USB: CDC WDM driver doesn't support non-blocking reads

support for O_NONBLOCK in read and write path
by simply not waiting for data in read or availability
of the write urb in write but returning -EAGAIN

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 24 insertions, 6 deletions

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 8c64c018b676..3e564bfe17d1 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -313,8 +313,13 @@ static ssize_t wdm_write
         r = usb_autopm_get_interface(desc->intf);
         if (r < 0)
                 goto outnp;
-        r = wait_event_interruptible(desc->wait, !test_bit(WDM_IN_USE,
-                                                           &desc->flags));
+
+        if (!file->f_flags && O_NONBLOCK)
+                r = wait_event_interruptible(desc->wait, !test_bit(WDM_IN_USE,
+                                                                &desc->flags));
+        else
+                if (test_bit(WDM_IN_USE, &desc->flags))
+                        r = -EAGAIN;
         if (r < 0)
                 goto out;
 
@@ -377,7 +382,7 @@ outnl:
 static ssize_t wdm_read
 (struct file *file, char __user *buffer, size_t count, loff_t *ppos)
 {
-        int rv, cntr;
+        int rv, cntr = 0;
         int i = 0;
         struct wdm_device *desc = file->private_data;
 
@@ -389,10 +394,23 @@ static ssize_t wdm_read
         if (desc->length == 0) {
                 desc->read = 0;
 retry:
+                if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
+                        rv = -ENODEV;
+                        goto err;
+                }
                 i++;
-                rv = wait_event_interruptible(desc->wait,
-                                              test_bit(WDM_READ, &desc->flags));
+                if (file->f_flags & O_NONBLOCK) {
+                        if (!test_bit(WDM_READ, &desc->flags)) {
+                                rv = cntr ? cntr : -EAGAIN;
+                                goto err;
+                        }
+                        rv = 0;
+                } else {
+                        rv = wait_event_interruptible(desc->wait,
+                                test_bit(WDM_READ, &desc->flags));
+                }
 
+                /* may have happened while we slept */
                 if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
                         rv = -ENODEV;
                         goto err;
@@ -448,7 +466,7 @@ retry:
 
 err:
         mutex_unlock(&desc->rlock);
-        if (rv < 0)
+        if (rv < 0 && rv != -EAGAIN)
                 dev_err(&desc->intf->dev, "wdm_read: exit error\n");
         return rv;
 }