[src/pgoyette-localcount]: src/sys/dev First pass at updating the cgd(4) driv...

[pgoyette <pgoyette%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b4930a1e7160
branches:  pgoyette-localcount
changeset: 852823:b4930a1e7160
user:      pgoyette <pgoyette%NetBSD.org@localhost>
date:      Wed Jul 20 06:51:13 2016 +0000

description:
First pass at updating the cgd(4) driver for use with localcount(9)
ref-counts.

So far all I've done is to manage the ref-counts.  This will defer
removal of the driver from the devsw tables and/or the autoconf tree
while anyone has a reference to any of the device's critical data
(mostly, the softc or the device_t).  Note that these ref-counts will
only defer the removal;  once the references are released, the removal
will proceed.

On-going work is needed to identify potentially blocking operations,
and to deny any removals if such operations are in-flight.  We really
shouldn't be waiting (possibly indefinitely) for these operations to
complete, especially since removals could be attempted by the module(9)
subsystem while holding the kernel_config lock.

diffstat:

 sys/dev/cgd.c |  67 ++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 55 insertions(+), 12 deletions(-)

diffs (184 lines):

diff -r e78c990df2b8 -r b4930a1e7160 sys/dev/cgd.c
--- a/sys/dev/cgd.c     Wed Jul 20 04:33:53 2016 +0000
+++ b/sys/dev/cgd.c     Wed Jul 20 06:51:13 2016 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: cgd.c,v 1.108.2.3 2016/07/20 04:33:53 pgoyette Exp $ */
+/* $NetBSD: cgd.c,v 1.108.2.4 2016/07/20 06:51:13 pgoyette Exp $ */
 
 /*-
  * Copyright (c) 2002 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: cgd.c,v 1.108.2.3 2016/07/20 04:33:53 pgoyette Exp $");
+__KERNEL_RCSID(0, "$NetBSD: cgd.c,v 1.108.2.4 2016/07/20 06:51:13 pgoyette Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -176,6 +176,17 @@
 
 /* The code */
 
+static void
+cgd_release(dev_t dev)
+{
+       int unit = CGDUNIT(dev);
+       device_t self;
+
+       self = device_lookup_acquire(&cgd_cd, unit);
+       if (self != NULL)
+               device_release(self);
+}
+
 static struct cgd_softc *
 getcgd_softc(dev_t dev)
 {
@@ -247,6 +258,7 @@
 static struct cgd_softc *
 cgd_spawn(int unit)
 {
+       device_t self;
        cfdata_t cf;
 
        cf = malloc(sizeof(*cf), M_DEVBUF, M_WAITOK);
@@ -255,7 +267,17 @@
        cf->cf_unit = unit;
        cf->cf_fstate = FSTATE_STAR;
 
-       return device_private(config_attach_pseudo(cf));
+       if (config_attach_pseudo(cf) == NULL)
+               return NULL;
+
+       self = device_lookup_acquire(&cgd_cd, unit);
+       if (self == NULL)
+               return NULL;
+       else
+               /*
+                * Note that we return with a reference to the device!
+                */
+               return device_private(self);
 }
 
 static int
@@ -326,23 +348,30 @@
                bp->b_error = EINVAL;
                bp->b_resid = bp->b_bcount;
                biodone(bp);
+               cgd_release(bp->b_dev);
                return;
        }
 
        /* XXXrcd: Should we test for (cs != NULL)? */
        dk_strategy(&cs->sc_dksc, bp);
+       cgd_release(bp->b_dev);
        return;
 }
 
 static int
 cgdsize(dev_t dev)
 {
+       int retval;
        struct cgd_softc *cs = getcgd_softc(dev);
 
        DPRINTF_FOLLOW(("cgdsize(0x%"PRIx64")\n", dev));
        if (!cs)
-               return -1;
-       return dk_size(&cs->sc_dksc, dev);
+               retval = -1;
+       else
+               retval = dk_size(&cs->sc_dksc, dev);
+
+       cgd_release(dev);
+       return retval;
 }
 
 /*
@@ -451,6 +480,7 @@
 static void
 cgdiodone(struct buf *nbp)
 {
+       dev_t dev;
        struct  buf *obp = nbp->b_private;
        struct  cgd_softc *cs = getcgd_softc(obp->b_dev);
        struct  dk_softc *dksc = &cs->sc_dksc;
@@ -494,7 +524,14 @@
        if (obp->b_error != 0)
                obp->b_resid = obp->b_bcount;
 
+       /*
+        * copy the dev_t, finish the disk operation, and release the
+        * reference we're holding on to (from cgd_getsoftc() earlier)
+        */
+       dev = obp->b_dev;
        dk_done(dksc, obp);
+       cgd_release(dev);
+
        dk_start(dksc, NULL);
 }
 
@@ -817,8 +854,10 @@
        if (cgu->cgu_unit == -1)
                cgu->cgu_unit = unit;
 
-       if (cgu->cgu_unit < 0)
+       if (cgu->cgu_unit < 0) {
+               cgd_release(dev);
                return EINVAL;  /* XXX: should this be ENXIO? */
+       }
 
        cs = device_lookup_private(&cgd_cd, unit);
        if (cs == NULL || !DK_ATTACHED(dksc)) {
@@ -836,6 +875,7 @@
                cgu->cgu_mode = cs->sc_cdata.cf_mode;
                cgu->cgu_keylen = cs->sc_cdata.cf_keylen;
        }
+       cgd_release(dev);
        return 0;
 }
 
@@ -1030,7 +1070,7 @@
 MODULE(MODULE_CLASS_DRIVER, cgd, "dk_subr");
 
 #ifdef _MODULE
-CFDRIVER_DECL(cgd, DV_DISK, NULL);
+#include "ioconf.c"
 #endif
 
 static int
@@ -1051,8 +1091,8 @@
                error = config_init_component(cfdriver_ioconf_cgd,
                     cfattach_ioconf_cgd, cfdata_ioconf_cgd);
                if (error) {
-                       aprint_error("%s: unable to init component",
-                           cgd_cd.cd_name);
+                       aprint_error("%s: unable to init component"
+                           ", error %d", cgd_cd.cd_name, error);
                        break;
                }
 
@@ -1068,8 +1108,8 @@
                if (error) {
                        config_fini_component(cfdriver_ioconf_cgd,
                            cfattach_ioconf_cgd, cfdata_ioconf_cgd);
-                       aprint_error("%s: unable to attach devsw",
-                                   cgd_cd.cd_name);
+                       aprint_error("%s: unable to attach devsw"
+                                   ", error %d", cgd_cd.cd_name, error);
                }
 #endif
                break;
@@ -1090,9 +1130,12 @@
                /*
                 * If removal fails, re-attach our {b,c}devsw's
                 */
-               if (error)
+               if (error) {
+                       aprint_error("%s: failed to remove from autoconf"
+                           ", error %d", cgd_cd.cd_name, error);
                        devsw_attach("cgd", &cgd_bdevsw, &bmajor,
                            &cgd_cdevsw, &cmajor);
+               }
 #endif
                break;