On Mon, Apr 29, 2024 at 08:55:29AM -0700, Steve Sistare wrote:
> Add the cpr-exec migration mode. Usage:
> qemu-system-$arch -machine memfd-alloc=on ...
> migrate_set_parameter mode cpr-exec
> migrate_set_parameter cpr-exec-args \
> <arg1> <arg2> ... -incoming <uri>
> migrate -d <uri>
>
> The migrate command stops the VM, saves state to the URI,
> directly exec's a new version of QEMU on the same host,
> replacing the original process while retaining its PID, and
> loads state from the URI. Guest RAM is preserved in place,
> albeit with new virtual addresses.
>
> Arguments for the new QEMU process are taken from the
> @cpr-exec-args parameter. The first argument should be the
> path of a new QEMU binary, or a prefix command that exec's the
> new QEMU binary.
>
> Because old QEMU terminates when new QEMU starts, one cannot
> stream data between the two, so the URI must be a type, such as
> a file, that reads all data before old QEMU exits.
>
> Memory backend objects must have the share=on attribute, and
> must be mmap'able in the new QEMU process. For example,
> memory-backend-file is acceptable, but memory-backend-ram is
> not.
>
> The VM must be started with the '-machine memfd-alloc=on'
> option. This causes implicit ram blocks (those not explicitly
> described by a memory-backend object) to be allocated by
> mmap'ing a memfd. Examples include VGA, ROM, and even guest
> RAM when it is specified without a memory-backend object.
>
> The implementation saves precreate vmstate at the end of normal
> migration in migrate_fd_cleanup, and tells the main loop to call
> cpr_exec. Incoming qemu loads preceate state early, before objects
> are created. The memfds are kept open across exec by clearing the
> close-on-exec flag, their values are saved in precreate vmstate,
> and they are mmap'd in new qemu.
>
> Note that the memfd-alloc option is not related to memory-backend-memfd.
> Later patches add support for memory-backend-memfd, and for additional
> devices, including vfio, chardev, and more.
>
> Signed-off-by: Steve Sistare <[email protected]>
> ---
> include/migration/cpr.h | 14 +++++
> include/migration/misc.h | 3 ++
> migration/cpr.c | 131
> +++++++++++++++++++++++++++++++++++++++++++++++
> migration/meson.build | 1 +
> migration/migration.c | 21 ++++++++
> migration/migration.h | 5 +-
> migration/ram.c | 1 +
> qapi/migration.json | 30 ++++++++++-
> system/physmem.c | 2 +
> system/vl.c | 4 ++
> 10 files changed, 210 insertions(+), 2 deletions(-)
> create mode 100644 include/migration/cpr.h
> create mode 100644 migration/cpr.c
>
> +
> +void cpr_exec(char **argv)
> +{
> + MigrationState *s = migrate_get_current();
> + Error *err = NULL;
> +
> + /*
> + * Clear the close-on-exec flag for all preserved fd's. We cannot do so
> + * earlier because they should not persist across miscellaneous fork and
> + * exec calls that are performed during normal operation.
> + */
> + cpr_preserve_fds();
> +
> + execvp(argv[0], argv);
> +
> + error_setg_errno(&err, errno, "execvp %s failed", argv[0]);
This is where you could give a more direct message about the sandbox.
eg
if (errno == EPERM) {
error_append_hint("sandbox is blocking ability to exec");
}
this would also benefit the case where an external sandbox is
used, rather than qemu's built-in sandbox.
> + error_report_err(err);
> + migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
> + migrate_set_error(s, err);
> + migration_precreate_unsave();
> +}
With regards,
Daniel
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