vhost_user: Add support for GET_MAX_MEM_SLOTS

Add the support for GET_MAX_MEM_SLOTS command. This requests the
vhost-user backend to provide the maximum amount of memory slots
that can be supported.

It is only available if the protocol feature
VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS has been negotiated.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/vhost_user/master.rs b/src/vhost_user/master.rs
index f9da535..a721355 100644
--- a/src/vhost_user/master.rs
+++ b/src/vhost_user/master.rs
@@ -50,6 +50,9 @@ pub trait VhostUserMaster: VhostBackend {
 
     /// Setup slave communication channel.
     fn set_slave_request_fd(&mut self, fd: RawFd) -> Result<()>;
+
+    /// Query the maximum amount of memory slots supported by the backend.
+    fn get_max_mem_slots(&mut self) -> Result<u64>;
 }
 
 fn error_code<T>(err: VhostUserError) -> Result<T> {
@@ -435,6 +438,19 @@ impl VhostUserMaster for Master {
         node.send_request_header(MasterReq::SET_SLAVE_REQ_FD, Some(&fds))?;
         Ok(())
     }
+
+    fn get_max_mem_slots(&mut self) -> Result<u64> {
+        let mut node = self.node();
+        if node.acked_protocol_features & VhostUserProtocolFeatures::CONFIGURE_MEM_SLOTS.bits() == 0
+        {
+            return error_code(VhostUserError::InvalidOperation);
+        }
+
+        let hdr = node.send_request_header(MasterReq::GET_MAX_MEM_SLOTS, None)?;
+        let val = node.recv_reply::<VhostUserU64>(&hdr)?;
+
+        Ok(val.value)
+    }
 }
 
 impl AsRawFd for Master {