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

gpt.8

 .\" Copyright (c) 2002 Marcel Moolenaar
 .\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\"
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 65 matching lines @@
 .Fl r
 option causes the
 .Nm
 utility to open the device for reading only.
 Currently this option is primarily useful for the
 .Ic show
 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.
 There is no formalized definition of the different levels yet.
 .Ss Commands
 .Bl -tag -width indent
 .\" ==== add ====
 .It Xo
 .Nm
 .Ic add
@@ skipping 37 matching lines @@
 .Cm boot , efi , swap , ufs , zfs , hfs , linux
 and
 .Cm windows
 as aliases for the most commonly used partition types.
 .\" ==== boot ====
 .It Xo
 .Nm
 .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
 The
 .Ic boot
 command allows the user to make a GPT labeled disk bootable via the BIOS
 bootstrap on i386 and amd64 machines.
 By default,
 the
 .Pa /boot/pmbr
 boot loader is installed into the PMBR and the
 .Pa /boot/gptboot
 boot loader is installed into the first boot partition.
 If no boot partition exists and there is available space,
 a boot partition will be created.
 .Pp
 The
 .Fl b Ar pmbr
 option allows the user to specify an alternate path for the PMBR boot loader.
 .Pp
 The
 .Fl g Ar gptboot
 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.
 A boot partition must be at least 16 kilobytes.
 By default,
 a size of 64 kilobytes is used.
 Note that the PMBR boot loader will load the entire boot partition into
 memory.
 As a result, the boot partition may not exceed 545 kilobytes.
 .\" ==== create ====
@@ skipping 188 matching lines @@
 .Fl p Ar count
 option may be changed to a command option rather than a generic option.
 There are only two commands that use it so there is a chance that the natural
 tendency for people is to use it as a command option.
 Also, options primarily intended for diagnostic or debug purposes may be
 removed in future versions.
 .Pp
 Another possibility is that the current usage model is accompanied by
 other interfaces to make the tool usable as a back-end.
 This all depends on demand and thus feedback.