libvduse: Add support for reconnecting

To support reconnecting after restart or crash, VDUSE backend
might need to resubmit inflight I/Os. This stores the metadata
such as the index of inflight I/O's descriptors to a shm file so
that VDUSE backend can restore them during reconnecting.

Signed-off-by: Xie Yongji <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>

Author: YongjiXie

block/export/vduse-blk.c

@@ -30,6 +30,7 @@ typedef struct VduseBlkExport {
     VirtioBlkHandler handler;
     VduseDev *dev;
     uint16_t num_queues;
+    char *recon_file;
     unsigned int inflight;
 } VduseBlkExport;
 
@@ -125,6 +126,8 @@ static void vduse_blk_enable_queue(VduseDev *dev, VduseVirtq *vq)
 
     aio_set_fd_handler(vblk_exp->export.ctx, vduse_queue_get_fd(vq),
                        true, on_vduse_vq_kick, NULL, NULL, NULL, vq);
+    /* Make sure we don't miss any kick afer reconnecting */
+    eventfd_write(vduse_queue_get_fd(vq), 1);
 }
 
 static void vduse_blk_disable_queue(VduseDev *dev, VduseVirtq *vq)
@@ -306,6 +309,15 @@ static int vduse_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
         return -ENOMEM;
     }
 
+    vblk_exp->recon_file = g_strdup_printf("%s/vduse-blk-%s",
+                                           g_get_tmp_dir(), exp->id);
+    if (vduse_set_reconnect_log_file(vblk_exp->dev, vblk_exp->recon_file)) {
+        error_setg(errp, "failed to set reconnect log file");
+        vduse_dev_destroy(vblk_exp->dev);
+        g_free(vblk_exp->recon_file);
+        return -EINVAL;
+    }
+
     for (i = 0; i < num_queues; i++) {
         vduse_dev_setup_queue(vblk_exp->dev, i, queue_size);
     }
@@ -324,11 +336,16 @@ static int vduse_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
 static void vduse_blk_exp_delete(BlockExport *exp)
 {
     VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
+    int ret;
 
     blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
                                     vblk_exp);
     blk_set_dev_ops(exp->blk, NULL, NULL);
-    vduse_dev_destroy(vblk_exp->dev);
+    ret = vduse_dev_destroy(vblk_exp->dev);
+    if (ret != -EBUSY) {
+        unlink(vblk_exp->recon_file);
+    }
+    g_free(vblk_exp->recon_file);
 }
 
 static void vduse_blk_exp_request_shutdown(BlockExport *exp)