vm_reserv: clarify reserv_from_object

[dougm]

Summary

vm_reserv_from_page returns an existing reservation, or initializes a successor pointer, or both. If it returns an existing reservation, callers will ignore the successor pointer, initialized or not, so initializing it serves no purpose. So, don't initialize it in that case, and make less ambiguous the comment that describes the function's behavior.

[markj]

Doesn't this leave msucc uninitialized in vm_reserv_from_object()'s callers? I think we can then reach a msucc != NULL test there even if vm_reserv_from_object() returns a non-NULL pointer.

[dougm]

In D49415#1128114, @markj wrote:

Doesn't this leave msucc uninitialized in vm_reserv_from_object()'s callers?

Only if the function returns a non-NULL value.

I think we can then reach a msucc != NULL test there even if vm_reserv_from_object() returns a non-NULL pointer.

I disagree. After each call, an rv != NULL test leads to a block that includes return statements, with no way to avoid encountering one of them.