MP Synchronization Levels on a Uniprocessor

This section describes how modules and drivers can use MP synchronization levels on a uniprocessor system to protect their private data structures against interrupts. Please read "Writing MP Scalable Modules and Drivers" in this chapter and "STREAMS/UX Uniprocessor Synchronization" in Chapter 3 before reading this section.

In addition to the techniques described under "Driver and Module Synchronization" in Chapter 3, modules and drivers can use MP synchronization levels to protect their private structures against interrupts. By default STREAMS/UX configures modules and drivers to use queue pair synchronization. This is why modules and drivers do not need to raise the spl level to protect their data if software running on the ICS sends a message to a stream. Suppose an interrupt occurs while one of a queue pair's entry points is running. STREAMS/UX will re-schedule sending the message to the stream to after the entry point finishes executing. You can configure uniprocessor modules and drivers to use synchronization levels other than queue pair synchronization if they need more protection.

For example, you could configure a module to use module synchronization if multiple instances of the module share the same data structure, and if the module updates the structure when it is running on the ICS. If you configure the module to use module synchronization, STREAMS/UX will wait until no instances of the module are running before sending it a message. Alternatively, you could change the module to raise the spl level while accessing the shared structure.

You configure synchronization levels for modules and drivers that run on a uniprocessor system in the same way as for MP scalable modules and drivers. You must specify the synchronization level the module or driver uses, and if the module or driver requires elsewhere synchronization, you must specify a sync name. The sync name indicates which modules and drivers belong to a group. Pick a sync name with 8 or fewer characters, and configure the name for each member of the group. You configure the synchronization level and the sync name in either the master file $STREAMS_DVR_SYNC table or in an install function streams_info_t structure.

You can configure modules and drivers to use a particular synchronization level whether or not they are MP scalable, run under UP emulation, or only run on a uniprocessor system. The section "Configuring MP Scalable Modules and Drivers" in this chapter shows examples of configuring MP scalable modules and drivers to use synchronization levels. There is no difference between configuring modules and drivers which run only on a uniprocessor system and modules and drivers which run under UP emulation. Examples of configuring uniprocesor/UP emulation modules and drivers are shown below. Examples are given for both master file entries and module and driver install functions. See Chapter 5 for more information about configuring modules and drivers.

MASTER FILE $DEVICE TABLE CONFIGURATION
 
* name   handle type mask  block char
*
$DEVICE
A        Ainfo   40  2000   -1   -1   /* UP module, since 0x10000 not in mask */
B        Binfo   40  2000   -1   -1   /* UP module, since 0x10000 not in mask */
C        Cinfo   40  2000   -1   -1   /* UP module, since 0x10000 not in mask */
D        Dinfo   21  20FC   -1   116  /* UP driver, since 0x10000 not in mask */
 
$$$
* name   sync level         sync name
*
$STREAMS_DVR_SYNC
A        sync_module                  /* Module uses synch level */
B        sync_module                  /* Module uses synch level */
C        sync_elsewhere     netsync   /* Module uses synch level & name */
D        sync_elsewhere     netsync   /* Driver uses synch level & name */
$$$

INSTALL FUNCTION CONFIGURATION
 
B MODULE
 
static streams_info_t b_str_info = {  /* streams information */
    "B",                              /* name */
    -1,                               /* major number */
    { &brinit, &bwinit, NULL, NULL },  /* streamtab */
    STR_IS_MODULE | STR_SYSV4_OPEN,    /*NOTE* MGR_IS_MP not specified */

    SQLVL_MODULE,                     /*NOTE* synch level specified */
     "",                              /* sync name */
}
 
int
B_install()
{
   int retval;
 
   return(str_install(&b_str_info));
 
}
 
D DRIVER
 
static drv_info_t d_drv_info = {   /* driver information */
     "D",                          /* name */
     "pseudo",                     /* class */
     DRV_CHAR | DRV_PSEUDO,        /*NOTE* DRV_MP_SAFE flag not specified */

     -1,                           /* block major number */
     -1                        /* dynamically assigned character major number */

    NULL, NULL, NULL,       /* cdio, gio_private,and cdio_private structures 
*/         
                                          structures */
}

static drv_ops_t d_drv_ops = {      /* driver entry points */
      NULL,                         /* open */
      NULL,                         /* close */
      NULL,                         /* strategy */
      NULL,                         /* dump */
      NULL,                         /* psize */
      NULL,                         /* mount */
      NULL,                         /* read */
      NULL,                         /* write */
      NULL,                         /* ioctl */
      NULL,                         /* select */
      NULL,                         /* option1 */
      NULL, NULL, NULL, NULL,       /* reserved entry points */
      0,                            /* device flags */
}

static streams_info_t d_str_info =  {  /* streams information */
      "D",                            /* name */
        -1,                           /* dynamically assigned major number */
      { &drinit, &dwinit, NULL, NULL}, /* streamtab */
      STR_IS_DEVICE | STR_SYSV4_OPEN, /*NOTE* MGR_IS_MP flag not specified */
      SQLVL_ELSEWHERE,                /*NOTE* synch level specified*/
      "netsync",                      /*NOTE* sync name specified */
}
 
int
D_install()
{
    int retval;
 
    /* Configure driver and obtain dynamically assigned major number. */
    if ((retval = install_driver(&d_drv_info, &d_drv_ops)) != 0)
       return(retval);
 
    /* Configure streams specific parameters. */
    if ((retval = str_install(&d_str_info)) != 0) {
       uninstall_driver(&d_drv_info);
       return(retval);
    }
 
    /* Success */
    return 0;
 
}

static streams_info_t d_str_info =  {  /* streams information */
      "D",                            /* name */
        -1,                           /* dynamically assigned major number */
      { &drinit, &dwinit, NULL, NULL}, /* streamtab */
      STR_IS_DEVICE | STR_SYSV4_OPEN, /*NOTE* MGR_IS_MP flag not specified */
      SQLVL_ELSEWHERE,                /*NOTE* synch level specified*/
      "netsync",                      /*NOTE* sync name specified */
}
 
int
D_install()
{
    int retval;
 
    /* Configure driver and obtain dynamically assigned major number. */
    if ((retval = install_driver(&d_drv_info, &d_drv_ops)) != 0)
       return(retval);
 
    /* Configure streams specific parameters. */
    if ((retval = str_install(&d_str_info)) != 0) {
       uninstall_driver(&d_drv_info);
       return(retval);
    }
 
    /* Success */
    return 0;
 
}

The following table indicates if spinlocks can be held across calls to different STREAMS/UX utilities. Also, it specifies if the SVR4 MP STREAMS/UX utilities have the same restrictions.

Table 4-1 Holding Module or Driver Defined Spinlocks While Calling Utilities

Utility	Spinlocks Can Be Held Across Call?	Differs From SVR4 MP?
`adjmsg`	Yes	No
`allocb`	Yes, if use STREAMS/UX user lock orders.	No
`backq`	Yes	No
`bcanput`	Yes, if use STREAMS/UX user lock orders.	No
`bcanputnext`	Yes, if use STREAMS/UX user lock orders.	No
`bcopy`	Yes	No
`bufcall`	Yes, if use STREAMS/UX user lock orders.
`bzero`	Yes	No
`canput`	Yes, if use STREAMS/UX user lock orders.	No
`canputnext`	Yes, if use STREAMS/UX user lock orders.	No
`cmn_err`	No	Yes
`copyb`	Yes, if use STREAMS/UX user lock orders.	No
`copymsg`	Yes, if use STREAMS/UX user lock orders.	No
`datamsg`	Yes	No
`delay`	No	No
`drv_getparm`	Yes	No
`drv_priv`	Yes	No
`dupb`	Yes, if use STREAMS/UX user lock orders.	No
`dupmsg`	Yes, if use STREAMS/UX user lock orders.	No
`enableok`	Yes, if use STREAMS/UX user lock orders.	No
`esballoc`	Yes, if use STREAMS/UX user lock orders.	No
`esbbcall`	Yes, if use STREAMS/UX user lock orders.	No
`flushband`	Yes, if use STREAMS/UX user lock orders (flushband may call user `esballoc` free routines).	No
`flushq`	Yes, if use STREAMS/UX user lock orders (flushq may call user `esballoc` free routines).	No
`freeb`	Yes, if use STREAMS/UX user lock orders (freeb may call user `esballoc` free routines).	No
`freemsg`	Yes, if use STREAMS/UX user lock orders (`freemsg` may call user `esballoc` free routines).	No
`freezestr`	Yes	No
`getadmin`	Yes, if use STREAMS/UX user lock orders.	No
`getmid`	Yes, if use STREAMS/UX user lock orders.	No
`getmajor`	Yes	No
`getminor`	Yes	No
`getq`	Yes, if use STREAMS/UX user lock orders.	No
`insq`	Yes, if use STREAMS/UX user lock orders.	No
`itimeout`	Yes, if use STREAMS/UX user lock orders.	No
`kmem_alloc`	Yes, if use STREAMS/UX user lock orders and KM_NOSLEEP.	No
`kmem_free`	Yes, if use STREAMS/UX user lock orders.	No
`linkb`	Yes	No
`LOCK`	Yes, if use lock orders correctly.	No
`LOCK_ALLOC`	No	Yes
`LOCK_DEALLOC`	Yes, if use STREAMS/UX user lock orders.	No
`major`	Yes	No
`makedev`	Yes	No
`makedevice`	Yes	No
`max`	Yes	No
`min`	Yes	No
`minor`	Yes	No
`msgdsize`	Yes	No
`msgpullup`	Yes, if use STREAMS/UX user lock orders.	No
`noenable`	Yes, if use STREAMS/UX user lock orders.	No
`OTHERQ`	Yes	No
`pcmsg`	Yes	No
`pullupmsg`	Yes, if use STREAMS/UX user lock orders.	No
`put`	No	No
`putbq`	Yes, if use STREAMS/UX user lock orders.	No
`putctl`	No	No
`putctl1`	No	No
`putctl2`	No	No
`putnext`	No	No
`putnextctl`	No	No
`putnextctl1`	No	No
`putnextctl2`	No	No
`putq`	Yes, if use STREAMS/UX user lock orders, and does not pass driver's read queue or lower mux's write queue.	Yes
`qenable`	Yes, if use STREAMS/UX user lock orders.	No
`qprocsoff`	Yes	Yes
`qprocson`	Yes	Yes
`qreply`	No	No
`qsize`	Yes	No
`RD`	Yes, if use STREAMS/UX user lock orders.	No
`rmvb`	Yes	No
`rmvq`	Yes, if use STREAMS/UX user lock orders.	No
`SAMESTR`	Yes, if use STREAMS/UX user lock orders.	No
`sleep`	No	No
`spln`	No	Yes
`splstr`	No	Yes
`streams_put`	No	No
`streams_get_sleep_lock`	Yes, if use STREAMS/UX user lock orders.	No
`strlog`	No	Yes
`strqget`	Yes, if use STREAMS/UX user lock orders.	No
`strqset`	Yes, if use STREAMS/UX user lock orders.	No
`SV_ALLOC`	Yes, if use STREAMS/UX user lock orders and KM_NOSLEEP.	No
`SV_BROADCAST`	Yes, if use STREAMS/UX user lock orders.	No
`SV_DEALLOC`	Yes, if use STREAMS/UX user lock orders.	No
`SV_WAIT`	No, except for `lkp` parameter lock.	No
`SV_WAIT_SIG`	No, except for `lkp` parameter lock.	No
`testb`	Yes, if use STREAMS/UX user lock orders.	No
`timeout`	Yes, if use STREAMS/UX user lock orders.	No
`TRYLOCK`	Yes	No
`unbufcall`	No	No
`unfreezestr`	Yes	No
`unlinkb`	Yes	No
`UNLOCK`	Yes	No
`untimeout`	Yes, if locks can be held across call to timeout callback function.	No
`unweldq`	Yes, if use STREAMS/UX user lock orders.	No
`vtop`	Yes	No
`wakeup`	Yes, if use STREAMS/UX user lock orders.	No
`weldq`	Yes, if use STREAMS/UX user lock orders.	No
`WR`	Yes, if use STREAMS/UX user lock orders.	No

MP Synchronization Levels on a Uniprocessor

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