Add an extension to the character device interface that allows character

device drivers to use arbitrary VM objects to satisfy individual mmap()
requests.
- A new d_mmap_single(cdev, &foff, objsize, &object, prot) callback is
  added to cdevsw.  This function is called for each mmap() request.
  If it returns ENODEV, then the mmap() request will fall back to using
  the device's device pager object and d_mmap().  Otherwise, the method
  can return a VM object to satisfy this entire mmap() request via
  *object.  It can also modify the starting offset into this object via
  *foff.  This allows device drivers to use the file offset as a cookie
  to identify specific VM objects.
- vm_mmap_vnode() has been changed to call vm_mmap_cdev() directly when
  mapping V_CHR vnodes.  This avoids duplicating all the cdev mmap
  handling code and simplifies some of vm_mmap_vnode().
- D_VERSION has been bumped to D_VERSION_02.  Older device drivers
  using D_VERSION_01 are still supported.

MFC after:	1 month

1 files changed, 27 insertions, 2 deletions

diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
index 284f482..8a5577c 100644
--- a/sys/kern/kern_conf.c
+++ b/sys/kern/kern_conf.c
@@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/stdarg.h>
 
 #include <fs/devfs/devfs_int.h>
+#include <vm/vm.h>
 
 static MALLOC_DEFINE(M_DEVT, "cdev", "cdev storage");
 
@@ -275,6 +276,7 @@ dead_strategy(struct bio *bp)
 
 #define dead_dump	(dumper_t *)enxio
 #define dead_kqfilter	(d_kqfilter_t *)enxio
+#define dead_mmap_single (d_mmap_single_t *)enodev
 
 static struct cdevsw dead_cdevsw = {
 	.d_version =	D_VERSION,
@@ -289,7 +291,8 @@ static struct cdevsw dead_cdevsw = {
 	.d_strategy =	dead_strategy,
 	.d_name =	"dead",
 	.d_dump =	dead_dump,
-	.d_kqfilter =	dead_kqfilter
+	.d_kqfilter =	dead_kqfilter,
+	.d_mmap_single = dead_mmap_single
 };
 
 /* Default methods if driver does not specify method */
@@ -301,6 +304,7 @@ static struct cdevsw dead_cdevsw = {
 #define no_ioctl	(d_ioctl_t *)enodev
 #define no_mmap		(d_mmap_t *)enodev
 #define no_kqfilter	(d_kqfilter_t *)enodev
+#define no_mmap_single	(d_mmap_single_t *)enodev
 
 static void
 no_strategy(struct bio *bp)
@@ -480,6 +484,23 @@ giant_mmap(struct cdev *dev, vm_offset_t offset, vm_paddr_t *paddr, int nprot)
 	return (retval);
 }
 
+static int
+giant_mmap_single(struct cdev *dev, vm_ooffset_t *offset, vm_size_t size,
+    vm_object_t *object, int nprot)
+{
+	struct cdevsw *dsw;
+	int retval;
+
+	dsw = dev_refthread(dev);
+	if (dsw == NULL)
+		return (ENXIO);
+	mtx_lock(&Giant);
+	retval = dsw->d_gianttrick->d_mmap_single(dev, offset, size, object,
+	    nprot);
+	mtx_unlock(&Giant);
+	dev_relthread(dev);
+	return (retval);
+}
 
 static void
 notify(struct cdev *dev, const char *ev)
@@ -569,7 +590,8 @@ prep_cdevsw(struct cdevsw *devsw)
 		return;
 	}
 
-	if (devsw->d_version != D_VERSION_01) {
+	if (devsw->d_version != D_VERSION_01 &&
+	    devsw->d_version != D_VERSION_02) {
 		printf(
 		    "WARNING: Device driver \"%s\" has wrong version %s\n",
 		    devsw->d_name == NULL ? "???" : devsw->d_name,
@@ -585,6 +607,8 @@ prep_cdevsw(struct cdevsw *devsw)
 		devsw->d_dump = dead_dump;
 		devsw->d_kqfilter = dead_kqfilter;
 	}
+	if (devsw->d_version == D_VERSION_01)
+		devsw->d_mmap_single = NULL;
 	
 	if (devsw->d_flags & D_NEEDGIANT) {
 		if (devsw->d_gianttrick == NULL) {
@@ -613,6 +637,7 @@ prep_cdevsw(struct cdevsw *devsw)
 	FIXUP(d_mmap,		no_mmap,	giant_mmap);
 	FIXUP(d_strategy,	no_strategy,	giant_strategy);
 	FIXUP(d_kqfilter,	no_kqfilter,	giant_kqfilter);
+	FIXUP(d_mmap_single,	no_mmap_single,	giant_mmap_single);
 
 	if (devsw->d_dump == NULL)	devsw->d_dump = no_dump;