We never allocate the ceph_buffer and buffer separtely, so use a single
constructor.
Disallow put on NULL buffer; make the caller check.
Signed-off-by: Sage Weil <sage@newdream.net>
struct ceph_buffer is a simple ref-counted buffer. We transparently
choose between kmalloc for small buffers and vmalloc for large ones.
This is currently used only for allocating memory for xattr data.
Signed-off-by: Sage Weil <sage@newdream.net>