This RFC adds a virtual device for snapshot/restores within QEMU. I am working
on this as a part of QEMU Google Summer of Code 2022. Fast snapshot/restores
within QEMU is helpful for code fuzzing.
I reused the migration code for saving and restoring virtual device and CPU
state. As for the RAM, I am using a simple COW mmaped file to do restores.
The loadvm migration function I used for doing restores only worked after I
called it from a qemu_bh. I'm not sure if I should run the migration code in a
separate thread (see patch 3), since currently it is running as a part of the
device code in the vCPU thread.
This is a rough first revision and feedback on the cpu and device state restores
is appreciated.
To test locally, boot up any linux distro. I used the following C file to
interact with the PCI snapshot device:
#include <stdio.h>
#include <stdint.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
int main() {
int fd = open("/sys/bus/pci/devices/0000:00:04.0/resource0", O_RDWR |
O_SYNC);
size_t size = 1024 * 1024;
uint32_t* memory = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, 0);
printf("%x\n", memory[0]);
int a = 0;
memory[0] = 0x101; // save snapshot
printf("before: value of a = %d\n", a);
a = 1;
printf("middle: value of a = %d\n", a);
memory[0] = 0x102; // load snapshot
printf("after: value of a = %d\n", a);
return 0;
}
Richard Liu (3):
create skeleton snapshot device and add docs
implement ram save/restore
use migration code for cpu and device save/restore
docs/devel/snapshot.rst | 26 +++++++
hw/i386/Kconfig | 1 +
hw/misc/Kconfig | 3 +
hw/misc/meson.build | 1 +
hw/misc/snapshot.c | 164 ++++++++++++++++++++++++++++++++++++++++
migration/savevm.c | 84 ++++++++++++++++++++
migration/savevm.h | 3 +
7 files changed, 282 insertions(+)
create mode 100644 docs/devel/snapshot.rst
create mode 100644 hw/misc/snapshot.c
--
2.35.1
