Re: [Qemu-devel] [Spice-devel] [PATCH spice 1/3] QXL interface: add a function to identify monitors in the guest

[Jonathon Jongsma]

On Fri, 2019-01-11 at 11:15 +0100, Lukáš Hrázký wrote:
> On Wed, 2019-01-09 at 11:36 -0600, Jonathon Jongsma wrote:
> > On Tue, 2019-01-08 at 16:26 +0100, Lukáš Hrázký wrote:
> > > Adds a function to let QEMU provide information to identify
> > > graphics
> > > devices and their monitors in the guest. The function
> > > (spice_qxl_set_device_info) sets the device address (e.g. a PCI
> > > path)
> > > and monitor ID -> device display ID mapping of displays exposed
> > > by
> > > given
> > > QXL interface.
> > 
> > 
> > In my previous review, I asked for a slightly more explicit
> > explanation
> > of the phrase "monitor ID" in the commit log. In this case,
> > "monitor
> > ID" is an ID specific to the QXL instance starting at 0 and
> > represents
> > the displays that are associated with that particular QXL instance.
> > 
> > Perhaps it makes sense to rename this "Qxl monitor ID"?
> 
> Sorry, I might have forgotten to incorporate some comments on the old
> series :/
> 
> To reiterate, though, what do you find unclear about the "monitor
> ID"?
> I mean maybe it should be spelled "monitor_id" to make it clearer
> what
> it refers to... Not sure if "Qxl monitor ID" helps, since it is not
> strictly related to QXL, but more to the QXL interface (which is used
> for all graphic cards, which makes it more confusing)...

Well, there are so many somewhat similar phrases being used for
slightly different things here that I'm afraid that I'll get confused
in the future when I come back to look at this stuff. But as you say,
I'm not sure there's a good way to make it clearer. You can just ignore
this bit if you want

> 
> > > Signed-off-by: Lukáš Hrázký <address@hidden>
> > > ---
> > >  server/red-qxl.c         | 44
> > > ++++++++++++++++++++++++++++++++++++++
> > >  server/spice-qxl.h       | 46
> > > ++++++++++++++++++++++++++++++++++++++++
> > >  server/spice-server.syms |  5 +++++
> > >  3 files changed, 95 insertions(+)
> > > 
> > > diff --git a/server/red-qxl.c b/server/red-qxl.c
> > > index 97940611..0ea424cd 100644
> > > --- a/server/red-qxl.c
> > > +++ b/server/red-qxl.c
> > > @@ -41,6 +41,9 @@
> > >  #include "red-qxl.h"
> > >  
> > >  
> > > +#define MAX_DEVICE_ADDRESS_LEN 256
> > > +#define MAX_MONITORS_COUNT 16
> > > +
> > >  struct QXLState {
> > >      QXLWorker qxl_worker;
> > >      QXLInstance *qxl;
> > > @@ -53,6 +56,9 @@ struct QXLState {
> > >      unsigned int max_monitors;
> > >      RedsState *reds;
> > >      RedWorker *worker;
> > > +    char device_address[MAX_DEVICE_ADDRESS_LEN];
> > > +    uint32_t device_display_ids[MAX_MONITORS_COUNT];
> > > +    size_t monitors_count;  // length of ^^^
> > >  
> > >      pthread_mutex_t scanout_mutex;
> > >      SpiceMsgDisplayGlScanoutUnix scanout;
> > > @@ -846,6 +852,44 @@ void
> > > red_qxl_gl_draw_async_complete(QXLInstance
> > > *qxl)
> > >      red_qxl_async_complete(qxl, cookie);
> > >  }
> > >  
> > > +SPICE_GNUC_VISIBLE
> > > +void spice_qxl_set_device_info(QXLInstance *instance,
> > > +                               const char *device_address,
> > > +                               uint32_t device_display_id_start,
> > > +                               uint32_t device_display_id_count)
> > > +{
> > > +    g_return_if_fail(device_address != NULL);
> > 
> > Just a thought: what if qemu calls this function twice for the same
> > instance. In theory this shouldn't happen, but should we be
> > defensive
> > and handle it somehow? Print a warning? Just overwrite the previous
> > mapping? Right now it looks like we would just overwrite.
> 
> I'm pretty sure overwriting is the correct behavior here, no logging
> needed? There may be a situation where the info changes in the
> future,
> for whatever reasons. At least this part of the code should be fine
> with it (though I'm not sure atm. if e.g. the client would cope
> well).

At the moment, it seems more likely that if this function was called
twice, it would be due to a bug somewhere. Which is why I wondered
about printing a warning or something. I can't really imagine a
scenario where we'd want to change the device info after it was set.
Anyway, like I said, it's mostly a theoretical issue at this point.

Jonathon

> 
> > > +
> > > +    size_t da_len = strnlen(device_address,
> > > MAX_DEVICE_ADDRESS_LEN);
> > > +    if (da_len >= MAX_DEVICE_ADDRESS_LEN) {
> > > +        spice_error("Device address too long: %lu > %u", da_len,
> > > MAX_DEVICE_ADDRESS_LEN);
> > 
> > Technically, I think the format string for a size_t variable is
> > %zu,
> > not %lu
> 
> You're right, didn't know that. I think I have some fixing to do :)
> 
> > > +        return;
> > > +    }
> > > +
> > > +    if (device_display_id_count > MAX_MONITORS_COUNT) {
> > > +        spice_error("Device display ID count (%u) is greater
> > > than
> > > limit %u",
> > > +                    device_display_id_count,
> > > +                    MAX_MONITORS_COUNT);
> > > +        return;
> > > +    }
> > > +
> > > +    strncpy(instance->st->device_address, device_address,
> > > MAX_DEVICE_ADDRESS_LEN);
> > > +
> > > +    g_debug("QXL Instance %d setting device address \"%s\" and
> > > monitor -> device display mapping:",
> > > +            instance->id,
> > > +            device_address);
> > > +
> > > +    // store the mapping monitor_id -> device_display_id
> > > +    for (uint32_t monitor_id = 0; monitor_id <
> > > device_display_id_count; ++monitor_id) {
> > > +        uint32_t device_display_id = device_display_id_start +
> > > monitor_id;
> > > +        instance->st->device_display_ids[monitor_id] =
> > > device_display_id;
> > > +        g_debug("   monitor ID %u -> device display ID %u",
> > > +                monitor_id, device_display_id);
> > > +    }
> > > +
> > > +    instance->st->monitors_count = device_display_id_count;
> > > +}
> > > +
> > >  void red_qxl_init(RedsState *reds, QXLInstance *qxl)
> > >  {
> > >      QXLState *qxl_state;
> > > diff --git a/server/spice-qxl.h b/server/spice-qxl.h
> > > index 0c4e75fc..547d3d93 100644
> > > --- a/server/spice-qxl.h
> > > +++ b/server/spice-qxl.h
> > > @@ -115,6 +115,52 @@ void spice_qxl_gl_draw_async(QXLInstance
> > > *instance,
> > >                               uint32_t w, uint32_t h,
> > >                               uint64_t cookie);
> > >  
> > > +/* since spice 0.14.2 */
> > > +
> > > +/**
> > > + * spice_qxl_set_device_info:
> > > + * @instance the QXL instance to set the path to
> > > + * @device_address the path of the device this QXL instance
> > > belongs
> > > to
> > > + * @device_display_id_start the starting device display ID of
> > > this
> > > interface,
> > > + *                          i.e. the one monitor ID 0 maps to
> > 
> > perhaps reword this last line:
> > i.e. the device display ID of monitor ID 0
> 
> Will do.
> 
> > > + * @device_display_id_count the total number of device display
> > > IDs
> > > on this
> > > + *                          interface
> > > + *
> > > + * Sets the device information for this QXL interface, i.e. the
> > > hardware
> > > + * address (e.g. PCI) of the graphics device and the IDs of the
> > > displays of the
> > > + * graphics device that are exposed by this interface (device
> > > display IDs).
> > > + *
> > > + * The supported device address format is:
> > > + * "pci/<DOMAIN>/<SLOT>.<FUNCTION>/.../<SLOT>.<FUNCTION>"
> > > + *
> > > + * The "pci" identifies the rest of the string as a PCI address.
> > > It
> > > is the only
> > > + * supported address at the moment, other identifiers can be
> > > introduced later.
> > > + * <DOMAIN> is the PCI domain, followed by <SLOT>.<FUNCTION> of
> > > any
> > > PCI bridges
> > > + * in the chain leading to the device. The last
> > > <SLOT>.<FUNCTION> is
> > > the
> > > + * graphics device. All of <DOMAIN>, <SLOT>, <FUNCTION> are
> > > hexadecimal numbers
> > > + * with the following number of digits:
> > > + *   <DOMAIN>: 4
> > > + *   <SLOT>: 2
> > > + *   <FUNCTION>: 1
> > > + *
> > > + * The device_display_id_{start,count} denotes the sequence of
> > > device display
> > > + * IDs that map to the zero-based sequence of monitor IDs
> > > provided
> > > by monitors
> > > + * config on this interface. For example with
> > > device_display_id_start = 2 and
> > > + * device_display_id_count = 3 you get the following mapping:
> > > + * monitor_id  ->  device_display_id
> > > + *          0  ->  2
> > > + *          1  ->  3
> > > + *          2  ->  4
> > > + *
> > > + * Note this example is unsupported in practice. The only
> > > supported
> > > cases are
> > > + * either a single device display ID (count = 1) or multiple
> > > device
> > > display IDs
> > > + * in a sequence starting from 0.
> > > + */
> > 
> > Gerd previously objected to using an example of an unsupported
> > scenario. But it doesn't seem that you changed anything here. I
> > don't
> > care too much, myself.
> 
> Right, forgot about that.
> 
> Thanks,
> Lukas
> 
> > > +void spice_qxl_set_device_info(QXLInstance *instance,
> > > +                               const char *device_address,
> > > +                               uint32_t device_display_id_start,
> > > +                               uint32_t
> > > device_display_id_count);
> > > +
> > >  typedef struct QXLDevInitInfo {
> > >      uint32_t num_memslots_groups;
> > >      uint32_t num_memslots;
> > > diff --git a/server/spice-server.syms b/server/spice-server.syms
> > > index edf04a42..ac4d9b14 100644
> > > --- a/server/spice-server.syms
> > > +++ b/server/spice-server.syms
> > > @@ -173,3 +173,8 @@ SPICE_SERVER_0.13.2 {
> > >  global:
> > >      spice_server_set_video_codecs;
> > >  } SPICE_SERVER_0.13.1;
> > > +
> > > +SPICE_SERVER_0.14.2 {
> > > +global:
> > > +    spice_qxl_set_device_info;
> > > +} SPICE_SERVER_0.13.2;
> > 
> >