cmdq_add_chain_desc(struct virtio_balloon *vb, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + uint64_t addr, >> + uint32_t len, >> + unsigned int *head_id, >> + unsigned int *prev_id) >> +{ >> +retry: >> + if (*head_id == VIRTQUEUE_DESC_ID_INIT) { >> + *head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0); >> + *prev_id = *head_id; >> + } >> + >> + virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0); >> + if (*head_id == *prev_id) { > That's an ugly way to detect ring full. It's actually not detecting ring full. I will call it tail_id, instead of prev_id. So, *head_id == *tail_id is the case that the first desc was just added by virtqueue_add_chain_desc(). Best, Wei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34803) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVZj9-0004VL-PK for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:44:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVZj6-0001vZ-K4 for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:44:03 -0400 Received: from mga05.intel.com ([192.55.52.43]:41494) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVZj6-0001v2-AX for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:44:00 -0400 Message-ID: <59673365.7080408@intel.com> Date: Thu, 13 Jul 2017 16:46:29 +0800 From: Wei Wang MIME-Version: 1.0 References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-9-git-send-email-wei.w.wang@intel.com> <20170713032207-mutt-send-email-mst@kernel.org> In-Reply-To: <20170713032207-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote: > On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote: >> Add a new vq, cmdq, to handle requests between the device and driver. >> >> This patch implements two commands sent from the device and handled in >> the driver. >> 1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report >> the guest memory statistics to the host. The stats_vq mechanism is not >> used when the cmdq mechanism is enabled. >> 2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to >> report the guest unused pages to the host. >> >> Since now we have a vq to handle multiple commands, we need to keep only >> one vq operation at a time. Here, we change the existing START_USE() >> and END_USE() to lock on each vq operation. >> >> Signed-off-by: Wei Wang >> Signed-off-by: Liang Li >> --- >> drivers/virtio/virtio_balloon.c | 245 ++++++++++++++++++++++++++++++++++-- >> drivers/virtio/virtio_ring.c | 25 +++- >> include/linux/virtio.h | 2 + >> include/uapi/linux/virtio_balloon.h | 10 ++ >> 4 files changed, 265 insertions(+), 17 deletions(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index aa4e7ec..ae91fbf 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt; >> >> struct virtio_balloon { >> struct virtio_device *vdev; >> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; >> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq; >> >> /* The balloon servicing is delegated to a freezable workqueue. */ >> struct work_struct update_balloon_stats_work; >> struct work_struct update_balloon_size_work; >> + struct work_struct cmdq_handle_work; >> >> /* Prevent updating balloon when it is being canceled. */ >> spinlock_t stop_update_lock; >> @@ -90,6 +91,12 @@ struct virtio_balloon { >> /* Memory statistics */ >> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; >> >> + /* Cmdq msg buffer for memory statistics */ >> + struct virtio_balloon_cmdq_hdr cmdq_stats_hdr; >> + >> + /* Cmdq msg buffer for reporting ununsed pages */ >> + struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr; >> + >> /* To register callback in oom notifier call chain */ >> struct notifier_block nb; >> }; >> @@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work) >> queue_work(system_freezable_wq, work); >> } >> >> +static unsigned int cmdq_hdr_add(struct virtqueue *vq, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + bool in) >> +{ >> + unsigned int id = VIRTQUEUE_DESC_ID_INIT; >> + uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr); >> + >> + virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in); >> + >> + /* Deliver the hdr for the host to send commands. */ >> + if (in) { >> + hdr->flags = 0; >> + virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL); >> + virtqueue_kick(vq); >> + } >> + >> + return id; >> +} >> + >> +static void cmdq_add_chain_desc(struct virtio_balloon *vb, >> + struct virtio_balloon_cmdq_hdr *hdr, >> + uint64_t addr, >> + uint32_t len, >> + unsigned int *head_id, >> + unsigned int *prev_id) >> +{ >> +retry: >> + if (*head_id == VIRTQUEUE_DESC_ID_INIT) { >> + *head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0); >> + *prev_id = *head_id; >> + } >> + >> + virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0); >> + if (*head_id == *prev_id) { > That's an ugly way to detect ring full. It's actually not detecting ring full. I will call it tail_id, instead of prev_id. So, *head_id == *tail_id is the case that the first desc was just added by virtqueue_add_chain_desc(). Best, Wei