pasta: Allow specifying paths and names of namespaces

Based on a patch from Giuseppe Scrivano, this adds the ability to:

- specify paths and names of target namespaces to join, instead of
  a PID, also for user namespaces, with --userns

- request to join or create a network namespace only, without
  entering or creating a user namespace, with --netns-only

- specify the base directory for netns mountpoints, with --nsrun-dir

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
[sbrivio: reworked logic to actually join the given namespaces when
 they're not created, implemented --netns-only and --nsrun-dir,
 updated pasta demo script and man page]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 24 insertions, 6 deletions

diff --git a/passt.1 b/passt.1
index d3a5cc5..b21333b 100644
--- a/passt.1
+++ b/passt.1
@@ -12,7 +12,7 @@
 [\fIOPTION\fR]...
 .br
 .B pasta
-[\fIOPTION\fR]... [\fITARGET_PID\fR]
+[\fIOPTION\fR]... [\fIPID\fR|\fIPATH\fR|\fINAME\fR]
 
 .SH DESCRIPTION
 
@@ -56,11 +56,10 @@ or with the \fBqrap\fR(1) wrapper.
 equivalent functionality to network namespaces, as the one offered by
 \fBpasst\fR for virtual machines.
 
-If TARGET_PID is given, \fBpasta\fR associates to the user and network namespace
-of the corresponding process. Otherwise, \fBpasta\fR creates a new user and
-network namespace, and spawns an interactive shell within this context. A
-\fItap\fR device within the network namespace is created to provide network
-connectivity.
+If PID, PATH or NAME are given, \fBpasta\fR associates to an existing user and
+network namespace. Otherwise, \fBpasta\fR creates a new user and network
+namespace, and spawns an interactive shell within this context. A \fItap\fR
+device within the network namespace is created to provide network connectivity.
 
 For local TCP and UDP traffic only, \fBpasta\fR also implements a bypass path
 directly mapping Layer-4 sockets between \fIinit\fR and target namespaces,
@@ -357,6 +356,25 @@ Configure UDP port forwarding from target namespace to init namespace.
 
 Default is \fBauto\fR.
 
+.TP
+.BR \-\-userns " " \fIspec
+Target user namespace to join, as path or name (i.e. suffix for --nsrun-dir). If
+PID is given, without this option, the user namespace will be the one of the
+corresponding process.
+
+This option requires PID, PATH or NAME to be specified.
+
+.TP
+.BR \-\-netns-only
+Join or create only the network namespace, not a user namespace. This is implied
+if PATH or NAME are given without \-\-userns.
+
+.TP
+.BR \-\-nsrun-dir " " \fIpath
+Directory for nsfs mountpoints, used as path prefix for names of namespaces.
+
+The default path is shown with --help.
+
 .SH EXAMPLES
 
 .SS \fBpasta