[Spice-devel] [RFC PATCH spice-server v5 01/22] Avoid using global variable for channel IDs

[Frediano Ziglio]

> 
> Acked-by: Jonathon Jongsma <jjongsma at redhat.com>
> 
> On Wed, 2017-08-30 at 16:28 +0100, Frediano Ziglio wrote:
> > This patch allocates VMC IDs by finding the first ID not used
> > instead of using a global variable and incrementing the value
> > for each channel created.
> > This solves some potential issues:
> > - remove the global state potentially making possible
> >   to use multiple SpiceServer on the same process;
> > - don't potentially overflow the variable. This can happen if
> >   channels are allocated/deallocated multiple times
> >   (currently not done by Qemu).
> > 
> > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > ---
> >  server/reds.c     | 32 ++++++++++++++++++++++++++++++++
> >  server/reds.h     |  1 +
> >  server/spicevmc.c | 10 ++++++++--
> >  3 files changed, 41 insertions(+), 2 deletions(-)
> > 
> > diff --git a/server/reds.c b/server/reds.c
> > index a738afc3..b6ecc6c6 100644
> > --- a/server/reds.c
> > +++ b/server/reds.c
> > @@ -408,6 +408,38 @@ RedChannel *reds_find_channel(RedsState *reds,
> > uint32_t type, uint32_t id)
> >      return NULL;
> >  }
> >  
> > +/* Search for first free channel id for a specific channel type.
> > + * Return first id free or <0 if not found. */
> > +int reds_get_free_channel_id(RedsState *reds, uint32_t type)
> > +{
> > +    RedChannel *channel;
> > +
> > +    // this mark if some IDs are used.
> > +    // The size of the array limits the possible id returned but
> > +    // usually the IDs used for a channel type are not much.
> > +    bool used_ids[256];
> > +

I just realized due to protocol implementation that this
size is actually not a restriction, we are limited to
256 IDs in any case (a uint8 is used).

> > +    unsigned n;
> > +
> > +    // mark id used for the specific channel type
> > +    memset(used_ids, 0, sizeof(used_ids));
> > +    GLIST_FOREACH(reds->channels, RedChannel, channel) {
> > +        uint32_t this_type, this_id;
> > +        g_object_get(channel, "channel-type", &this_type, "id",
> > &this_id, NULL);
> > +        if (this_type == type && this_id <
> > SPICE_N_ELEMENTS(used_ids)) {
> > +            used_ids[this_id] = true;
> > +        }
> > +    }
> > +
> > +    // find first ID not marked as used
> > +    for (n = 0; n < SPICE_N_ELEMENTS(used_ids); ++n) {
> > +        if (!used_ids[n]) {
> > +            return n;
> > +        }
> > +    }
> > +    return -1;
> > +}
> > +
> >  static void reds_mig_cleanup(RedsState *reds)
> >  {
> >      if (reds->mig_inprogress) {
> > diff --git a/server/reds.h b/server/reds.h
> > index ee5a46c0..4f5fc28c 100644
> > --- a/server/reds.h
> > +++ b/server/reds.h
> > @@ -48,6 +48,7 @@ uint32_t reds_get_mm_time(void);
> >  void reds_register_channel(RedsState *reds, RedChannel *channel);
> >  void reds_unregister_channel(RedsState *reds, RedChannel *channel);
> >  RedChannel *reds_find_channel(RedsState *reds, uint32_t type,
> > uint32_t id);
> > +int reds_get_free_channel_id(RedsState *reds, uint32_t type);
> >  SpiceMouseMode reds_get_mouse_mode(RedsState *reds); // used by
> > inputs_channel
> >  gboolean reds_config_get_agent_mouse(const RedsState *reds); // used
> > by inputs_channel
> >  int reds_has_vdagent(RedsState *reds); // used by inputs channel
> > diff --git a/server/spicevmc.c b/server/spicevmc.c
> > index 9305c9b4..08d9954b 100644
> > --- a/server/spicevmc.c
> > +++ b/server/spicevmc.c
> > @@ -272,7 +272,6 @@ red_vmc_channel_finalize(GObject *object)
> >  static RedVmcChannel *red_vmc_channel_new(RedsState *reds, uint8_t
> > channel_type)
> >  {
> >      GType gtype = G_TYPE_NONE;
> > -    static uint8_t id[SPICE_END_CHANNEL] = { 0, };
> >  
> >      switch (channel_type) {
> >          case SPICE_CHANNEL_USBREDIR:
> > @@ -288,11 +287,18 @@ static RedVmcChannel
> > *red_vmc_channel_new(RedsState *reds, uint8_t channel_type)
> >              g_error("Unsupported channel_type for
> > red_vmc_channel_new(): %u", channel_type);
> >              return NULL;
> >      }
> > +
> > +    int id = reds_get_free_channel_id(reds, channel_type);
> > +    if (id < 0) {
> > +        g_warning("Free ID not found creating new VMC channel");
> > +        return NULL;
> > +    }
> > +
> >      return g_object_new(gtype,
> >                          "spice-server", reds,
> >                          "core-interface",
> > reds_get_core_interface(reds),
> >                          "channel-type", channel_type,
> > -                        "id", id[channel_type]++,
> > +                        "id", id,
> >                          "handle-acks", FALSE,
> >                          "migration-flags",
> >                          (SPICE_MIGRATE_NEED_FLUSH |
> > SPICE_MIGRATE_NEED_DATA_TRANSFER),
> 

2 missing global variables to remove!

Frediano