cpud: server: add flags to cpud -remote

[Lencerf]

Currently the cpud server starts commands by executing cpud -remote plus the command string sent from the client. There is no way to start cpud -remote with -d on.

This patch adds -d to cpud -remote if the cpud server is running with -d.

[rminnich]

actually I don't think this is needed.

rminnich@pop-os:~/go/src/github.com/u-root/cpu$ cpu vf2 -d /bbin/elvish
1970/01/01 00:21:02 CPUD(remote):Args [/bbin/cpud -remote -port9p=41841 -d /bbin/elvish] pid 71 *runasinit false *remote true env [SHELL=/bin/bash GTK_IM_MODULE=ibus XMODIFIERS=@im=ibus PWD=/home/rminnich/go/src/github.com/u-root/cpu LOGNAME=rminnich XDG_SESSION_TYPE=tty MOTD_SHOWN=pam HOME=/home/rminnich LANG=en_US=
/tmp/cpu/lib /lib none defaults,bind 0 0
/tmp/cpu/lib64 /lib64 none defaults,bind 0 0
/tmp/cpu/usr /usr none defaults,bind 0 0
/tmp/cpu/bin /bin none defaults,bind 0 0
/tmp/cpu/etc /etc none defaults,bind 0 0
/tmp/cpu/home /home none defaults,bind 0 0
 CPU_TMPMNT=/tmp TERM=ansi]
1970/01/01 00:21:02 CPUD(remote):args ["/bbin/elvish"], port9p 41841
1970/01/01 00:21:02 CPUD(remote):session:call s.NameSpace
1970/01/01 00:21:02 CPUD(remote):session:Dial [::1]:41841
1970/01/01 00:21:02 CPUD(remote):session:Dial [::1]:41841:dial tcp [::1]:41841: connect: connection refused
1970/01/01 00:21:02 CPUD(remote):session:Dial 127.0.0.1:41841
1970/01/01 00:21:02 CPUD(remote):session:Connected: write nonce 19294c6c3f29ccd2d52e1a123ab49e9b

1970/01/01 00:21:02 CPUD(remote):session:Wrote the nonce
1970/01/01 00:21:02 CPUD(remote):session:fd is 9
1970/01/01 00:21:02 CPUD(remote):session:mount 127.0.0.1 on /tmp/cpu 9p 0x6 version=9p2000.L,trans=fd,rfdno=9,wfdno=9,uname=rminnich,debug=0,msize=65536
1970/01/01 00:21:02 CPUD(remote):session:mount done
1970/01/01 00:21:02 CPUD(remote):session:Mounting "\n/tmp/cpu/lib /lib none defaults,bind 0 0\n/tmp/cpu/lib64 /lib64 none defaults,bind 0 0\n/tmp/cpu/usr /usr none defaults,bind 0 0\n/tmp/cpu/bin /bin none defaults,bind 0 0\n/tmp/cpu/etc /etc none defaults,bind 0 0\n/tmp/cpu/home /home none defaults,bind 0 0\n"
1970/01/01 00:21:02 CPUD(remote):session:Terminal ready
1970/01/01 00:21:02 CPUD(remote):session:dropPrives: uid is 0
1970/01/01 00:21:02 CPUD(remote):session:dropPrivs: not dropping privs
1970/01/01 00:21:02 CPUD(remote):session:runRemote: command is []

works fine.

Of course it also means users can set arbitrary options to cpud, which seems ... bad. Possibly we should be filtering them?

[Lencerf]

Of course it also means users can set arbitrary options to cpud, which seems ... bad.

Actually we can even do something likecpu vf2 -remote=false /bbin/elvish and this will make the cpud process starts as a server instead of the remote mode.

From the perspective of a user of the client package, client.Command("vf2", "-d", "/bbin/elvish") looks really strange ...

[rminnich]

We need to figure this out. I realize that looks strange but ... I don't think "looks really strange" is enough to make it unacceptable. The ability for a user to easily enable debugging for a single session is really handy.

[rminnich]

ok, I THINK with the merge of #246, this PR is not needed.
Note that I have fixed the problem changyuan pointed out, above.