Revert "Revert "Updated config and added reference""

This reverts commit 2229253e11.

doc/reference.texi

@@ -28,6 +28,7 @@
 * glibtop_proc_map::            Process Memory Maps.
 * glibtop_netload::             Network Load.
 * glibtop_ppp::                 PPP Usage.
+* glibtop_disk::                DISK Usage.
 @end menu
 
 @node glibtop_cpu, glibtop_mem, System Dependent, System Dependent
@@ -1343,7 +1344,7 @@ enum @{
 @end example
 
 @page
-@node glibtop_ppp,  , glibtop_netload, System Dependent
+@node glibtop_ppp, glibtop_disk, glibtop_netload, System Dependent
 @subsection PPP Statistics
 
 Library function @code{glibtop_get_ppp}:
@@ -1403,6 +1404,62 @@ We're currently offline.
 We're currently online.
 @end table
 
+@page
+@node glibtop_disk, , glibtop_ppp, System Dependent
+@subsection DISK Usage
+
+Library function @code{glibtop_get_disk}:
+
+@example
+@cartouche
+void glibtop_get_disk (glibtop_disk *buf);
+void glibtop_get_disk_l (glibtop *server, glibtop_disk *buf);
+@end cartouche
+@end example
+
+Declaration of @code{glibtop_disk} in @file{<glibtop/disk.h>}:
+
+@example
+@cartouche
+typedef struct _glibtop_disk     glibtop_disk;
+
+struct _glibtop_disk
+@{
+    xdisk_sectors_read [GLIBTOP_NDISK],
+    xdisk_time_read [GLIBTOP_NDISK],
+    xdisk_sectors_write [GLIBTOP_NDISK],
+    xdisk_time_write [GLIBTOP_NDISK],
+@};
+@end cartouche
+@end example
+
+All DISK reads and writes are measured by @dfn{sectors} which are normally 512 bytes each. 
+All disk time are measured in milliseconds which is 1/1000th of a second.
+
+@table @code
+@item xdisk_sectors_read
+Number of sectors read since system boot.
+
+@item xdisk_time_read
+Number of milliseconds spent reading since system boot.
+
+@item xdisk_sectors_write
+Number of sectors written since system boot.
+
+@item xdisk_time_write
+Number of milliseconds spent writing since system boot.
+
+@end table
+
+The @samp{xdisk_} are values from arrays of @code{GLIBTOP_NDISK} (defined in
+@file{<glibtop/disk.h>}) elements and contain one value for each DISK
+in the system.
+
+Please note that all of the disk values are absolute values measured in
+certain units since system boot. To get bandwidth values (bytes/s), you need to call @code{glibtop_disk}, save the
+result, wait some time and then call it again and divide the differences of
+the two values by the time spent reading or writing.
+
 @page
 @node Common Functions, Library Functions, System Dependent, Reference Manual
 @section Common Functions