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[104.57.184.186]) by smtp.gmail.com with ESMTPSA id v17sm3497202ott.7.2021.01.25.07.31.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Jan 2021 07:31:04 -0800 (PST) Date: Mon, 25 Jan 2021 09:31:02 -0600 From: Bjorn Andersson To: Arnaud POULIQUEN Cc: Mathieu Poirier , Arnaud POULIQUEN - foss , Ohad Ben-Cohen , "linux-stm32@st-md-mailman.stormreply.com" , "linux-remoteproc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [Linux-stm32] [PATCH] rpmsg: char: return an error if device already open Message-ID: References: <20210106133714.9984-1-arnaud.pouliquen@foss.st.com> <20210114190543.GB255481@xps15> <6de9ff8f-0be1-387a-df7e-7d77dd859513@st.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6de9ff8f-0be1-387a-df7e-7d77dd859513@st.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 15 Jan 03:13 CST 2021, Arnaud POULIQUEN wrote: > Hi Mathieu, > > > On 1/14/21 8:05 PM, Mathieu Poirier wrote: > > On Wed, Jan 06, 2021 at 02:37:14PM +0100, Arnaud Pouliquen wrote: > >> The rpmsg_create_ept function is invoked when the device is opened. > >> As only one endpoint must be created per device. It is not > >> possible to open the same device twice. > >> The fix consists in returning -EBUSY when device is already > >> opened. > >> > >> Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface") > >> Signed-off-by: Arnaud Pouliquen > >> --- > >> drivers/rpmsg/rpmsg_char.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c > >> index 4bbbacdbf3bb..360a1ab0a9c4 100644 > >> --- a/drivers/rpmsg/rpmsg_char.c > >> +++ b/drivers/rpmsg/rpmsg_char.c > >> @@ -127,6 +127,9 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp) > >> struct rpmsg_device *rpdev = eptdev->rpdev; > >> struct device *dev = &eptdev->dev; > >> > >> + if (eptdev->ept) > >> + return -EBUSY; > >> + > > > > I rarely had to work so hard to review a 2 line patch... > > That means that my commit description was not enough explicit... > > > > > As far as I can tell the actual code is doing the right thing. If user space is > > trying to open the same eptdev more than once function rpmsg_create_ept() should > > complain and the operation denied, wich is what the current code is doing. > > > > There is currently two customers for this API - SMD and GLINK. The SMD code is > > quite clear that if the channel is already open, the operation will be > > denied [1]. The GLINK code isn't as clear but the fact that it returns NULL on > > error conditions [2] is a good indication that things are working the same way. > > > > What kind of use case are you looking to address? Is there any way you can use > > rpdev->ops->create_ept() as it is currently done? > > This patch was part of the IOCTL rpmsg series. I sent it separately at Bjorn's > request [1]. > I apparently didn't spend as much effort as Mathieu thinking about the details. I do believe that he's right, at least both GLINK and SMD _should_ return -EBUSY if we try to open an already open channel - either because the kernel has bound a driver to the channel or because rpmsg_char already has it opened. > I detect the issue using the RPMSG_ADDR_ANY for the source address when tested > it with the rpmsf_virtio bus. In this case at each sys open of the device, a new > endpoint is created because a new source address is allocated. > In SMD and GLINK channels are identified solely by their name and hence it's not possible to have duplicates. As this isn't the case for virtio I didn't have any objections to it and that's why I asked you to resend it separately. But in line with GLINK/SMD, what would the expected behavior be if I with the virtio backend open a rpmsg_char which is already bound to a kernel driver? Do you think we should get another "channel" or do you think the virtio driver should detect this and return -EBUSY? (I.e. render this patch unnecessary) Regards, Bjorn > [1]https://patchwork.kernel.org/project/linux-remoteproc/patch/20201222105726.16906-11-arnaud.pouliquen@foss.st.com/ > > Thanks, > Arnaud > > > > > Thanks, > > Mathieu > > > > [1]. https://elixir.bootlin.com/linux/v5.11-rc3/source/drivers/rpmsg/qcom_smd.c#L920 > > [2]. https://elixir.bootlin.com/linux/v5.11-rc3/source/drivers/rpmsg/qcom_glink_native.c#L1149 > > > >> get_device(dev); > >> > >> ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo); > >> -- > >> 2.17.1 > >> > > _______________________________________________ > > Linux-stm32 mailing list > > Linux-stm32@st-md-mailman.stormreply.com > > https://st-md-mailman.stormreply.com/mailman/listinfo/linux-stm32 > >