Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Pierre Morel 

On 19/09/2017 11:53, Cornelia Huck wrote:

On Tue, 19 Sep 2017 11:11:27 +0200
Pierre Morel  wrote:


On 13/09/2017 13:50, Halil Pasic wrote:

This is a preparation for introducing handling for indirect data
addressing and modified indirect data addressing (CCW). Here we introduce
an interface which should make the addressing scheme transparent for the
client code. Here we implement only the basic scheme (no IDA or MIDA).

Signed-off-by: Halil Pasic 
---
   hw/s390x/css.c | 55 +
   include/hw/s390x/css.h | 67 
++
   2 files changed, 122 insertions(+)



diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 0653d3c9be..79acaf99b7 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -75,6 +75,29 @@ typedef struct CMBE {
   uint32_t reserved[7];
   } QEMU_PACKED CMBE;

+typedef enum CcwDataStreamOp {
+CDS_OP_R = 0,
+CDS_OP_W = 1,
+CDS_OP_A = 2
+} CcwDataStreamOp;
+
+/** normal usage is via SuchchDev.cds instead of instantiating */
+typedef struct CcwDataStream {
+#define CDS_F_IDA   0x01
+#define CDS_F_MIDA  0x02
+#define CDS_F_I2K   0x04
+#define CDS_F_C64   0x08
+#define CDS_F_STREAM_BROKEN  0x80
+uint8_t flags;
+uint8_t at_idaw;
+uint16_t at_byte;
+uint16_t count;
+uint32_t cda_orig;
+int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op);


I would have prefer one handler per operation instead of a operation
parameter.

Is it possible to change the name of the "buf" argument to "arg".
I just think of the foollowing:
If one day we do not want to gather all IDAs into a single buffer but
keep them split, we can have something like an array of buffers as argument.


It should be possible to change the internal format should we decide to
want to do something different, so I'll leave that as-is for now.






+hwaddr cda;
+} CcwDataStream;
+



otherwise, LGTM


Is that an ack? :)




Reviewed-by: Pierre Morel


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Halil Pasic 


On 09/19/2017 01:41 PM, Pierre Morel wrote:
> On 19/09/2017 11:53, Cornelia Huck wrote:
>> On Tue, 19 Sep 2017 11:11:27 +0200
>> Pierre Morel  wrote:
>>
>>> On 13/09/2017 13:50, Halil Pasic wrote:
 This is a preparation for introducing handling for indirect data
 addressing and modified indirect data addressing (CCW). Here we introduce
 an interface which should make the addressing scheme transparent for the
 client code. Here we implement only the basic scheme (no IDA or MIDA).

 Signed-off-by: Halil Pasic 
 ---
    hw/s390x/css.c | 55 +
    include/hw/s390x/css.h | 67 
 ++
    2 files changed, 122 insertions(+)
>>
 diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
 index 0653d3c9be..79acaf99b7 100644
 --- a/include/hw/s390x/css.h
 +++ b/include/hw/s390x/css.h
 @@ -75,6 +75,29 @@ typedef struct CMBE {
    uint32_t reserved[7];
    } QEMU_PACKED CMBE;

 +typedef enum CcwDataStreamOp {
 +    CDS_OP_R = 0,
 +    CDS_OP_W = 1,
 +    CDS_OP_A = 2
 +} CcwDataStreamOp;
 +
 +/** normal usage is via SuchchDev.cds instead of instantiating */
 +typedef struct CcwDataStream {
 +#define CDS_F_IDA   0x01
 +#define CDS_F_MIDA  0x02
 +#define CDS_F_I2K   0x04
 +#define CDS_F_C64   0x08
 +#define CDS_F_STREAM_BROKEN  0x80
 +    uint8_t flags;
 +    uint8_t at_idaw;
 +    uint16_t at_byte;
 +    uint16_t count;
 +    uint32_t cda_orig;
 +    int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
 +  CcwDataStreamOp op);
>>>
>>> I would have prefer one handler per operation instead of a operation
>>> parameter.
>>>
>>> Is it possible to change the name of the "buf" argument to "arg".
>>> I just think of the foollowing:
>>> If one day we do not want to gather all IDAs into a single buffer but
>>> keep them split, we can have something like an array of buffers as argument.
>>

I had a similar idea: basically indirect data access is kind of a scatter-
gather mechanism. If one just has to mediate the data (e.g. between some
backed taking sg or some facility provided by the kernel) creating a copy
of the data (what CcwDataStream currently does) is not necessarily optimal.

I've realized that while looking at the 3270 code.

So some kind of a turn a CcwDataStream into a scatter-gather list may
come along the road. But I would like to have an use-case for that first.

>> It should be possible to change the internal format should we decide to
>> want to do something different, so I'll leave that as-is for now.
>>

Fully agree! This is internal stuff we have under full control. We can
decide any time to do something completely different looking (if we are
willing to change all the client code). So I think taking out the crystal orb
(pun intended) ain't necessary (or very productive).

>>>
>>>
>>>
 +    hwaddr cda;
 +} CcwDataStream;
 +
>>
>>> otherwise, LGTM
>>
>> Is that an ack? :)
>>
> 
> Sorry, yes it is.
> I play a little with the code before giving a RB
> Should be end of the day.
> 
>

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Pierre Morel 

On 19/09/2017 11:53, Cornelia Huck wrote:

On Tue, 19 Sep 2017 11:11:27 +0200
Pierre Morel  wrote:


On 13/09/2017 13:50, Halil Pasic wrote:

This is a preparation for introducing handling for indirect data
addressing and modified indirect data addressing (CCW). Here we introduce
an interface which should make the addressing scheme transparent for the
client code. Here we implement only the basic scheme (no IDA or MIDA).

Signed-off-by: Halil Pasic 
---
   hw/s390x/css.c | 55 +
   include/hw/s390x/css.h | 67 
++
   2 files changed, 122 insertions(+)



diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 0653d3c9be..79acaf99b7 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -75,6 +75,29 @@ typedef struct CMBE {
   uint32_t reserved[7];
   } QEMU_PACKED CMBE;

+typedef enum CcwDataStreamOp {
+CDS_OP_R = 0,
+CDS_OP_W = 1,
+CDS_OP_A = 2
+} CcwDataStreamOp;
+
+/** normal usage is via SuchchDev.cds instead of instantiating */
+typedef struct CcwDataStream {
+#define CDS_F_IDA   0x01
+#define CDS_F_MIDA  0x02
+#define CDS_F_I2K   0x04
+#define CDS_F_C64   0x08
+#define CDS_F_STREAM_BROKEN  0x80
+uint8_t flags;
+uint8_t at_idaw;
+uint16_t at_byte;
+uint16_t count;
+uint32_t cda_orig;
+int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op);


I would have prefer one handler per operation instead of a operation
parameter.

Is it possible to change the name of the "buf" argument to "arg".
I just think of the foollowing:
If one day we do not want to gather all IDAs into a single buffer but
keep them split, we can have something like an array of buffers as argument.


It should be possible to change the internal format should we decide to
want to do something different, so I'll leave that as-is for now.






+hwaddr cda;
+} CcwDataStream;
+



otherwise, LGTM


Is that an ack? :)



Sorry, yes it is.
I play a little with the code before giving a RB
Should be end of the day.


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Cornelia Huck 
On Tue, 19 Sep 2017 11:11:27 +0200
Pierre Morel  wrote:

> On 13/09/2017 13:50, Halil Pasic wrote:
> > This is a preparation for introducing handling for indirect data
> > addressing and modified indirect data addressing (CCW). Here we introduce
> > an interface which should make the addressing scheme transparent for the
> > client code. Here we implement only the basic scheme (no IDA or MIDA).
> > 
> > Signed-off-by: Halil Pasic 
> > ---
> >   hw/s390x/css.c | 55 +
> >   include/hw/s390x/css.h | 67 
> > ++
> >   2 files changed, 122 insertions(+)

> > diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> > index 0653d3c9be..79acaf99b7 100644
> > --- a/include/hw/s390x/css.h
> > +++ b/include/hw/s390x/css.h
> > @@ -75,6 +75,29 @@ typedef struct CMBE {
> >   uint32_t reserved[7];
> >   } QEMU_PACKED CMBE;
> > 
> > +typedef enum CcwDataStreamOp {
> > +CDS_OP_R = 0,
> > +CDS_OP_W = 1,
> > +CDS_OP_A = 2
> > +} CcwDataStreamOp;
> > +
> > +/** normal usage is via SuchchDev.cds instead of instantiating */
> > +typedef struct CcwDataStream {
> > +#define CDS_F_IDA   0x01
> > +#define CDS_F_MIDA  0x02
> > +#define CDS_F_I2K   0x04
> > +#define CDS_F_C64   0x08
> > +#define CDS_F_STREAM_BROKEN  0x80
> > +uint8_t flags;
> > +uint8_t at_idaw;
> > +uint16_t at_byte;
> > +uint16_t count;
> > +uint32_t cda_orig;
> > +int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
> > +  CcwDataStreamOp op);  
> 
> I would have prefer one handler per operation instead of a operation 
> parameter.
> 
> Is it possible to change the name of the "buf" argument to "arg".
> I just think of the foollowing:
> If one day we do not want to gather all IDAs into a single buffer but 
> keep them split, we can have something like an array of buffers as argument.

It should be possible to change the internal format should we decide to
want to do something different, so I'll leave that as-is for now.

> 
> 
> 
> > +hwaddr cda;
> > +} CcwDataStream;
> > +

> otherwise, LGTM

Is that an ack? :)

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Pierre Morel 

On 13/09/2017 13:50, Halil Pasic wrote:

This is a preparation for introducing handling for indirect data
addressing and modified indirect data addressing (CCW). Here we introduce
an interface which should make the addressing scheme transparent for the
client code. Here we implement only the basic scheme (no IDA or MIDA).

Signed-off-by: Halil Pasic 
---
  hw/s390x/css.c | 55 +
  include/hw/s390x/css.h | 67 ++
  2 files changed, 122 insertions(+)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 901dc6a0f3..e8d2016563 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -783,6 +783,61 @@ static CCW1 copy_ccw_from_guest(hwaddr addr, bool fmt1)
  }
  return ret;
  }
+/**
+ * If out of bounds marks the stream broken. If broken returns -EINVAL,
+ * otherwise the requested length (may be zero)
+ */
+static inline int cds_check_len(CcwDataStream *cds, int len)
+{
+if (cds->at_byte + len > cds->count) {
+cds->flags |= CDS_F_STREAM_BROKEN;
+}
+return cds->flags & CDS_F_STREAM_BROKEN ? -EINVAL : len;
+}
+
+static int ccw_dstream_rw_noflags(CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op)
+{
+int ret;
+
+ret = cds_check_len(cds, len);
+if (ret <= 0) {
+return ret;
+}
+if (op == CDS_OP_A) {
+goto incr;
+}
+ret = address_space_rw(_space_memory, cds->cda,
+   MEMTXATTRS_UNSPECIFIED, buff, len, op);
+if (ret != MEMTX_OK) {
+cds->flags |= CDS_F_STREAM_BROKEN;
+return -EINVAL;
+}
+incr:
+cds->at_byte += len;
+cds->cda += len;
+return 0;
+}
+
+void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb)
+{
+/*
+ * We don't support MIDA (an optional facility) yet and we
+ * catch this earlier. Just for expressing the precondition.
+ */
+g_assert(!(orb->ctrl1 & ORB_CTRL1_MASK_MIDAW));
+cds->flags = (orb->ctrl0 & ORB_CTRL0_MASK_I2K ? CDS_F_I2K : 0) |
+ (orb->ctrl0 & ORB_CTRL0_MASK_C64 ? CDS_F_C64 : 0) |
+ (ccw->flags & CCW_FLAG_IDA ? CDS_F_IDA : 0);
+cds->count = ccw->count;
+cds->cda_orig = ccw->cda;
+ccw_dstream_rewind(cds);
+if (!(cds->flags & CDS_F_IDA)) {
+cds->op_handler = ccw_dstream_rw_noflags;
+} else {
+assert(false);
+}
+}

  static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
   bool suspend_allowed)
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 0653d3c9be..79acaf99b7 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -75,6 +75,29 @@ typedef struct CMBE {
  uint32_t reserved[7];
  } QEMU_PACKED CMBE;

+typedef enum CcwDataStreamOp {
+CDS_OP_R = 0,
+CDS_OP_W = 1,
+CDS_OP_A = 2
+} CcwDataStreamOp;
+
+/** normal usage is via SuchchDev.cds instead of instantiating */
+typedef struct CcwDataStream {
+#define CDS_F_IDA   0x01
+#define CDS_F_MIDA  0x02
+#define CDS_F_I2K   0x04
+#define CDS_F_C64   0x08
+#define CDS_F_STREAM_BROKEN  0x80
+uint8_t flags;
+uint8_t at_idaw;
+uint16_t at_byte;
+uint16_t count;
+uint32_t cda_orig;
+int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op);


I would have prefer one handler per operation instead of a operation 
parameter.


Is it possible to change the name of the "buf" argument to "arg".
I just think of the foollowing:
If one day we do not want to gather all IDAs into a single buffer but 
keep them split, we can have something like an array of buffers as argument.





+hwaddr cda;
+} CcwDataStream;
+
  typedef struct SubchDev SubchDev;
  struct SubchDev {
  /* channel-subsystem related things: */
@@ -92,6 +115,7 @@ struct SubchDev {
  uint8_t ccw_no_data_cnt;
  uint16_t migrated_schid; /* used for missmatch detection */
  ORB orb;
+CcwDataStream cds;
  /* transport-provided data: */
  int (*ccw_cb) (SubchDev *, CCW1);
  void (*disable_cb)(SubchDev *);
@@ -240,4 +264,47 @@ SubchDev *css_create_sch(CssDevId bus_id, bool is_virtual, 
bool squash_mcss,
  /** Turn on css migration */
  void css_register_vmstate(void);

+
+void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb);
+
+static inline void ccw_dstream_rewind(CcwDataStream *cds)
+{
+cds->at_byte = 0;
+cds->at_idaw = 0;
+cds->cda = cds->cda_orig;
+}
+
+static inline bool ccw_dstream_good(CcwDataStream *cds)
+{
+return !(cds->flags & CDS_F_STREAM_BROKEN);
+}
+
+static inline uint16_t ccw_dstream_residual_count(CcwDataStream *cds)
+{
+return cds->count - cds->at_byte;
+}
+
+static inline uint16_t ccw_dstream_avail(CcwDataStream *cds)
+{
+return ccw_dstream_good(cds) ?  ccw_dstream_residual_count(cds) : 0;
+}
+
+static inline int ccw_dstream_advance(CcwDataStream *cds, int len)

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-19 Thread Cornelia Huck 
On Tue, 19 Sep 2017 10:21:42 +0800
Dong Jia Shi  wrote:

> * Halil Pasic  [2017-09-13 13:50:26 +0200]:
> 
> [...]
> 
> > diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> > index 0653d3c9be..79acaf99b7 100644
> > --- a/include/hw/s390x/css.h
> > +++ b/include/hw/s390x/css.h
> > @@ -75,6 +75,29 @@ typedef struct CMBE {
> >  uint32_t reserved[7];
> >  } QEMU_PACKED CMBE;
> > 
> > +typedef enum CcwDataStreamOp {
> > +CDS_OP_R = 0,
> > +CDS_OP_W = 1,
> > +CDS_OP_A = 2  
> 
> Nit:
> 
> typedef enum CcwDataStreamOp {
> CDS_OP_R, /* read */
> CDS_OP_W, /* write */
> CDS_OP_A  /* advance */
> } CcwDataStreamOp;
> 
> (I just keep translating 'A' as append in my mind...)

Adding comments makes sense. Done.

> 
> > +} CcwDataStreamOp;
> > +  
> [...]
> 
> > +static inline uint16_t ccw_dstream_avail(CcwDataStream *cds)
> > +{
> > +return ccw_dstream_good(cds) ?  ccw_dstream_residual_count(cds) : 0;  
>  ^^
> Nit.

Fixed.

> 
> > +}  
> 
> [...]
> 
> With or w/o responses the nit picks:
> Reviewed-by: Dong Jia Shi 
> 

Thanks!

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-18 Thread Dong Jia Shi 
* Halil Pasic  [2017-09-13 13:50:26 +0200]:

[...]

> diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> index 0653d3c9be..79acaf99b7 100644
> --- a/include/hw/s390x/css.h
> +++ b/include/hw/s390x/css.h
> @@ -75,6 +75,29 @@ typedef struct CMBE {
>  uint32_t reserved[7];
>  } QEMU_PACKED CMBE;
> 
> +typedef enum CcwDataStreamOp {
> +CDS_OP_R = 0,
> +CDS_OP_W = 1,
> +CDS_OP_A = 2

Nit:

typedef enum CcwDataStreamOp {
CDS_OP_R, /* read */
CDS_OP_W, /* write */
CDS_OP_A  /* advance */
} CcwDataStreamOp;

(I just keep translating 'A' as append in my mind...)

> +} CcwDataStreamOp;
> +
[...]

> +static inline uint16_t ccw_dstream_avail(CcwDataStream *cds)
> +{
> +return ccw_dstream_good(cds) ?  ccw_dstream_residual_count(cds) : 0;
 ^^
Nit.

> +}

[...]

With or w/o responses the nit picks:
Reviewed-by: Dong Jia Shi 

-- 
Dong Jia Shi

Re: [Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-14 Thread Cornelia Huck 
On Wed, 13 Sep 2017 13:50:26 +0200
Halil Pasic  wrote:

> This is a preparation for introducing handling for indirect data
> addressing and modified indirect data addressing (CCW). Here we introduce
> an interface which should make the addressing scheme transparent for the
> client code. Here we implement only the basic scheme (no IDA or MIDA).
> 
> Signed-off-by: Halil Pasic 
> ---
>  hw/s390x/css.c | 55 +
>  include/hw/s390x/css.h | 67 
> ++
>  2 files changed, 122 insertions(+)
> 

> +void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb)
> +{
> +/*
> + * We don't support MIDA (an optional facility) yet and we
> + * catch this earlier. Just for expressing the precondition.
> + */
> +g_assert(!(orb->ctrl1 & ORB_CTRL1_MASK_MIDAW));
> +cds->flags = (orb->ctrl0 & ORB_CTRL0_MASK_I2K ? CDS_F_I2K : 0) |
> + (orb->ctrl0 & ORB_CTRL0_MASK_C64 ? CDS_F_C64 : 0) |
> + (ccw->flags & CCW_FLAG_IDA ? CDS_F_IDA : 0);
> +cds->count = ccw->count;
> +cds->cda_orig = ccw->cda;
> +ccw_dstream_rewind(cds);
> +if (!(cds->flags & CDS_F_IDA)) {
> +cds->op_handler = ccw_dstream_rw_noflags;
> +} else {
> +assert(false);

g_assert_not_reached() might have been better; but as this is removed
anyway in patch 4, it does not matter.

> +}
> +}
>  
>  static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
>   bool suspend_allowed)
> diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> index 0653d3c9be..79acaf99b7 100644
> --- a/include/hw/s390x/css.h
> +++ b/include/hw/s390x/css.h
> @@ -75,6 +75,29 @@ typedef struct CMBE {
>  uint32_t reserved[7];
>  } QEMU_PACKED CMBE;
>  
> +typedef enum CcwDataStreamOp {
> +CDS_OP_R = 0,
> +CDS_OP_W = 1,
> +CDS_OP_A = 2
> +} CcwDataStreamOp;
> +
> +/** normal usage is via SuchchDev.cds instead of instantiating */

/* instead of /**? Can change while applying.

> +typedef struct CcwDataStream {
> +#define CDS_F_IDA   0x01
> +#define CDS_F_MIDA  0x02
> +#define CDS_F_I2K   0x04
> +#define CDS_F_C64   0x08
> +#define CDS_F_STREAM_BROKEN  0x80
> +uint8_t flags;
> +uint8_t at_idaw;
> +uint16_t at_byte;
> +uint16_t count;
> +uint32_t cda_orig;
> +int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
> +  CcwDataStreamOp op);
> +hwaddr cda;
> +} CcwDataStream;
> +
>  typedef struct SubchDev SubchDev;
>  struct SubchDev {
>  /* channel-subsystem related things: */

[Qemu-devel] [PATCH v2 1/4] s390x/css: introduce css data stream

2017-09-13 Thread Halil Pasic 
This is a preparation for introducing handling for indirect data
addressing and modified indirect data addressing (CCW). Here we introduce
an interface which should make the addressing scheme transparent for the
client code. Here we implement only the basic scheme (no IDA or MIDA).

Signed-off-by: Halil Pasic 
---
 hw/s390x/css.c | 55 +
 include/hw/s390x/css.h | 67 ++
 2 files changed, 122 insertions(+)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 901dc6a0f3..e8d2016563 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -783,6 +783,61 @@ static CCW1 copy_ccw_from_guest(hwaddr addr, bool fmt1)
 }
 return ret;
 }
+/**
+ * If out of bounds marks the stream broken. If broken returns -EINVAL,
+ * otherwise the requested length (may be zero)
+ */
+static inline int cds_check_len(CcwDataStream *cds, int len)
+{
+if (cds->at_byte + len > cds->count) {
+cds->flags |= CDS_F_STREAM_BROKEN;
+}
+return cds->flags & CDS_F_STREAM_BROKEN ? -EINVAL : len;
+}
+
+static int ccw_dstream_rw_noflags(CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op)
+{
+int ret;
+
+ret = cds_check_len(cds, len);
+if (ret <= 0) {
+return ret;
+}
+if (op == CDS_OP_A) {
+goto incr;
+}
+ret = address_space_rw(_space_memory, cds->cda,
+   MEMTXATTRS_UNSPECIFIED, buff, len, op);
+if (ret != MEMTX_OK) {
+cds->flags |= CDS_F_STREAM_BROKEN;
+return -EINVAL;
+}
+incr:
+cds->at_byte += len;
+cds->cda += len;
+return 0;
+}
+
+void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb)
+{
+/*
+ * We don't support MIDA (an optional facility) yet and we
+ * catch this earlier. Just for expressing the precondition.
+ */
+g_assert(!(orb->ctrl1 & ORB_CTRL1_MASK_MIDAW));
+cds->flags = (orb->ctrl0 & ORB_CTRL0_MASK_I2K ? CDS_F_I2K : 0) |
+ (orb->ctrl0 & ORB_CTRL0_MASK_C64 ? CDS_F_C64 : 0) |
+ (ccw->flags & CCW_FLAG_IDA ? CDS_F_IDA : 0);
+cds->count = ccw->count;
+cds->cda_orig = ccw->cda;
+ccw_dstream_rewind(cds);
+if (!(cds->flags & CDS_F_IDA)) {
+cds->op_handler = ccw_dstream_rw_noflags;
+} else {
+assert(false);
+}
+}
 
 static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
  bool suspend_allowed)
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index 0653d3c9be..79acaf99b7 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -75,6 +75,29 @@ typedef struct CMBE {
 uint32_t reserved[7];
 } QEMU_PACKED CMBE;
 
+typedef enum CcwDataStreamOp {
+CDS_OP_R = 0,
+CDS_OP_W = 1,
+CDS_OP_A = 2
+} CcwDataStreamOp;
+
+/** normal usage is via SuchchDev.cds instead of instantiating */
+typedef struct CcwDataStream {
+#define CDS_F_IDA   0x01
+#define CDS_F_MIDA  0x02
+#define CDS_F_I2K   0x04
+#define CDS_F_C64   0x08
+#define CDS_F_STREAM_BROKEN  0x80
+uint8_t flags;
+uint8_t at_idaw;
+uint16_t at_byte;
+uint16_t count;
+uint32_t cda_orig;
+int (*op_handler)(struct CcwDataStream *cds, void *buff, int len,
+  CcwDataStreamOp op);
+hwaddr cda;
+} CcwDataStream;
+
 typedef struct SubchDev SubchDev;
 struct SubchDev {
 /* channel-subsystem related things: */
@@ -92,6 +115,7 @@ struct SubchDev {
 uint8_t ccw_no_data_cnt;
 uint16_t migrated_schid; /* used for missmatch detection */
 ORB orb;
+CcwDataStream cds;
 /* transport-provided data: */
 int (*ccw_cb) (SubchDev *, CCW1);
 void (*disable_cb)(SubchDev *);
@@ -240,4 +264,47 @@ SubchDev *css_create_sch(CssDevId bus_id, bool is_virtual, 
bool squash_mcss,
 /** Turn on css migration */
 void css_register_vmstate(void);
 
+
+void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb);
+
+static inline void ccw_dstream_rewind(CcwDataStream *cds)
+{
+cds->at_byte = 0;
+cds->at_idaw = 0;
+cds->cda = cds->cda_orig;
+}
+
+static inline bool ccw_dstream_good(CcwDataStream *cds)
+{
+return !(cds->flags & CDS_F_STREAM_BROKEN);
+}
+
+static inline uint16_t ccw_dstream_residual_count(CcwDataStream *cds)
+{
+return cds->count - cds->at_byte;
+}
+
+static inline uint16_t ccw_dstream_avail(CcwDataStream *cds)
+{
+return ccw_dstream_good(cds) ?  ccw_dstream_residual_count(cds) : 0;
+}
+
+static inline int ccw_dstream_advance(CcwDataStream *cds, int len)
+{
+return cds->op_handler(cds, NULL, len, CDS_OP_A);
+}
+
+static inline int ccw_dstream_write_buf(CcwDataStream *cds, void *buff, int 
len)
+{
+return cds->op_handler(cds, buff, len, CDS_OP_W);
+}
+
+static inline int ccw_dstream_read_buf(CcwDataStream *cds, void *buff, int len)
+{
+return cds->op_handler(cds, buff, len, CDS_OP_R);
+}
+
+#define ccw_dstream_read(cds, v)