[v8] Add vTPM emulator support for ppc64 platform

[PATCH v8 4/6] tpm_spapr: Support suspend and resume

Posted by Stefan Berger 6 years, 1 month ago

From: Stefan Berger <stefanb@linux.vnet.ibm.com>

Extend the tpm_spapr frontend with VM suspend and resume support.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
---
 hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
 hw/tpm/trace-events |  2 ++
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
index ab184fbb82..cf5c7851e7 100644
--- a/hw/tpm/tpm_spapr.c
+++ b/hw/tpm/tpm_spapr.c
@@ -76,6 +76,9 @@ typedef struct {
 
     unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
 
+    uint32_t numbytes; /* number of bytes in suspend_buffer */
+    unsigned char *suspend_buffer;
+
     TPMBackendCmd cmd;
 
     TPMBackend *be_driver;
@@ -240,6 +243,13 @@ static void tpm_spapr_request_completed(TPMIf *ti, int ret)
 
     /* a max. of be_buffer_size bytes can be transported */
     len = MIN(tpm_cmd_get_size(s->buffer), s->be_buffer_size);
+
+    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
+        /* defer delivery of response until .post_load */
+        s->numbytes = len;
+        return;
+    }
+
     rc = spapr_vio_dma_write(&s->vdev, be32_to_cpu(crq->data),
                              s->buffer, len);
 
@@ -288,11 +298,13 @@ static void tpm_spapr_reset(SpaprVioDevice *dev)
     SpaprTpmState *s = VIO_SPAPR_VTPM(dev);
 
     s->state = SPAPR_VTPM_STATE_NONE;
+    s->numbytes = 0;
 
     s->be_tpm_version = tpm_backend_get_tpm_version(s->be_driver);
 
     s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->be_driver),
                             TPM_SPAPR_BUFFER_MAX);
+    s->suspend_buffer = g_realloc(s->suspend_buffer, s->be_buffer_size);
 
     tpm_backend_reset(s->be_driver);
     tpm_spapr_do_startup_tpm(s, s->be_buffer_size);
@@ -309,9 +321,62 @@ static enum TPMVersion tpm_spapr_get_version(TPMIf *ti)
     return tpm_backend_get_tpm_version(s->be_driver);
 }
 
+/* persistent state handling */
+
+static int tpm_spapr_pre_save(void *opaque)
+{
+    SpaprTpmState *s = opaque;
+
+    tpm_backend_finish_sync(s->be_driver);
+
+    if (s->numbytes) {
+        memcpy(s->suspend_buffer, s->buffer, s->numbytes);
+    }
+
+    trace_tpm_spapr_pre_save(s->numbytes);
+    /*
+     * we cannot deliver the results to the VM since DMA would touch VM memory
+     */
+
+    return 0;
+}
+
+static int tpm_spapr_post_load(void *opaque, int version_id)
+{
+    SpaprTpmState *s = opaque;
+
+    if (s->numbytes) {
+        trace_tpm_spapr_post_load();
+
+        memcpy(s->buffer, s->suspend_buffer,
+               MIN(s->numbytes, s->be_buffer_size));
+        /* deliver the results to the VM via DMA */
+        tpm_spapr_request_completed(TPM_IF(s), 0);
+        s->numbytes = 0;
+    }
+
+    return 0;
+}
+
 static const VMStateDescription vmstate_spapr_vtpm = {
     .name = "tpm-spapr",
-    .unmigratable = 1,
+    .version_id = 1,
+    .minimum_version_id = 0,
+    .minimum_version_id_old = 0,
+    .pre_save = tpm_spapr_pre_save,
+    .post_load = tpm_spapr_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_SPAPR_VIO(vdev, SpaprTpmState),
+
+        VMSTATE_UINT8(state, SpaprTpmState),
+        VMSTATE_UINT32(numbytes, SpaprTpmState),
+        VMSTATE_VBUFFER_ALLOC_UINT32(suspend_buffer,
+                                     SpaprTpmState, 0, NULL,
+                                     numbytes),
+        /* remember DMA address */
+        VMSTATE_UINT32(crq.data, SpaprTpmState),
+        VMSTATE_END_OF_LIST(),
+    }
 };
 
 static Property tpm_spapr_properties[] = {
diff --git a/hw/tpm/trace-events b/hw/tpm/trace-events
index 9143a8eaa3..5592cec7de 100644
--- a/hw/tpm/trace-events
+++ b/hw/tpm/trace-events
@@ -67,3 +67,5 @@ tpm_spapr_do_crq_get_version(uint32_t version) "response: version %u"
 tpm_spapr_do_crq_prepare_to_suspend(void) "response: preparing to suspend"
 tpm_spapr_do_crq_unknown_msg_type(uint8_t type) "Unknown message type 0x%02x"
 tpm_spapr_do_crq_unknown_crq(uint8_t raw1, uint8_t raw2) "unknown CRQ 0x%02x 0x%02x ..."
+tpm_spapr_pre_save(uint32_t v) "Number of TPM response bytes to deliver after resume: %u"
+tpm_spapr_post_load(void) "Delivering TPM response after resume"
-- 
2.24.1

Re: [PATCH v8 4/6] tpm_spapr: Support suspend and resume

Posted by Marc-André Lureau 6 years ago

Hi

On Wed, Jan 8, 2020 at 8:14 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
>
> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
>
> Extend the tpm_spapr frontend with VM suspend and resume support.
>
> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> ---
>  hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
>  hw/tpm/trace-events |  2 ++
>  2 files changed, 68 insertions(+), 1 deletion(-)
>
> diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
> index ab184fbb82..cf5c7851e7 100644
> --- a/hw/tpm/tpm_spapr.c
> +++ b/hw/tpm/tpm_spapr.c
> @@ -76,6 +76,9 @@ typedef struct {
>
>      unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
>
> +    uint32_t numbytes; /* number of bytes in suspend_buffer */
> +    unsigned char *suspend_buffer;

Why do you need a copy suspend_buffer? Why not use and save buffer[] directly?

Also numbytes wouldn't be necessary, you would just need a bool flag
to say if the request_completed is pending.

> +
>      TPMBackendCmd cmd;
>
>      TPMBackend *be_driver;
> @@ -240,6 +243,13 @@ static void tpm_spapr_request_completed(TPMIf *ti, int ret)
>
>      /* a max. of be_buffer_size bytes can be transported */
>      len = MIN(tpm_cmd_get_size(s->buffer), s->be_buffer_size);
> +
> +    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
> +        /* defer delivery of response until .post_load */
> +        s->numbytes = len;
> +        return;
> +    }
> +
>      rc = spapr_vio_dma_write(&s->vdev, be32_to_cpu(crq->data),
>                               s->buffer, len);
>
> @@ -288,11 +298,13 @@ static void tpm_spapr_reset(SpaprVioDevice *dev)
>      SpaprTpmState *s = VIO_SPAPR_VTPM(dev);
>
>      s->state = SPAPR_VTPM_STATE_NONE;
> +    s->numbytes = 0;
>
>      s->be_tpm_version = tpm_backend_get_tpm_version(s->be_driver);
>
>      s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->be_driver),
>                              TPM_SPAPR_BUFFER_MAX);
> +    s->suspend_buffer = g_realloc(s->suspend_buffer, s->be_buffer_size);
>
>      tpm_backend_reset(s->be_driver);
>      tpm_spapr_do_startup_tpm(s, s->be_buffer_size);
> @@ -309,9 +321,62 @@ static enum TPMVersion tpm_spapr_get_version(TPMIf *ti)
>      return tpm_backend_get_tpm_version(s->be_driver);
>  }
>
> +/* persistent state handling */
> +
> +static int tpm_spapr_pre_save(void *opaque)
> +{
> +    SpaprTpmState *s = opaque;
> +
> +    tpm_backend_finish_sync(s->be_driver);
> +
> +    if (s->numbytes) {
> +        memcpy(s->suspend_buffer, s->buffer, s->numbytes);
> +    }
> +
> +    trace_tpm_spapr_pre_save(s->numbytes);
> +    /*
> +     * we cannot deliver the results to the VM since DMA would touch VM memory
> +     */
> +
> +    return 0;
> +}
> +
> +static int tpm_spapr_post_load(void *opaque, int version_id)
> +{
> +    SpaprTpmState *s = opaque;
> +
> +    if (s->numbytes) {
> +        trace_tpm_spapr_post_load();
> +
> +        memcpy(s->buffer, s->suspend_buffer,
> +               MIN(s->numbytes, s->be_buffer_size));
> +        /* deliver the results to the VM via DMA */
> +        tpm_spapr_request_completed(TPM_IF(s), 0);
> +        s->numbytes = 0;
> +    }
> +
> +    return 0;
> +}
> +
>  static const VMStateDescription vmstate_spapr_vtpm = {
>      .name = "tpm-spapr",
> -    .unmigratable = 1,
> +    .version_id = 1,
> +    .minimum_version_id = 0,
> +    .minimum_version_id_old = 0,


Yyou should leave all the fields to 0 (there is no version 0 so far).
Thus no need to have them set explicitly either.

> +    .pre_save = tpm_spapr_pre_save,
> +    .post_load = tpm_spapr_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_SPAPR_VIO(vdev, SpaprTpmState),
> +
> +        VMSTATE_UINT8(state, SpaprTpmState),
> +        VMSTATE_UINT32(numbytes, SpaprTpmState),
> +        VMSTATE_VBUFFER_ALLOC_UINT32(suspend_buffer,
> +                                     SpaprTpmState, 0, NULL,
> +                                     numbytes),
> +        /* remember DMA address */
> +        VMSTATE_UINT32(crq.data, SpaprTpmState),
> +        VMSTATE_END_OF_LIST(),
> +    }
>  };
>
>  static Property tpm_spapr_properties[] = {
> diff --git a/hw/tpm/trace-events b/hw/tpm/trace-events
> index 9143a8eaa3..5592cec7de 100644
> --- a/hw/tpm/trace-events
> +++ b/hw/tpm/trace-events
> @@ -67,3 +67,5 @@ tpm_spapr_do_crq_get_version(uint32_t version) "response: version %u"
>  tpm_spapr_do_crq_prepare_to_suspend(void) "response: preparing to suspend"
>  tpm_spapr_do_crq_unknown_msg_type(uint8_t type) "Unknown message type 0x%02x"
>  tpm_spapr_do_crq_unknown_crq(uint8_t raw1, uint8_t raw2) "unknown CRQ 0x%02x 0x%02x ..."
> +tpm_spapr_pre_save(uint32_t v) "Number of TPM response bytes to deliver after resume: %u"
> +tpm_spapr_post_load(void) "Delivering TPM response after resume"
> --
> 2.24.1
>
>


-- 
Marc-André Lureau

Re: [PATCH v8 4/6] tpm_spapr: Support suspend and resume

Posted by Stefan Berger 6 years ago

On 1/17/20 8:31 AM, Marc-André Lureau wrote:
> Hi
>
> On Wed, Jan 8, 2020 at 8:14 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
>> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
>>
>> Extend the tpm_spapr frontend with VM suspend and resume support.
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>>   hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
>>   hw/tpm/trace-events |  2 ++
>>   2 files changed, 68 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
>> index ab184fbb82..cf5c7851e7 100644
>> --- a/hw/tpm/tpm_spapr.c
>> +++ b/hw/tpm/tpm_spapr.c
>> @@ -76,6 +76,9 @@ typedef struct {
>>
>>       unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
>>
>> +    uint32_t numbytes; /* number of bytes in suspend_buffer */
>> +    unsigned char *suspend_buffer;
> Why do you need a copy suspend_buffer? Why not use and save buffer[] directly?


This addresses David's comment:

"Transferring the whole 4kiB buffer unconditionally when it mostly
won't have anything useful in it doesn't seem like a great idea."

https://lists.nongnu.org/archive/html/qemu-devel/2019-12/msg02601.html


>
> Also numbytes wouldn't be necessary, you would just need a bool flag
> to say if the request_completed is pending.
>
>> +
>>       TPMBackendCmd cmd;
>>
>>       TPMBackend *be_driver;
>> @@ -240,6 +243,13 @@ static void tpm_spapr_request_completed(TPMIf *ti, int ret)
>>
>>       /* a max. of be_buffer_size bytes can be transported */
>>       len = MIN(tpm_cmd_get_size(s->buffer), s->be_buffer_size);
>> +
>> +    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
>> +        /* defer delivery of response until .post_load */
>> +        s->numbytes = len;
>> +        return;
>> +    }
>> +
>>       rc = spapr_vio_dma_write(&s->vdev, be32_to_cpu(crq->data),
>>                                s->buffer, len);
>>
>> @@ -288,11 +298,13 @@ static void tpm_spapr_reset(SpaprVioDevice *dev)
>>       SpaprTpmState *s = VIO_SPAPR_VTPM(dev);
>>
>>       s->state = SPAPR_VTPM_STATE_NONE;
>> +    s->numbytes = 0;
>>
>>       s->be_tpm_version = tpm_backend_get_tpm_version(s->be_driver);
>>
>>       s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->be_driver),
>>                               TPM_SPAPR_BUFFER_MAX);
>> +    s->suspend_buffer = g_realloc(s->suspend_buffer, s->be_buffer_size);
>>
>>       tpm_backend_reset(s->be_driver);
>>       tpm_spapr_do_startup_tpm(s, s->be_buffer_size);
>> @@ -309,9 +321,62 @@ static enum TPMVersion tpm_spapr_get_version(TPMIf *ti)
>>       return tpm_backend_get_tpm_version(s->be_driver);
>>   }
>>
>> +/* persistent state handling */
>> +
>> +static int tpm_spapr_pre_save(void *opaque)
>> +{
>> +    SpaprTpmState *s = opaque;
>> +
>> +    tpm_backend_finish_sync(s->be_driver);
>> +
>> +    if (s->numbytes) {
>> +        memcpy(s->suspend_buffer, s->buffer, s->numbytes);
>> +    }
>> +
>> +    trace_tpm_spapr_pre_save(s->numbytes);
>> +    /*
>> +     * we cannot deliver the results to the VM since DMA would touch VM memory
>> +     */
>> +
>> +    return 0;
>> +}
>> +
>> +static int tpm_spapr_post_load(void *opaque, int version_id)
>> +{
>> +    SpaprTpmState *s = opaque;
>> +
>> +    if (s->numbytes) {
>> +        trace_tpm_spapr_post_load();
>> +
>> +        memcpy(s->buffer, s->suspend_buffer,
>> +               MIN(s->numbytes, s->be_buffer_size));
>> +        /* deliver the results to the VM via DMA */
>> +        tpm_spapr_request_completed(TPM_IF(s), 0);
>> +        s->numbytes = 0;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static const VMStateDescription vmstate_spapr_vtpm = {
>>       .name = "tpm-spapr",
>> -    .unmigratable = 1,
>> +    .version_id = 1,
>> +    .minimum_version_id = 0,
>> +    .minimum_version_id_old = 0,
>
> Yyou should leave all the fields to 0 (there is no version 0 so far).
> Thus no need to have them set explicitly either.


Ok, I will fix.

   Thanks.

Re: [PATCH v8 4/6] tpm_spapr: Support suspend and resume

Posted by Marc-André Lureau 6 years ago

On Fri, Jan 17, 2020 at 5:41 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
>
> On 1/17/20 8:31 AM, Marc-André Lureau wrote:
> > Hi
> >
> > On Wed, Jan 8, 2020 at 8:14 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
> >> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
> >>
> >> Extend the tpm_spapr frontend with VM suspend and resume support.
> >>
> >> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> >> ---
> >>   hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
> >>   hw/tpm/trace-events |  2 ++
> >>   2 files changed, 68 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
> >> index ab184fbb82..cf5c7851e7 100644
> >> --- a/hw/tpm/tpm_spapr.c
> >> +++ b/hw/tpm/tpm_spapr.c
> >> @@ -76,6 +76,9 @@ typedef struct {
> >>
> >>       unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
> >>
> >> +    uint32_t numbytes; /* number of bytes in suspend_buffer */
> >> +    unsigned char *suspend_buffer;
> > Why do you need a copy suspend_buffer? Why not use and save buffer[] directly?
>
>
> This addresses David's comment:
>
> "Transferring the whole 4kiB buffer unconditionally when it mostly
> won't have anything useful in it doesn't seem like a great idea."
>
> https://lists.nongnu.org/archive/html/qemu-devel/2019-12/msg02601.html

Oh ok.. (well really I don't think 4k (usually compressed) will really
matter much in multi-gigabytes streams ;)

>
>
> >
> > Also numbytes wouldn't be necessary, you would just need a bool flag
> > to say if the request_completed is pending.
> >
> >> +
> >>       TPMBackendCmd cmd;
> >>
> >>       TPMBackend *be_driver;
> >> @@ -240,6 +243,13 @@ static void tpm_spapr_request_completed(TPMIf *ti, int ret)
> >>
> >>       /* a max. of be_buffer_size bytes can be transported */
> >>       len = MIN(tpm_cmd_get_size(s->buffer), s->be_buffer_size);
> >> +
> >> +    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
> >> +        /* defer delivery of response until .post_load */
> >> +        s->numbytes = len;
> >> +        return;
> >> +    }
> >> +
> >>       rc = spapr_vio_dma_write(&s->vdev, be32_to_cpu(crq->data),
> >>                                s->buffer, len);
> >>
> >> @@ -288,11 +298,13 @@ static void tpm_spapr_reset(SpaprVioDevice *dev)
> >>       SpaprTpmState *s = VIO_SPAPR_VTPM(dev);
> >>
> >>       s->state = SPAPR_VTPM_STATE_NONE;
> >> +    s->numbytes = 0;
> >>
> >>       s->be_tpm_version = tpm_backend_get_tpm_version(s->be_driver);
> >>
> >>       s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->be_driver),
> >>                               TPM_SPAPR_BUFFER_MAX);
> >> +    s->suspend_buffer = g_realloc(s->suspend_buffer, s->be_buffer_size);
> >>
> >>       tpm_backend_reset(s->be_driver);
> >>       tpm_spapr_do_startup_tpm(s, s->be_buffer_size);
> >> @@ -309,9 +321,62 @@ static enum TPMVersion tpm_spapr_get_version(TPMIf *ti)
> >>       return tpm_backend_get_tpm_version(s->be_driver);
> >>   }
> >>
> >> +/* persistent state handling */
> >> +
> >> +static int tpm_spapr_pre_save(void *opaque)
> >> +{
> >> +    SpaprTpmState *s = opaque;
> >> +
> >> +    tpm_backend_finish_sync(s->be_driver);
> >> +
> >> +    if (s->numbytes) {
> >> +        memcpy(s->suspend_buffer, s->buffer, s->numbytes);
> >> +    }
> >> +
> >> +    trace_tpm_spapr_pre_save(s->numbytes);
> >> +    /*
> >> +     * we cannot deliver the results to the VM since DMA would touch VM memory
> >> +     */
> >> +
> >> +    return 0;
> >> +}
> >> +
> >> +static int tpm_spapr_post_load(void *opaque, int version_id)
> >> +{
> >> +    SpaprTpmState *s = opaque;
> >> +
> >> +    if (s->numbytes) {
> >> +        trace_tpm_spapr_post_load();
> >> +
> >> +        memcpy(s->buffer, s->suspend_buffer,
> >> +               MIN(s->numbytes, s->be_buffer_size));
> >> +        /* deliver the results to the VM via DMA */
> >> +        tpm_spapr_request_completed(TPM_IF(s), 0);
> >> +        s->numbytes = 0;
> >> +    }
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>   static const VMStateDescription vmstate_spapr_vtpm = {
> >>       .name = "tpm-spapr",
> >> -    .unmigratable = 1,
> >> +    .version_id = 1,
> >> +    .minimum_version_id = 0,
> >> +    .minimum_version_id_old = 0,
> >
> > Yyou should leave all the fields to 0 (there is no version 0 so far).
> > Thus no need to have them set explicitly either.
>
>
> Ok, I will fix.
>
>    Thanks.



-- 
Marc-André Lureau

Re: [PATCH v8 4/6] tpm_spapr: Support suspend and resume

Posted by David Gibson 6 years ago

On Fri, Jan 17, 2020 at 05:46:21PM +0400, Marc-André Lureau wrote:
> On Fri, Jan 17, 2020 at 5:41 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
> >
> > On 1/17/20 8:31 AM, Marc-André Lureau wrote:
> > > Hi
> > >
> > > On Wed, Jan 8, 2020 at 8:14 PM Stefan Berger <stefanb@linux.ibm.com> wrote:
> > >> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
> > >>
> > >> Extend the tpm_spapr frontend with VM suspend and resume support.
> > >>
> > >> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> > >> ---
> > >>   hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
> > >>   hw/tpm/trace-events |  2 ++
> > >>   2 files changed, 68 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
> > >> index ab184fbb82..cf5c7851e7 100644
> > >> --- a/hw/tpm/tpm_spapr.c
> > >> +++ b/hw/tpm/tpm_spapr.c
> > >> @@ -76,6 +76,9 @@ typedef struct {
> > >>
> > >>       unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
> > >>
> > >> +    uint32_t numbytes; /* number of bytes in suspend_buffer */
> > >> +    unsigned char *suspend_buffer;
> > > Why do you need a copy suspend_buffer? Why not use and save buffer[] directly?
> >
> >
> > This addresses David's comment:
> >
> > "Transferring the whole 4kiB buffer unconditionally when it mostly
> > won't have anything useful in it doesn't seem like a great idea."
> >
> > https://lists.nongnu.org/archive/html/qemu-devel/2019-12/msg02601.html
> 
> Oh ok.. (well really I don't think 4k (usually compressed) will really
> matter much in multi-gigabytes streams ;)

Probably not - though it is in the downtime portion of the stream.

But more to the point you can still make the size / whether you send
conditional on numbytes without having a whole separate buffer for it.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[PATCH v8 1/6] tpm: Move tpm_tis_show_buffer to tpm_util.c
[PATCH v8 2/6] spapr: Implement get_dt_compatible() callback
[PATCH v8 3/6] tpm_spapr: Support TPM for ppc64 using CRQ based interface
[PATCH v8 4/6] tpm_spapr: Support suspend and resume
[PATCH v8 5/6] hw/ppc/Kconfig: Enable TPM_SPAPR as part of PSERIES config
[PATCH v8 6/6] docs/specs/tpm: reST-ify TPM documentation