Re: [PATCH V8 20/39] cpr: restart mode

[Peng Liang]

On 7/6/2022 2:29 AM, Steven Sistare wrote:
> On 7/3/2022 4:15 AM, Peng Liang wrote:
>> On 6/15/2022 10:52 PM, Steve Sistare wrote:
>>> Provide the cpr-save restart mode, which preserves the guest VM across a
>>> restart of the qemu process.  After cpr-save, the caller passes qemu
>>> command-line arguments to cpr-exec, 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 cpr-load.
>>>
>>> To use the restart mode, guest RAM must be backed by a memory-backend-file
>>> with share=on.  The '-cpr-enable restart' option causes secondary guest
>>> ram blocks (those not specified on the command line) to be allocated by
>>> mmap'ing a memfd.  The memfd values are saved in special cpr state which
>>> is retrieved after exec, and are kept open across exec, after which they
>>> are retrieved 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 and memory-backend-memfd in
>>> subsequent patches.
>>>
>>> cpr-exec syntax:
>>>   { 'command': 'cpr-exec', 'data': { 'argv': [ 'str' ] } }
>>>
>>> Add the restart mode:
>>>   { 'enum': 'CprMode', 'data': [ 'reboot', 'restart' ] }
>>>
>>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>>> ---
>>>  migration/cpr.c   | 35 +++++++++++++++++++++++++++++++++++
>>>  qapi/cpr.json     | 26 +++++++++++++++++++++++++-
>>>  qemu-options.hx   |  2 +-
>>>  softmmu/physmem.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
>>>  trace-events      |  1 +
>>>  5 files changed, 107 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/migration/cpr.c b/migration/cpr.c
>>> index 1cc8738..8b3fffd 100644
>>> --- a/migration/cpr.c
>>> +++ b/migration/cpr.c
>>> @@ -22,6 +22,7 @@ static int cpr_enabled_modes;
>>>  void cpr_init(int modes)
>>>  {
>>>      cpr_enabled_modes = modes;
>>> +    cpr_state_load(&error_fatal);
>>>  }
>>>  
>>>  bool cpr_enabled(CprMode mode)
>>> @@ -153,6 +154,37 @@ err:
>>>      cpr_set_mode(CPR_MODE_NONE);
>>>  }
>>>  
>>> +static int preserve_fd(const char *name, int id, int fd, void *opaque)
>>> +{
>>> +    qemu_clear_cloexec(fd);
>>> +    return 0;
>>> +}
>>> +
>>> +static int unpreserve_fd(const char *name, int id, int fd, void *opaque)
>>> +{
>>> +    qemu_set_cloexec(fd);
>>> +    return 0;
>>> +}
>>> +
>>> +void qmp_cpr_exec(strList *args, Error **errp)
>>> +{
>>> +    if (!runstate_check(RUN_STATE_SAVE_VM)) {
>>> +        error_setg(errp, "runstate is not save-vm");
>>> +        return;
>>> +    }
>>> +    if (cpr_get_mode() != CPR_MODE_RESTART) {
>>> +        error_setg(errp, "cpr-exec requires cpr-save with restart mode");
>>> +        return;
>>> +    }
>>> +
>>> +    cpr_walk_fd(preserve_fd, 0);
>>> +    if (cpr_state_save(errp)) {
>>> +        return;
>>> +    }
>>> +
>>> +    assert(qemu_system_exec_request(args, errp) == 0);
>>> +}
>>> +
>>>  void qmp_cpr_load(const char *filename, CprMode mode, Error **errp)
>>>  {
>>>      QEMUFile *f;
>>> @@ -189,6 +221,9 @@ void qmp_cpr_load(const char *filename, CprMode mode, 
>>> Error **errp)
>>>          goto out;
>>>      }
>>>  
>>> +    /* Clear cloexec to prevent fd leaks until the next cpr-save */
>>> +    cpr_walk_fd(unpreserve_fd, 0);
>>> +
>>>      state = global_state_get_runstate();
>>>      if (state == RUN_STATE_RUNNING) {
>>>          vm_start();
>>> diff --git a/qapi/cpr.json b/qapi/cpr.json
>>> index 11c6f88..47ee4ff 100644
>>> --- a/qapi/cpr.json
>>> +++ b/qapi/cpr.json
>>> @@ -15,11 +15,12 @@
>>>  # @CprMode:
>>>  #
>>>  # @reboot: checkpoint can be cpr-load'ed after a host reboot.
>>> +# @restart: checkpoint can be cpr-load'ed after restarting qemu.
>>>  #
>>>  # Since: 7.1
>>>  ##
>>>  { 'enum': 'CprMode',
>>> -  'data': [ 'none', 'reboot' ] }
>>> +  'data': [ 'none', 'reboot', 'restart' ] }
>>>  
>>>  ##
>>>  # @cpr-save:
>>> @@ -38,6 +39,11 @@
>>>  # issue the quit command, reboot the system, start qemu using the same
>>>  # arguments plus -S, and issue the cpr-load command.
>>>  #
>>> +# If @mode is 'restart', the checkpoint remains valid after restarting
>>> +# qemu using a subsequent cpr-exec.  Guest RAM must be backed by a
>>> +# memory-backend-file with share=on.
>>> +# To resume from the checkpoint, issue the cpr-load command.
>>> +#
>>>  # @filename: name of checkpoint file
>>>  # @mode: @CprMode mode
>>>  #
>>> @@ -48,6 +54,24 @@
>>>              'mode': 'CprMode' } }
>>>  
>>>  ##
>>> +# @cpr-exec:
>>> +#
>>> +# Restart qemu by directly exec'ing @argv[0], replacing the qemu process.
>>> +# The PID remains the same.  Must be called after cpr-save restart.
>>> +#
>>> +# @argv[0] should be the path of a new qemu binary, or a prefix command 
>>> that
>>> +# in turn exec's the new qemu binary.  The arguments must match those used
>>> +# to initially start qemu, plus the -S option so new qemu starts in a 
>>> paused
>>> +# state.
>>> +#
>>> +# @argv: arguments to be passed to exec().
>>> +#
>>> +# Since: 7.1
>>> +##
>>> +{ 'command': 'cpr-exec',
>>> +  'data': { 'argv': [ 'str' ] } }
>>> +
>>> +##
>>>  # @cpr-load:
>>>  #
>>>  # Load a virtual machine from the checkpoint file @filename that was 
>>> created
>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>> index 6e51c33..1b49360 100644
>>> --- a/qemu-options.hx
>>> +++ b/qemu-options.hx
>>> @@ -4484,7 +4484,7 @@ SRST
>>>  ERST
>>>  
>>>  DEF("cpr-enable", HAS_ARG, QEMU_OPTION_cpr_enable, \
>>> -    "-cpr-enable reboot    enable the cpr mode\n",
>>> +    "-cpr-enable reboot|restart    enable the cpr mode\n",
>>>      QEMU_ARCH_ALL)
>>>  SRST
>>>  ``-cpr-enable reboot``
>>> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
>>> index 822c424..412cc80 100644
>>> --- a/softmmu/physmem.c
>>> +++ b/softmmu/physmem.c
>>> @@ -44,6 +44,7 @@
>>>  #include "qemu/qemu-print.h"
>>>  #include "qemu/log.h"
>>>  #include "qemu/memalign.h"
>>> +#include "qemu/memfd.h"
>>>  #include "exec/memory.h"
>>>  #include "exec/ioport.h"
>>>  #include "sysemu/dma.h"
>>> @@ -1962,6 +1963,40 @@ static void dirty_memory_extend(ram_addr_t 
>>> old_ram_size,
>>>      }
>>>  }
>>>  
>>> +static bool memory_region_is_backend(MemoryRegion *mr)
>>> +{
>>> +    return !!object_dynamic_cast(mr->parent_obj.parent, 
>>> TYPE_MEMORY_BACKEND);
>>> +}
>>
>> Maybe or mr->owner is more readable?
> 
> Maybe OBJECT(mr)->parent.

Yes. I meaned "OBJECT(mr)->parent or mr->owner" originally, but "OBJECT(mr)" 
was missing
(maybe I deleted it mistakely).

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