ashmem: Implement read(2) in ashmem driver

Signed-off-by: Bjorn Bringert <bringert@android.com>
[jstultz: Tweaked commit subject]
CC: Brian Swetland <swetland@google.com>
CC: Colin Cross <ccross@android.com>
CC: Arve Hjønnevåg <arve@android.com>
CC: Dima Zavin <dima@android.com>
CC: Robert Love <rlove@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/android/ashmem.c

@@ -211,6 +211,32 @@ static int ashmem_release(struct inode *ignored, struct file *file)
 	return 0;
 }
 
+static ssize_t ashmem_read(struct file *file, char __user *buf,
+			   size_t len, loff_t *pos)
+{
+	struct ashmem_area *asma = file->private_data;
+	int ret = 0;
+
+	mutex_lock(&ashmem_mutex);
+
+	/* If size is not set, or set to 0, always return EOF. */
+	if (asma->size == 0) {
+		goto out;
+        }
+
+	if (!asma->file) {
+		ret = -EBADF;
+		goto out;
+	}
+
+	ret = asma->file->f_op->read(asma->file, buf, len, pos);
+
+out:
+	mutex_unlock(&ashmem_mutex);
+	return ret;
+}
+
+
 static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct ashmem_area *asma = file->private_data;
@@ -612,6 +638,7 @@ static struct file_operations ashmem_fops = {
 	.owner = THIS_MODULE,
 	.open = ashmem_open,
 	.release = ashmem_release,
+        .read = ashmem_read,
 	.mmap = ashmem_mmap,
 	.unlocked_ioctl = ashmem_ioctl,
 	.compat_ioctl = ashmem_ioctl,