qemu-kvm/kvm-Revert-vhost-user-Introduce-nested-event-loop-in-vho.patch

From 0c19fb7c4a22a30830152b224b2e66963f829a7a Mon Sep 17 00:00:00 2001
From: Greg Kurz <groug@kaod.org>
Date: Thu, 19 Jan 2023 18:24:24 +0100
Subject: [PATCH 19/20] Revert "vhost-user: Introduce nested event loop in
 vhost_user_read()"
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RH-Author: Laurent Vivier <lvivier@redhat.com>
RH-MergeRequest: 146: Fix vhost-user with dpdk
RH-Bugzilla: 2155173
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: Greg Kurz (RH) <gkurz@redhat.com>
RH-Acked-by: Eugenio Pérez <eperezma@redhat.com>
RH-Commit: [2/2] 9b67041f92f29f70b7ccb41d8087801e4e4e38af (lvivier/qemu-kvm-centos)

This reverts commit a7f523c7d114d445c5d83aecdba3efc038e5a692.

The nested event loop is broken by design. It's only user was removed.
Drop the code as well so that nobody ever tries to use it again.

I had to fix a couple of trivial conflicts around return values because
of 025faa872bcf ("vhost-user: stick to -errno error return convention").

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20230119172424.478268-3-groug@kaod.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
(cherry picked from commit 4382138f642f69fdbc79ebf4e93d84be8061191f)
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/vhost-user.c | 65 ++++--------------------------------------
 1 file changed, 5 insertions(+), 60 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 0ac00eb901..7cb49c50f9 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -305,19 +305,8 @@ static int vhost_user_read_header(struct vhost_dev *dev, VhostUserMsg *msg)
     return 0;
 }
 
-struct vhost_user_read_cb_data {
-    struct vhost_dev *dev;
-    VhostUserMsg *msg;
-    GMainLoop *loop;
-    int ret;
-};
-
-static gboolean vhost_user_read_cb(void *do_not_use, GIOCondition condition,
-                                   gpointer opaque)
+static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
 {
-    struct vhost_user_read_cb_data *data = opaque;
-    struct vhost_dev *dev = data->dev;
-    VhostUserMsg *msg = data->msg;
     struct vhost_user *u = dev->opaque;
     CharBackend *chr = u->user->chr;
     uint8_t *p = (uint8_t *) msg;
@@ -325,8 +314,7 @@ static gboolean vhost_user_read_cb(void *do_not_use, GIOCondition condition,
 
     r = vhost_user_read_header(dev, msg);
     if (r < 0) {
-        data->ret = r;
-        goto end;
+        return r;
     }
 
     /* validate message size is sane */
@@ -334,8 +322,7 @@ static gboolean vhost_user_read_cb(void *do_not_use, GIOCondition condition,
         error_report("Failed to read msg header."
                 " Size %d exceeds the maximum %zu.", msg->hdr.size,
                 VHOST_USER_PAYLOAD_SIZE);
-        data->ret = -EPROTO;
-        goto end;
+        return -EPROTO;
     }
 
     if (msg->hdr.size) {
@@ -346,53 +333,11 @@ static gboolean vhost_user_read_cb(void *do_not_use, GIOCondition condition,
             int saved_errno = errno;
             error_report("Failed to read msg payload."
                          " Read %d instead of %d.", r, msg->hdr.size);
-            data->ret = r < 0 ? -saved_errno : -EIO;
-            goto end;
+            return r < 0 ? -saved_errno : -EIO;
         }
     }
 
-end:
-    g_main_loop_quit(data->loop);
-    return G_SOURCE_REMOVE;
-}
-
-static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
-{
-    struct vhost_user *u = dev->opaque;
-    CharBackend *chr = u->user->chr;
-    GMainContext *prev_ctxt = chr->chr->gcontext;
-    GMainContext *ctxt = g_main_context_new();
-    GMainLoop *loop = g_main_loop_new(ctxt, FALSE);
-    struct vhost_user_read_cb_data data = {
-        .dev = dev,
-        .loop = loop,
-        .msg = msg,
-        .ret = 0
-    };
-
-    /*
-     * We want to be able to monitor the slave channel fd while waiting
-     * for chr I/O. This requires an event loop, but we can't nest the
-     * one to which chr is currently attached : its fd handlers might not
-     * be prepared for re-entrancy. So we create a new one and switch chr
-     * to use it.
-     */
-    qemu_chr_be_update_read_handlers(chr->chr, ctxt);
-    qemu_chr_fe_add_watch(chr, G_IO_IN | G_IO_HUP, vhost_user_read_cb, &data);
-
-    g_main_loop_run(loop);
-
-    /*
-     * Restore the previous event loop context. This also destroys/recreates
-     * event sources : this guarantees that all pending events in the original
-     * context that have been processed by the nested loop are purged.
-     */
-    qemu_chr_be_update_read_handlers(chr->chr, prev_ctxt);
-
-    g_main_loop_unref(loop);
-    g_main_context_unref(ctxt);
-
-    return data.ret;
+    return 0;
 }
 
 static int process_message_reply(struct vhost_dev *dev,
-- 
2.31.1