filesystems.5: Add cross references for ext filesystems

Signed-off-by: Stéphane Aulery <saulery@free.fr>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man5/filesystems.5

@@ -77,6 +77,7 @@ extended filesystem
 .B ext2
 offers the best performance (in terms of speed and CPU usage) of
 the filesystems supported under Linux.
+.RB See " ext2 " (5).
 .TP
 .B ext3
 is a journaling version of the
@@ -85,6 +86,7 @@ filesystem.
 It is easy to
 switch back and forth between
 .BR ext2 " and " ext3 .
+.RB See " ext3 " (5).
 .TP
 .B ext4
 is a set of upgrades to
@@ -92,6 +94,7 @@ is a set of upgrades to
 including substantial performance and
 reliability enhancements,
 plus large increases in volume, file, and directory size limits.
+.RB See " ext4 " (5).
 .TP
 .B Reiserfs
 is a journaling filesystem, designed by Hans Reiser,
@@ -202,6 +205,9 @@ you need special programs, which can be found at
 .UR ftp://linux01.gwdg.de\:/pub\:/ncpfs
 .UE .
 .SH SEE ALSO
+.BR ext2 (5),
+.BR ext3 (5),
+.BR ext4 (5),
 .BR proc (5),
 .BR fsck (8),
 .BR mkfs (8),