[V2,10/11] migration: cpr-exec save and load

Commit Message

Steven Sistare June 30, 2024, 7:40 p.m. UTC

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.

These new functions are called in a subsequent patch.

Signed-off-by: Steve Sistare <[e-mail]>
---
 include/migration/cpr.h |  5 +++
 migration/cpr-exec.c    | 95 +++++++++++++++++++++++++++++++++++++++++++++++++
 migration/meson.build   |  1 +
 3 files changed, 101 insertions(+)
 create mode 100644 migration/cpr-exec.c

Patch

diff --git a/include/migration/cpr.h b/include/migration/cpr.h
index 42b4019..76d6ccb 100644
--- a/include/migration/cpr.h
+++ b/include/migration/cpr.h
@@ -25,4 +25,9 @@  void cpr_resave_fd(const char *name, int id, int fd);
 int cpr_state_save(Error **errp);
 int cpr_state_load(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..5c40457
--- /dev/null
+++ b/migration/cpr-exec.c
@@ -0,0 +1,95 @@ 
+/*
+ * Copyright (c) 2021-2024 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#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 "sysemu/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);
+
+    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 87feb4c..dd1d315 100644
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -14,6 +14,7 @@  system_ss.add(files(
   'channel.c',
   'channel-block.c',
   'cpr.c',
+  'cpr-exec.c',
   'dirtyrate.c',
   'exec.c',
   'fd.c',