Stop using O_EXCL by default when opening the device for writing.

gpt.8

Index: gpt.8
diff --git a/gpt.8 b/gpt.8
index 0e3acef2f999596b3317978bf710975bc45d8f83..8258ccd28177c04c9ac881d26040becdc6ab3243 100644
--- a/gpt.8
+++ b/gpt.8
@@ -83,6 +83,13 @@ command, but the intent
 is to use it to implement dry-run behaviour.
 .Pp
 The
+.Fl S
+option causes the
+.Nm
+utility to open the device for writing in shared mode. The
+default is to open in exclusive (O_EXCL) mode.
+.Pp
+The
 .Fl v
 option controls the verbosity level.
 The level increases with every occurrence of this option.
@@ -140,6 +147,7 @@ as aliases for the most commonly used partition types.
 .Ic boot
 .Op Fl b Ar pmbr
 .Op Fl g Ar gptboot
+.Op Fl i Ar index
 .Op Fl s Ar count
 .Ar device ...
 .Xc
@@ -166,6 +174,11 @@ option allows the user to specify an alternate path for the GPT boot loader
 that is installed into the boot partition.
 .Pp
 The
+.Fl i Ar index
+option allows the user to specify which (valid) entry in the GPT table is to
+be selected for booting.
+.Pp
+The
 .Fl s Ar count
 option allows the user to specify the size in sectors of the boot partition
 if one does not already exist.