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Mon, 16 Aug 2021 01:39:54 -0700 (PDT) Received: from [192.168.8.102] ([86.32.42.198]) by smtp.gmail.com with ESMTPSA id n2sm4510744edi.32.2021.08.16.01.39.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Aug 2021 01:39:54 -0700 (PDT) To: bongsu.jeon2@gmail.com, shuah@kernel.org Cc: netdev@vger.kernel.org, linux-nfc@lists.01.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Bongsu Jeon References: <20210816040600.175813-1-bongsu.jeon2@gmail.com> <20210816040600.175813-2-bongsu.jeon2@gmail.com> From: Krzysztof Kozlowski Subject: Re: [PATCH net-next 1/3] nfc: Change the virtual NCI device driver to use Wait Queue Message-ID: <47a9321b-c79e-a06e-6575-9321a758dc36@canonical.com> Date: Mon, 16 Aug 2021 10:39:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210816040600.175813-2-bongsu.jeon2@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/08/2021 06:05, bongsu.jeon2@gmail.com wrote: > From: Bongsu Jeon > > In previous version, the user level virtual device application that used > this driver should have the polling scheme to read a NCI frame. > To remove this polling scheme, changed the driver code to use Wait Queue. > Subject - please prefix it with: "nfc: virtual_ncidev: " Also make it simpler (skipping unnecessary words like "change", "device driver"), so: "nfc: virtual_ncidev: use wait queue instead of polling" > Signed-off-by: Bongsu Jeon > --- > drivers/nfc/virtual_ncidev.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c > index 2ee0ec4bb739..1953904176a2 100644 > --- a/drivers/nfc/virtual_ncidev.c > +++ b/drivers/nfc/virtual_ncidev.c > @@ -10,6 +10,7 @@ > #include > #include > #include > +#include > #include > > enum virtual_ncidev_mode { > @@ -27,6 +28,7 @@ enum virtual_ncidev_mode { > NFC_PROTO_ISO15693_MASK) > > static enum virtual_ncidev_mode state; > +static DECLARE_WAIT_QUEUE_HEAD(wq); > static struct miscdevice miscdev; > static struct sk_buff *send_buff; > static struct nci_dev *ndev; > @@ -61,6 +63,7 @@ static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb) > } > send_buff = skb_copy(skb, GFP_KERNEL); > mutex_unlock(&nci_mutex); > + wake_up_interruptible(&wq); > > return 0; > } > @@ -76,12 +79,11 @@ static ssize_t virtual_ncidev_read(struct file *file, char __user *buf, > { > size_t actual_len; > > - mutex_lock(&nci_mutex); > - if (!send_buff) { > - mutex_unlock(&nci_mutex); > + wait_event_interruptible(wq, send_buff); > + if (!send_buff) I think access to send_buff should still be protected by mutex. What happens if you have to readers? > return 0; > - } > > + mutex_lock(&nci_mutex); > actual_len = min_t(size_t, count, send_buff->len); > > if (copy_to_user(buf, send_buff->data, actual_len)) { > Best regards, Krzysztof