[Qemu-devel] [PATCH 3/4] virtio-9p: Wait for 9p operations to complete before migration.

["Benoît Canet" <benoit@irqsave.net>]

The function used to wait is registered as a pre migration flush hook.

The completion status is put in the virtio ring buffer which
will be send to the guest on resume by the viring migration code

This patch is a rewrite from the one written by Aneesh Kumar.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 hw/9pfs/virtio-9p-device.c |    2 ++
 hw/9pfs/virtio-9p.c        |   70 ++++++++++++++++++++++++++++++++++++++++++++
 hw/9pfs/virtio-9p.h        |    2 ++
 3 files changed, 74 insertions(+)

diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index 7d4aefd..02b8630 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -200,6 +200,8 @@ VirtIODevice *virtio_9p_init(DeviceState *dev, V9fsConf *conf)
     V9fsPath path;
     static int virtio_9p_id;
 
+    v9fs_init_migration_helper();
+
     s = (V9fsState *)virtio_common_init("virtio-9p",
                                     VIRTIO_ID_9P,
                                     sizeof(struct virtio_9p_config)+
diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 5cc4c92..3bf3ee4 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -20,11 +20,20 @@
 #include "virtio-9p-coth.h"
 #include "trace.h"
 #include "migration/migration.h"
+#include "migration/migration-flush-hooks.h"
 
 int open_fd_hw;
 int total_open_fd;
 static int open_fd_rc;
 
+typedef struct MigrationHelper {
+    int32_t pending_requests;
+    QemuCond complete;
+    QemuMutex mutex;
+} MigrationHelper;
+
+MigrationHelper *migration;
+
 enum {
     Oread   = 0x00,
     Owrite  = 0x01,
@@ -37,6 +46,62 @@ enum {
     Oappend = 0x80,
 };
 
+static void v9fs_wait_for_requests_drain(void)
+{
+    if (!migration) {
+        return;
+    }
+
+    qemu_mutex_lock(&migration->mutex);
+    while (migration->pending_requests) {
+        /* At this point ticks and vcpus will be stopped so we can safely
+         * release the BQL so pending 9p callbacks will be executed and the
+         * condition signaled.
+         */
+        qemu_mutex_unlock_iothread();
+        qemu_cond_wait(&migration->complete, &migration->mutex);
+        qemu_mutex_lock_iothread();
+    }
+    qemu_mutex_unlock(&migration->mutex);
+}
+
+void v9fs_init_migration_helper(void)
+{
+    if (migration) {
+        return;
+    }
+
+    migration = g_new0(MigrationHelper, 1);
+    qemu_mutex_init(&migration->mutex);
+    qemu_cond_init(&migration->complete);
+    register_migration_flush_hook(v9fs_wait_for_requests_drain);
+}
+
+static void v9fs_inc_pending_requests(void)
+{
+    if (!migration) {
+        return;
+    }
+
+    qemu_mutex_lock(&migration->mutex);
+    migration->pending_requests++;
+    qemu_mutex_unlock(&migration->mutex);
+}
+
+static void v9fs_dec_pending_requests(void)
+{
+    if (!migration) {
+        return;
+    }
+
+    qemu_mutex_lock(&migration->mutex);
+    migration->pending_requests--;
+    if (!migration->pending_requests) {
+        qemu_cond_signal(&migration->complete);
+    }
+    qemu_mutex_unlock(&migration->mutex);
+}
+
 static int omode_to_uflags(int8_t mode)
 {
     int ret = 0;
@@ -637,6 +702,8 @@ static void complete_pdu(V9fsState *s, V9fsPDU *pdu, ssize_t len)
     qemu_co_queue_next(&pdu->complete);
 
     free_pdu(s, pdu);
+
+    v9fs_dec_pending_requests();
 }
 
 static mode_t v9mode_to_mode(uint32_t mode, V9fsString *extension)
@@ -3240,6 +3307,9 @@ static void submit_pdu(V9fsState *s, V9fsPDU *pdu)
     if (is_ro_export(&s->ctx) && !is_read_only_op(pdu)) {
         handler = v9fs_fs_ro;
     }
+
+    v9fs_inc_pending_requests();
+
     co = qemu_coroutine_create(handler);
     qemu_coroutine_enter(co, pdu);
 }
diff --git a/hw/9pfs/virtio-9p.h b/hw/9pfs/virtio-9p.h
index 52b1c69..4d16d46 100644
--- a/hw/9pfs/virtio-9p.h
+++ b/hw/9pfs/virtio-9p.h
@@ -401,4 +401,6 @@ extern int v9fs_name_to_path(V9fsState *s, V9fsPath *dirpath,
 #define pdu_unmarshal(pdu, offset, fmt, args...)  \
     v9fs_unmarshal(pdu->elem.out_sg, pdu->elem.out_num, offset, 1, fmt, ##args)
 
+void v9fs_init_migration_helper(void);
+
 #endif
-- 
1.7.10.4