Re: [Qemu-devel] [PATCH] Migration compatibility for serial

[Michael S. Tsirkin]

On Tue, Jun 16, 2015 at 07:54:09PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> Older QEMUs dont understand the new (sub)sections that
> may be generated in the serial device.   Limit their generation
> to newer machine types.
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>

I don't see a problem with this, but the specific
interface is unfortunate: this spreads versioning
info around which we don't normally do.
Instead, please add specific flags, e.g.
        serial_has_recv_fifo

Also, is it really enough to just skip a bunch of
stuff on load? For example, I notice that before
        7385b275d9ae8bdf3c012bc4e2ae9779fcea6312
we used to generate interrupts on loadvm -
isn't that needed in this compat mode?



> ---
>  hw/char/serial.c         | 19 +++++++++++++------
>  hw/i386/pc_piix.c        |  2 ++
>  hw/i386/pc_q35.c         |  2 ++
>  hw/ppc/spapr.c           |  2 ++
>  include/hw/char/serial.h |  3 +++
>  5 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/char/serial.c b/hw/char/serial.c
> index 513d73c..ef31df3 100644
> --- a/hw/char/serial.c
> +++ b/hw/char/serial.c
> @@ -103,6 +103,9 @@ do { fprintf(stderr, "serial: " fmt , ## __VA_ARGS__); } 
> while (0)
>  do {} while (0)
>  #endif
>  
> +/* Force migration compatibility of pre-2.2 machine types */
> +bool serial_migrate_pre_2_2;
> +
>  static void serial_receive1(void *opaque, const uint8_t *buf, int size);
>  
>  static inline void recv_fifo_put(SerialState *s, uint8_t chr)
> @@ -646,6 +649,10 @@ static bool serial_thr_ipending_needed(void *opaque)
>  {
>      SerialState *s = opaque;
>  
> +    if (serial_migrate_pre_2_2) {
> +        return false;
> +    }
> +
>      if (s->ier & UART_IER_THRI) {
>          bool expected_value = ((s->iir & UART_IIR_ID) == UART_IIR_THRI);
>          return s->thr_ipending != expected_value;
> @@ -672,7 +679,7 @@ static const VMStateDescription 
> vmstate_serial_thr_ipending = {
>  static bool serial_tsr_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return s->tsr_retry != 0;
> +    return !serial_migrate_pre_2_2 && s->tsr_retry != 0;
>  }
>  
>  static const VMStateDescription vmstate_serial_tsr = {
> @@ -691,7 +698,7 @@ static const VMStateDescription vmstate_serial_tsr = {
>  static bool serial_recv_fifo_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return !fifo8_is_empty(&s->recv_fifo);
> +    return !serial_migrate_pre_2_2 && !fifo8_is_empty(&s->recv_fifo);
>  
>  }
>  
> @@ -709,7 +716,7 @@ static const VMStateDescription vmstate_serial_recv_fifo 
> = {
>  static bool serial_xmit_fifo_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return !fifo8_is_empty(&s->xmit_fifo);
> +    return !serial_migrate_pre_2_2 && !fifo8_is_empty(&s->xmit_fifo);
>  }
>  
>  static const VMStateDescription vmstate_serial_xmit_fifo = {
> @@ -726,7 +733,7 @@ static const VMStateDescription vmstate_serial_xmit_fifo 
> = {
>  static bool serial_fifo_timeout_timer_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return timer_pending(s->fifo_timeout_timer);
> +    return !serial_migrate_pre_2_2 && timer_pending(s->fifo_timeout_timer);
>  }
>  
>  static const VMStateDescription vmstate_serial_fifo_timeout_timer = {
> @@ -743,7 +750,7 @@ static const VMStateDescription 
> vmstate_serial_fifo_timeout_timer = {
>  static bool serial_timeout_ipending_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return s->timeout_ipending != 0;
> +    return !serial_migrate_pre_2_2 && s->timeout_ipending != 0;
>  }
>  
>  static const VMStateDescription vmstate_serial_timeout_ipending = {
> @@ -760,7 +767,7 @@ static const VMStateDescription 
> vmstate_serial_timeout_ipending = {
>  static bool serial_poll_needed(void *opaque)
>  {
>      SerialState *s = (SerialState *)opaque;
> -    return s->poll_msl >= 0;
> +    return !serial_migrate_pre_2_2 && s->poll_msl >= 0;
>  }
>  
>  static const VMStateDescription vmstate_serial_poll = {
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index e142f75..d6d596c 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -39,6 +39,7 @@
>  #include "hw/kvm/clock.h"
>  #include "sysemu/sysemu.h"
>  #include "hw/sysbus.h"
> +#include "hw/char/serial.h"
>  #include "hw/cpu/icc_bus.h"
>  #include "sysemu/arch_init.h"
>  #include "sysemu/block-backend.h"
> @@ -344,6 +345,7 @@ static void pc_compat_2_1(MachineState *machine)
>      x86_cpu_compat_set_features("core2duo", FEAT_1_ECX, CPUID_EXT_VMX, 0);
>      x86_cpu_compat_kvm_no_autodisable(FEAT_8000_0001_ECX, CPUID_EXT3_SVM);
>      pcms->enforce_aligned_dimm = false;
> +    serial_migrate_pre_2_2 = true;
>  }
>  
>  static void pc_compat_2_0(MachineState *machine)
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index b68263d..a211f21 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -32,6 +32,7 @@
>  #include "sysemu/arch_init.h"
>  #include "hw/i2c/smbus.h"
>  #include "hw/boards.h"
> +#include "hw/char/serial.h"
>  #include "hw/timer/mc146818rtc.h"
>  #include "hw/xen/xen.h"
>  #include "sysemu/kvm.h"
> @@ -328,6 +329,7 @@ static void pc_compat_2_1(MachineState *machine)
>      x86_cpu_compat_set_features("coreduo", FEAT_1_ECX, CPUID_EXT_VMX, 0);
>      x86_cpu_compat_set_features("core2duo", FEAT_1_ECX, CPUID_EXT_VMX, 0);
>      x86_cpu_compat_kvm_no_autodisable(FEAT_8000_0001_ECX, CPUID_EXT3_SVM);
> +    serial_migrate_pre_2_2 = true;
>  }
>  
>  static void pc_compat_2_0(MachineState *machine)
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 01f8da8..f2673da 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -39,6 +39,7 @@
>  #include "qom/cpu.h"
>  
>  #include "hw/boards.h"
> +#include "hw/char/serial.h"
>  #include "hw/ppc/ppc.h"
>  #include "hw/loader.h"
>  
> @@ -1863,6 +1864,7 @@ static void spapr_compat_2_2(Object *obj)
>  static void spapr_compat_2_1(Object *obj)
>  {
>      spapr_compat_2_2(obj);
> +    serial_migrate_pre_2_2 = true;
>  }
>  
>  static void spapr_machine_2_3_instance_init(Object *obj)
> diff --git a/include/hw/char/serial.h b/include/hw/char/serial.h
> index 15beb6b..527d728 100644
> --- a/include/hw/char/serial.h
> +++ b/include/hw/char/serial.h
> @@ -94,4 +94,7 @@ SerialState *serial_mm_init(MemoryRegion *address_space,
>  #define TYPE_ISA_SERIAL "isa-serial"
>  void serial_hds_isa_init(ISABus *bus, int n);
>  
> +/* Force migration compatibility of pre-2.2 machine types */
> +extern bool serial_migrate_pre_2_2;
> +
>  #endif
> -- 
> 2.4.3