[PATCH 2/5] migration: Add generic memfd channel helpers

Add helpers for creating an outgoing memfd-backed migration channel and for
wrapping an existing memfd fd as an incoming migration channel. The
outgoing helper can optionally duplicate the memfd fd for the caller.

Signed-off-by: Dongli Zhang <[email protected]>
---
 migration/memfd.c     | 67 +++++++++++++++++++++++++++++++++++++++++++
 migration/memfd.h     | 17 +++++++++++
 migration/meson.build |  1 +
 3 files changed, 85 insertions(+)
 create mode 100644 migration/memfd.c
 create mode 100644 migration/memfd.h

diff --git a/migration/memfd.c b/migration/memfd.c
new file mode 100644
index 0000000000..0b5ef0234f
--- /dev/null
+++ b/migration/memfd.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * QEMU live migration via memfd
+ *
+ * Copyright (c) 2026 Oracle and/or its affiliates.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/cutils.h"
+#include "qemu/memfd.h"
+#include "memfd.h"
+
+QIOChannel *memfd_create_outgoing(const char *name, int *dup_fdp,
+                                  Error **errp)
+{
+    QIOChannelFile *fioc;
+    QIOChannel *ioc;
+    int fd;
+
+#ifdef CONFIG_LINUX
+    fd = qemu_memfd_create(name, 0, false, 0, 0, errp);
+#else
+    fd = -1;
+    error_setg(errp, "memfd migration is only supported on Linux");
+#endif
+
+    if (fd < 0) {
+        return NULL;
+    }
+
+    if (dup_fdp) {
+        int dup_fd = dup(fd);
+
+        if (dup_fd < 0) {
+            error_setg_errno(errp, errno,
+                             "failed to duplicate memfd migration fd");
+            close(fd);
+            return NULL;
+        }
+
+        qemu_set_cloexec(dup_fd);
+        *dup_fdp = dup_fd;
+    }
+
+    fioc = qio_channel_file_new_fd(fd);
+    ioc = QIO_CHANNEL(fioc);
+    qio_channel_set_name(ioc, name);
+    return ioc;
+}
+
+QIOChannel *memfd_open_incoming(int fd, const char *name, Error **errp)
+{
+    QIOChannelFile *fioc;
+    QIOChannel *ioc;
+
+    if (lseek(fd, 0, SEEK_SET) < 0) {
+        error_setg_errno(errp, errno, "failed to rewind memfd migration fd");
+        close(fd);
+        return NULL;
+    }
+
+    fioc = qio_channel_file_new_fd(fd);
+    ioc = QIO_CHANNEL(fioc);
+    qio_channel_set_name(ioc, name);
+    return ioc;
+}
diff --git a/migration/memfd.h b/migration/memfd.h
new file mode 100644
index 0000000000..cb6afe3eeb
--- /dev/null
+++ b/migration/memfd.h
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * QEMU live migration via memfd
+ *
+ * Copyright (c) 2026 Oracle and/or its affiliates.
+ */
+
+#ifndef QEMU_MIGRATION_MEMFD_H
+#define QEMU_MIGRATION_MEMFD_H
+
+#include "io/channel-file.h"
+
+QIOChannel *memfd_create_outgoing(const char *name, int *dup_fdp,
+                                  Error **errp);
+QIOChannel *memfd_open_incoming(int fd, const char *name, Error **errp);
+
+#endif
diff --git a/migration/meson.build b/migration/meson.build
index 0a9a5d0d37..1d852b8c6d 100644
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -23,6 +23,7 @@ system_ss.add(files(
   'fd.c',
   'file.c',
   'global_state.c',
+  'memfd.c',
   'migration.c',
   'multifd.c',
   'multifd-device-state.c',
-- 
2.43.5