Clarifications of a number of points in xen.4, and some additional device

driver information from gibbs@.

MFC after:	3 days

1 files changed, 17 insertions, 12 deletions

diff --git a/share/man/man4/xen.4 b/share/man/man4/xen.4
index 57adc8a..6470635 100644
--- a/share/man/man4/xen.4
+++ b/share/man/man4/xen.4
@@ -86,17 +86,18 @@ the amd64 architecture, and require
 Para-virtualized device drivers are required in order to support certain
 functionality, such as processing management requests, returning idle
 physical memory pages to the hypevisor, etc.
-.Ss Para-virtualized drivers
+.Ss Xen DomU device drivers
 Adding
 .Cd "options xenpci"
-to the kernel configuration enables the Xen para-virtualized drivers:
+to the kernel configuration enables the Xen administrative or
+para-virtualized drivers:
 .Bl -hang -offset indent -width blkfront
 .It Nm balloon
 Allow physical memory pages to be returned to the hypervisor as a result of
 manual tuning or automatic policy.
 .It Nm blkback
-Exports local block devices to other Xen domains where they can then be
-imported via
+Exports local block devices or files to other Xen domains where they can
+then be imported via
 .Nm blkfront .
 .It Nm blkfront
 Import block devices from other Xen domains as local block devices, to be
@@ -118,13 +119,16 @@ imported via
 Import network interfaces from other Xen domains as local network interfaces,
 which may be used for IPv4, IPv6, etc.
 .It Nm pcifront
-No description.
+Allow physical PCI devices to be passed through into a PV domain.
 .It Nm xenpci
-No description.
+Represents the Xen PCI device, an emulated PCI device that is exposed to
+HVM domains.
+This device allows detection of the Xen hypervisor, and provides interrupt
+and shared memory services required to interact with the hypervisor.
 .El
-.Ss Performance
+.Ss Performance considerations
 In general, PV drivers will perform better than emulated hardware, and are
-the recommended configuration.
+the recommended configuration for HVM installations.
 .Pp
 Using a hypervisor introduces a second layer of scheduling that may limit the
 effectiveness of certain
@@ -168,7 +172,8 @@ amd64.
 .Pp
 Para-virtualized drivers under hardware-assisted virtualization (HVM) kernel
 are only supported on amd64, not i386.
-.P
-As of this release, Xen DomU support is not heavily tested; instability has
-been reported during VM migration of PV kernels, and certain PV driver
-features, such as the balloon driver, are under-exercised.
+.Pp
+As of this release, Xen PV DomU support is not heavily tested; instability
+has been reported during VM migration of PV kernels.
+.Pp
+Certain PV driver features, such as the balloon driver, are under-exercised.