________________________________________ 发件人: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 发送时间: 2021年3月1日 16:32 收件人: Zhang, Qiang 抄送: zaitcev@xxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx 主题: Re: 回复: [PATCH] USB: usblp: Add device status detection in usblp_poll() [Please note: This e-mail is from an EXTERNAL e-mail address] On Mon, Mar 01, 2021 at 08:26:22AM +0000, Zhang, Qiang wrote: > > > ________________________________________ > 发件人: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> > 发送时间: 2021年3月1日 16:00 > 收件人: Zhang, Qiang > 抄送: zaitcev@xxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx > 主题: Re: [PATCH] USB: usblp: Add device status detection in usblp_poll() > > [Please note: This e-mail is from an EXTERNAL e-mail address] > > On Mon, Mar 01, 2021 at 12:03:00PM +0800, qiang.zhang@xxxxxxxxxxxxx wrote: > > From: Zqiang <qiang.zhang@xxxxxxxxxxxxx> > > > > If usblp device has been disconnected, direct return > > 'EPOLLHUP | EPOLLERR' in usblp_poll(). > > > >Why? What problem are you solving here? Is this fixing an >older > >commit, if so, what one? > > > > There is not need fix older commit. > After the device is disconnected, if the userspace call >poll/select() function, will block and never be awakened . > >If the device is disconnected, how can the file be opened at >all? >Shouldn't it have been torn down already? If the device disconnect happen after the file be opend, and then we call poll/select() will always blocked. Also before we operate the device, we need to judge the state of the device. If it is disconnected, there is no need for subsequent operation . > >And now you are holding a lock across some poll_wait() calls, >is that >going to cause problems? The 'usblp->present' is portect by 'usblp->mut', when devices disconnect, will acquire 'usblp->mut', and set 'usblp->present' zero. Thanks Qiang > >thanks, > >greg k-h
