On Mon, Nov 11, 2013 at 12:57:47AM -0800, Thomas Hellstrom wrote:Resending since it appears this RFC never got to the dri-devel lkml lists.NAK for struct file. This kind of stuff is for implementing primitives,
In this context, a "doomed" object is an object whose refcount has reached
zero, but that has not yet been freed.
To avoid mutual refcounting vmwgfx need to have a non-refcounted pointer to
a dma-buf in a lookup structure. The pointer is removed in the dma-buf
destructor. To allow lookup-structure private locks we need
get_dma_buf_unless_doomed(). This common refcounting scenario is described
with examples in detail in the kref documentaion.
The solution with local locks is under kref_get_unless_zero().
See also kobject_get_unless_zero() and its commit message.
Since dma-bufs are using the attached file for refcounting,
get_dma_buf_unless_doomed maps directly to a get_file_unless_doomed.
not as a public API.
BTW, as for dmabuf... dma_buf_fd() calling conventions
are seriously misguided - we are trying to transfer the reference we hold
into something (in this case - descriptor table), so the failure exit
should be dropping the reference, not leaving that to caller