On Tue, 5 Jul 2011, Amit Nagal wrote:
> i am using USB hid interface and using USBHID driver with hid-raw
> device interface .
>
> Actually i have 2 threads in userspace app : one for read and another
> one for write .
>
> my problem is like this :
> In case of usb disconnect , if read() returns first with error and
> application calls close() in read thread itself in userspace , while
> write() is still in progress() in usb driver in a separate thread ,
> is this ok and safe ?
>
> or shall the application be designed such that both until read and
> write return with error , it should not call close in userspace ?
>
> Also to test this , i applied a 10 seconds delay at the end of
> hidraw_read() function in hidraw driver like :
>
> static ssize_t hidraw_read(struct file *file, char __user *buffer,
> size_t count, loff_t *ppos)
> {
> ............................................
> /********************* test block starts */
>
> printk(KERN_EMERG "[%s] - sleep start\n" , __func__);
> mdelay(10000); /* 10s delay */
> printk(KERN_EMERG "[%s] - sleep end\n" , __func__);
>
> /***************** test block ends */
>
> mutex_unlock(&list->read_mutex);
> return ret;
> }
>
> now while hidraw_read is executing 10s delay , i disconnects usb
> device , calls close(fd) .
> i observed , while close(fd) returns with 0 successfully immediately
> , usb driver release() function corresponding to close() was called
> only when hidraw_read returns after completing delay which is approx
> 9s later calling to close() in userspace .
>
> so do the usb-core layers or VFS layers maintains some locks that take
> care that if read / write is in progress
> and application calls close() , corresponding release() method in usb
> driver will be called only upon completion
> of all read / writes ?
The USB layer does not maintain any such locks. The VFS layer probably
does, but to be certain you'd have to ask someone who is more familiar
with it. The linux-usb mailing list isn't a good place for VFS
questions.
Alan Stern
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