Provide the cprsave restart mode, which preserves the guest VM across a
restart of the qemu process. After cprsave, the caller passes qemu
command-line arguments to cprexec, which directly exec's the new qemu
binary. The arguments must include -S so new qemu starts in a paused state.
The caller resumes the guest by calling cprload.
To use the restart mode, qemu must be started with the memfd-alloc machine
option. The memfd's are saved to the environment and kept open across exec,
after which they are found from the environment and re-mmap'd. Hence guest
ram is preserved in place, albeit with new virtual addresses in the qemu
process.
The restart mode supports vfio devices in a subsequent patch.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
What's the plan to make it work with -object memory-backend-memfd -machine memory-backend? (or memory-backend-file, I guess that should work?)
There should be some extra checks before accepting cprexec() on a misconfigured VM.
---
migration/cpr.c | 21 +++++++++++++++++++++
softmmu/physmem.c | 6 +++++-
2 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/migration/cpr.c b/migration/cpr.c
index c5bad8a..fb57dec 100644
--- a/migration/cpr.c
+++ b/migration/cpr.c
@@ -29,6 +29,7 @@
#include "sysemu/xen.h"
#include "hw/vfio/vfio-common.h"
#include "hw/virtio/vhost.h"
+#include "qemu/env.h"
QEMUFile *qf_file_open(const char *path, int flags, int mode,
const char *name, Error **errp)
@@ -108,6 +109,26 @@ done:
return;
}
+static int preserve_fd(const char *name, const char *val, void *handle)
+{
+ qemu_clr_cloexec(atoi(val));
+ return 0;
+}
+
+void cprexec(strList *args, Error **errp)
+{
+ if (xen_enabled()) {
+ error_setg(errp, "xen does not support cprexec");
+ return;
+ }
+ if (!runstate_check(RUN_STATE_SAVE_VM)) {
+ error_setg(errp, "runstate is not save-vm");
+ return;
+ }
+ walkenv(FD_PREFIX, preserve_fd, 0);
I am not convinced that relying on environment variables here is the best thing to do.
+ qemu_system_exec_request(args);
+}
+
void cprload(const char *file, Error **errp)
{
QEMUFile *f;
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index b149250..8a65ef7 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -65,6 +65,7 @@
#include "qemu/pmem.h"
#include "qemu/memfd.h"
+#include "qemu/env.h"
#include "migration/vmstate.h"
#include "qemu/range.h"
@@ -1986,7 +1987,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
} else {
name = memory_region_name(new_block->mr);
if (ms->memfd_alloc) {
- int mfd = -1; /* placeholder until next patch */
+ int mfd = getenv_fd(name);
mr->align = QEMU_VMALLOC_ALIGN;
if (mfd < 0) {
mfd = qemu_memfd_create(name, maxlen + mr->align,
@@ -1994,7 +1995,9 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
if (mfd < 0) {
return;
}
+ setenv_fd(name, mfd);
}
+ qemu_clr_cloexec(mfd);
Why clear it now, and on exec again?
new_block->flags |= RAM_SHARED;
addr = file_ram_alloc(new_block, maxlen, mfd,
false, false, 0, errp);
@@ -2246,6 +2249,7 @@ void qemu_ram_free(RAMBlock *block)
}
qemu_mutex_lock_ramlist();
+ unsetenv_fd(memory_region_name(block->mr));
QLIST_REMOVE_RCU(block, next);
ram_list.mru_block = NULL;
/* Write list before version */
--
1.8.3.1