ANDROID: Add ashmem ioctl to return a unique file identifier

This will allow a client program to avoid redundant actions on ashmem
buffers which it has already seen.

Bug: 244233389
Change-Id: Ica57a8842ff163eae5f9eca8141b439091ec0940
Signed-off-by: Mark Fasheh <mfasheh@google.com>
(cherry picked from commit fb15c7c8b02354464e3a1c54d9a1700e3470c7a2)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

Author: Mark Fasheh

drivers/staging/android/ashmem.c

@@ -820,6 +820,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
 static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct ashmem_area *asma = file->private_data;
+	unsigned long ino;
 	long ret = -ENOTTY;
 
 	switch (cmd) {
@@ -863,6 +864,23 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			ashmem_shrink_scan(&ashmem_shrinker, &sc);
 		}
 		break;
+	case ASHMEM_GET_FILE_ID:
+		/* Lock around our check to avoid racing with ashmem_mmap(). */
+		mutex_lock(&ashmem_mutex);
+		if (!asma || !asma->file) {
+			mutex_unlock(&ashmem_mutex);
+			ret = -EINVAL;
+			break;
+		}
+		ino = file_inode(asma->file)->i_ino;
+		mutex_unlock(&ashmem_mutex);
+
+		if (copy_to_user((void __user *)arg, &ino, sizeof(ino))) {
+			ret = -EFAULT;
+			break;
+		}
+		ret = 0;
+		break;
 	}
 
 	return ret;

drivers/staging/android/uapi/ashmem.h

@@ -39,5 +39,6 @@ struct ashmem_pin {
 #define ASHMEM_UNPIN		_IOW(__ASHMEMIOC, 8, struct ashmem_pin)
 #define ASHMEM_GET_PIN_STATUS	_IO(__ASHMEMIOC, 9)
 #define ASHMEM_PURGE_ALL_CACHES	_IO(__ASHMEMIOC, 10)
+#define ASHMEM_GET_FILE_ID		_IOR(__ASHMEMIOC, 11, unsigned long)
 
 #endif	/* _UAPI_LINUX_ASHMEM_H */