On Mon, Jul 4, 2011 at 9:40 PM, Greg KH <greg@xxxxxxxxx> wrote:
> On Mon, Jul 04, 2011 at 06:13:49PM +0530, Amit Nagal wrote:
>> Hi ,
>>
>> if a application is doing read /write I/O with a usb device , in 2
>> different threads in userspace ,
>
> What type of USB device?
Thanx for reply .
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 ?
Regards
Amit Nagal
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