Please describe the problem:
Ideally, after inserting a audio CD, gio will emit a mount-added signal, then it will trigger a greeting dialog to pop up. However, this doesn't happen in my actual case.
After debugging, in autorun_guessed_content_type_callback(), it will go into if(error != NULL) clause to output the above warning message. Ideally, it should go into the else clause. Here the cause is that error != NULL, and the error is a output value of g_mount_guess_content_type_finish.
In the description of  g_mount_guess_content_type_finish, there's the following lines:
* Finishes guessing content types of @mount. If any errors occured
* during the operation, @error will be set to contain the errors and
* %FALSE will be returned. In particular, you may get an 
* %G_IO_ERROR_NOT_SUPPORTED if the mount does not support content 
* guessing.

Before that warning message, nautilus also output another warning message: " WARNING **: Unable to add monitor: Not supported". 

So, is the root cause here that the mount does not support content guessing? 


Steps to reproduce:
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Actual results:


Expected results:


Does this happen every time?


Other information: