Documentation: nfs: convert pnfs-block-server to ReST

Convert pnfs-block-server.txt to ReST and move it to admin-guide.
Content remains mostly unchanged.
Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/c06903760e690c16d9df92f5e75f80381d6326d8.1578697871.git.dwlsalmeida@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/nfs/index.rst

@@ -10,3 +10,4 @@ NFS
     nfs-rdma
     nfsd-admin-interfaces
     nfs-idmapper
+    pnfs-block-server

Documentation/filesystems/nfs/pnfs-block-server.txt → Documentation/admin-guide/nfs/pnfs-block-server.rst

+===================================
 pNFS block layout server user guide
+===================================
 
 The Linux NFS server now supports the pNFS block layout extension.  In this
 case the NFS server acts as Metadata Server (MDS) for pNFS, which in addition
@@ -22,16 +24,19 @@ If the nfsd server needs to fence a non-responding client it calls
 /sbin/nfsd-recall-failed with the first argument set to the IP address of
 the client, and the second argument set to the device node without the /dev
 prefix for the file system to be fenced. Below is an example file that shows
-how to translate the device into a serial number from SCSI EVPD 0x80:
+how to translate the device into a serial number from SCSI EVPD 0x80::
 
-cat > /sbin/nfsd-recall-failed << EOF
-#!/bin/sh
+	cat > /sbin/nfsd-recall-failed << EOF
 
-CLIENT="$1"
-DEV="/dev/$2"
-EVPD=`sg_inq --page=0x80 ${DEV} | \
-	grep "Unit serial number:" | \
-	awk -F ': ' '{print $2}'`
+.. code-block:: sh
 
-echo "fencing client ${CLIENT} serial ${EVPD}" >> /var/log/pnfsd-fence.log
-EOF
+	#!/bin/sh
+
+	CLIENT="$1"
+	DEV="/dev/$2"
+	EVPD=`sg_inq --page=0x80 ${DEV} | \
+		grep "Unit serial number:" | \
+		awk -F ': ' '{print $2}'`
+
+	echo "fencing client ${CLIENT} serial ${EVPD}" >> /var/log/pnfsd-fence.log
+	EOF