Merge several virtio_blk changes from projects/virtio

The notable changes of this commit are support for disk resizing
and chases updates to the spec regarding write caching.

Contains projects/virtio commits:

r245713:
    virtio_blk: Replace __FUNCTION__ with __func__
r245714:
    virtio_blk: Use more consistent mutex name
r245715:
    virtio_blk: Print device name too if failed to reinit during dump
r245716:
    virtio_blk: Remove an unuseful ASSERT
r245723:
    virtio_blk: Record the vendor and device information
r245724:
    virtio_blk: Add resize support
r245726:
    virtio_blk: More verbose ASSERT messages
r245730:
    virtio_blk: Tweak resize announcement message
r246061:
    virtio_blk: Do not always read entire config
r246062:
    virtio_blk: Use topology to set the stripe size/offset
r246307:
    virtio_blk: Correct stripe offset calculation
r246063:
    virtio_blk: Add support for write cache enable feature
r246303:
    virtio_blk: Expand a comment
r252529:
    virtio_blk: Improve write cache handling
r252681:
    virtio_blk: Remove unneeded curly braces

MFC after:	1 month

1 files changed, 26 insertions, 4 deletions

diff --git a/share/man/man4/virtio_blk.4 b/share/man/man4/virtio_blk.4
index 7be4425..d71ca7e 100644
--- a/share/man/man4/virtio_blk.4
+++ b/share/man/man4/virtio_blk.4
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 22, 2012
+.Dd July 2, 2013
 .Dt VIRTIO_BLK 4
 .Os
 .Sh NAME
@@ -53,11 +53,33 @@ Tunables can be set at the
 .Xr loader 8
 prompt before booting the kernel or stored in
 .Xr loader.conf 5 .
-.Bl -tag -width "xxxxxx"
+.Bl -tag -width indent
 .It Va hw.vtblk.no_ident
-This tunable disables retrieving the device identification string
-from the hypervisor.
+.It Va hw.vtblk. Ns Ar X Ns Va .no_ident
+.Pp
+These tunables disable retrieving the device identification string
+from the hypervisor either globally or per-device.
 The default value is 0.
+.It Va hw.vtblk.writecache_mode
+.It Va hw.vtblk. Ns Ar X Ns Va .writecache_mode
+.Pp
+These tunables determine the write cache mode globally or per-device.
+The mode can changed only if the ConfigWCE feature is negotiated.
+Set to 0 for writethrough mode, 1 for writeback mode, and -1 to leave
+it as-is.
+The default value is to leave as-is.
+.El
+.Sh SYSCTL VARIABLES
+The following variables are available as
+.Xr sysctl 8
+variables.
+.Bl -tag -width indent
+.It Va dev.vtblk. Ns Ar X Ns Va .writecache_mode
+.Pp
+The write cache mode of the device can be either writethrough (0) or
+writeback (1).
+If the ConfigWCE feature is negotiated, the write cache mode can
+be toggled between writethrough and writeback.
 .El
 .Sh SEE ALSO
 .Xr virtio 4