nvmed: multiple I/O queue pairs + Set Features / Number of Queues

Replaced single I/O queue pair with dynamic allocation of up to 8 pairs
using NVMe Set Features command (Feature ID 0x07, Number of Queues).

Cross-referenced with Linux 7.1 nvme_set_queue_count() in drivers/nvme/host/core.c.
Controller advertises max SQ/CQ count; driver creates min(requested, allocated, 8)
queue pairs for parallel I/O submission. Each pair gets a unique interrupt vector
(round-robin across 4 MSI-X vectors).

Previous behavior: hardcoded qid=1 only. New behavior: qid 1..N based on
controller capabilities. Improves I/O throughput on multi-core systems
by enabling concurrent command submission across queues.

drivers/storage/nvmed/src/nvme/cmd.rs

@@ -159,4 +159,22 @@ impl NvmeCmd {
             cdw15: 0,
         }
     }
+
+    pub fn set_features_num_queues(cid: u16, nsid: u32, ncqr: u16, nsqr: u16) -> Self {
+        Self {
+            opcode: 9, // Set Features
+            flags: 0,
+            cid,
+            nsid,
+            _rsvd: 0,
+            mptr: 0,
+            dptr: [0, 0],
+            cdw10: 0x07, // Feature ID: Number of Queues
+            cdw11: ((ncqr as u32) << 16) | (nsqr as u32),
+            cdw12: 0,
+            cdw13: 0,
+            cdw14: 0,
+            cdw15: 0,
+        }
+    }
 }

drivers/storage/nvmed/src/nvme/mod.rs

@@ -423,21 +423,36 @@ impl Nvme {
             namespaces.insert(nsid, self.identify_namespace(nsid).await);
         }
 
-        // TODO: Multiple queues
-        let cq = self.create_io_completion_queue(1, Some(0)).await;
-        log::trace!("created compq");
-        let sq = self.create_io_submission_queue(1, 1).await;
-        log::trace!("created subq");
-        self.thread_ctxts
-            .read()
-            .get(&0)
-            .unwrap()
-            .lock()
-            .queues
-            .borrow_mut()
-            .insert(1, (sq, cq));
-        self.sq_ivs.write().insert(1, 0);
-        self.cq_ivs.write().insert(1, 0);
+        // NVMe Set Features / Number of Queues (Feature ID 0x07).
+        // Linux 7.1 reference: drivers/nvme/host/core.c nvme_set_queue_count().
+        // Request max I/O queues from controller, allocate up to
+        // min(requested, allocated, CPU_COUNT) queue pairs.
+        let nvme_queue_count = self
+            .submit_and_complete_admin_command(|cid| {
+                NvmeCmd::set_features_num_queues(cid, 0, 64, 64)
+            })
+            .await;
+        let ncqr = nvme_queue_count.command_specific;
+        let nsqr = ncqr >> 16;
+        let ncqr = ncqr & 0xFFFF;
+        let n_queues = (nsqr.min(ncqr) as usize).min(8).max(1);
+        log::info!("nvmed: controller supports {} SQ / {} CQ, creating {} I/O queue pairs", nsqr, ncqr, n_queues);
+
+        for qid in 1..=n_queues as u16 {
+            let cq = self.create_io_completion_queue(qid, Some((qid - 1) as u16 % 4)).await;
+            let sq = self.create_io_submission_queue(qid, qid).await;
+            log::trace!("nvmed: created I/O queue pair qid={}", qid);
+            self.thread_ctxts
+                .read()
+                .get(&0)
+                .unwrap()
+                .lock()
+                .queues
+                .borrow_mut()
+                .insert(qid, (sq, cq));
+            self.sq_ivs.write().insert(qid, (qid - 1) as u16 % 4);
+            self.cq_ivs.write().insert(qid, (qid - 1) as u16 % 4);
+        }
 
         namespaces
     }