On 9/22/25 15:49, Steve Sistare wrote:
To preserve CPR state across exec, create a QEMUFile based on a memfd, and
keep the memfd open across exec. Save the value of the memfd in an
environment variable so post-exec QEMU can find it.
Couldn't we preserve some memory to hand off to QEMU ? Like firmwares
An environment variable is a limited method.
Thanks,
C.
That's a short term hack right ? it's not even documented. I am sure
you something else in mind.
These new functions are called in a subsequent patch.
Signed-off-by: Steve Sistare <steven.sist...@oracle.com>
---
include/migration/cpr.h | 5 +++
migration/cpr-exec.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++++
migration/meson.build | 1 +
3 files changed, 100 insertions(+)
create mode 100644 migration/cpr-exec.c
diff --git a/include/migration/cpr.h b/include/migration/cpr.h
index 2b074d7..b84389f 100644
--- a/include/migration/cpr.h
+++ b/include/migration/cpr.h
@@ -53,4 +53,9 @@ int cpr_get_fd_param(const char *name, const char *fdname,
int index,
QEMUFile *cpr_transfer_output(MigrationChannel *channel, Error **errp);
QEMUFile *cpr_transfer_input(MigrationChannel *channel, Error **errp);
+QEMUFile *cpr_exec_output(Error **errp);
+QEMUFile *cpr_exec_input(Error **errp);
+void cpr_exec_persist_state(QEMUFile *f);
+bool cpr_exec_has_state(void);
+void cpr_exec_unpersist_state(void);
#endif
diff --git a/migration/cpr-exec.c b/migration/cpr-exec.c
new file mode 100644
index 0000000..2c32e9c
--- /dev/null
+++ b/migration/cpr-exec.c
@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2021-2025 Oracle and/or its affiliates.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/cutils.h"
+#include "qemu/memfd.h"
+#include "qapi/error.h"
+#include "io/channel-file.h"
+#include "io/channel-socket.h"
+#include "migration/cpr.h"
+#include "migration/qemu-file.h"
+#include "migration/misc.h"
+#include "migration/vmstate.h"
+#include "system/runstate.h"
+
+#define CPR_EXEC_STATE_NAME "QEMU_CPR_EXEC_STATE"
+
+static QEMUFile *qemu_file_new_fd_input(int fd, const char *name)
+{
+ g_autoptr(QIOChannelFile) fioc = qio_channel_file_new_fd(fd);
+ QIOChannel *ioc = QIO_CHANNEL(fioc);
+ qio_channel_set_name(ioc, name);
+ return qemu_file_new_input(ioc);
+}
+
+static QEMUFile *qemu_file_new_fd_output(int fd, const char *name)
+{
+ g_autoptr(QIOChannelFile) fioc = qio_channel_file_new_fd(fd);
+ QIOChannel *ioc = QIO_CHANNEL(fioc);
+ qio_channel_set_name(ioc, name);
+ return qemu_file_new_output(ioc);
+}
+
+void cpr_exec_persist_state(QEMUFile *f)
+{
+ QIOChannelFile *fioc = QIO_CHANNEL_FILE(qemu_file_get_ioc(f));
+ int mfd = dup(fioc->fd);
+ char val[16];
+
+ /* Remember mfd in environment for post-exec load */
+ qemu_clear_cloexec(mfd);
+ snprintf(val, sizeof(val), "%d", mfd);
+ g_setenv(CPR_EXEC_STATE_NAME, val, 1);
+}
+
+static int cpr_exec_find_state(void)
+{
+ const char *val = g_getenv(CPR_EXEC_STATE_NAME);
+ int mfd;
+
+ assert(val);
+ g_unsetenv(CPR_EXEC_STATE_NAME);
+ assert(!qemu_strtoi(val, NULL, 10, &mfd));
+ return mfd;
+}
+
+bool cpr_exec_has_state(void)
+{
+ return g_getenv(CPR_EXEC_STATE_NAME) != NULL;
+}
+
+void cpr_exec_unpersist_state(void)
+{
+ int mfd;
+ const char *val = g_getenv(CPR_EXEC_STATE_NAME);
+
+ g_unsetenv(CPR_EXEC_STATE_NAME);
+ assert(val);
+ assert(!qemu_strtoi(val, NULL, 10, &mfd));
+ close(mfd);
+}
+
+QEMUFile *cpr_exec_output(Error **errp)
+{
+ int mfd = memfd_create(CPR_EXEC_STATE_NAME, 0);
The build should be adjusted for Linux only.
Thanks,
C.
+
+ if (mfd < 0) {
+ error_setg_errno(errp, errno, "memfd_create failed");
+ return NULL;
+ }
+
+ return qemu_file_new_fd_output(mfd, CPR_EXEC_STATE_NAME);
+}
+
+QEMUFile *cpr_exec_input(Error **errp)
+{
+ int mfd = cpr_exec_find_state();
+
+ lseek(mfd, 0, SEEK_SET);
+ return qemu_file_new_fd_input(mfd, CPR_EXEC_STATE_NAME);
+}
diff --git a/migration/meson.build b/migration/meson.build
index 0f71544..16909d5 100644
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -16,6 +16,7 @@ system_ss.add(files(
'channel-block.c',
'cpr.c',
'cpr-transfer.c',
+ 'cpr-exec.c',
'cpu-throttle.c',
'dirtyrate.c',
'exec.c',
