perf probe: Allow placing uprobes in alternate namespaces.

Teaches perf how to place a uprobe on a file that's in a different mount
namespace.  The user must add the probe using the --target-ns argument
to perf probe.  Once it has been placed, it may be recorded against
without further namespace-specific commands.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
[ PPC build fixed by Ravi: ]
Link: http://lkml.kernel.org/r/1500287542-6219-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
[ Fix !HAVE_DWARF_SUPPORT build ]
Link: http://lkml.kernel.org/r/1499305693-1599-4-git-send-email-kjlx@templeofstupid.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-probe.txt

@@ -130,6 +130,11 @@ OPTIONS
 --max-probes=NUM::
 	Set the maximum number of probe points for an event. Default is 128.
 
+--target-ns=PID:
+	Obtain mount namespace information from the target pid.  This is
+	used when creating a uprobe for a process that resides in a
+	different mount namespace from the perf(1) utility.
+
 -x::
 --exec=PATH::
 	Specify path to the executable or shared library file for user
@@ -264,6 +269,10 @@ Add probes at malloc() function on libc
 
  ./perf probe -x /lib/libc.so.6 malloc or ./perf probe /lib/libc.so.6 malloc
 
+Add a uprobe to a target process running in a different mount namespace
+
+ ./perf probe --target-ns <target pid> -x /lib64/libc.so.6 malloc
+
 SEE ALSO
 --------
 linkperf:perf-trace[1], linkperf:perf-record[1], linkperf:perf-buildid-cache[1]

tools/perf/arch/powerpc/util/sym-handling.c

@@ -126,7 +126,7 @@ void arch__post_process_probe_trace_events(struct perf_probe_event *pev,
 	struct rb_node *tmp;
 	int i = 0;
 
-	map = get_target_map(pev->target, pev->uprobes);
+	map = get_target_map(pev->target, pev->nsi, pev->uprobes);
 	if (!map || map__load(map) < 0)
 		return;
 

tools/perf/builtin-probe.c

@@ -58,6 +58,7 @@ static struct {
 	struct line_range line_range;
 	char *target;
 	struct strfilter *filter;
+	struct nsinfo *nsi;
 } params;
 
 /* Parse an event definition. Note that any error must die. */
@@ -80,6 +81,9 @@ static int parse_probe_event(const char *str)
 		params.target_used = true;
 	}
 
+	if (params.nsi)
+		pev->nsi = nsinfo__get(params.nsi);
+
 	/* Parse a perf-probe command into event */
 	ret = parse_perf_probe_command(str, pev);
 	pr_debug("%d arguments\n", pev->nargs);
@@ -189,7 +193,7 @@ static int opt_set_target(const struct option *opt, const char *str,
 
 		/* Expand given path to absolute path, except for modulename */
 		if (params.uprobes || strchr(str, '/')) {
-			tmp = realpath(str, NULL);
+			tmp = nsinfo__realpath(str, params.nsi);
 			if (!tmp) {
 				pr_warning("Failed to get the absolute path of %s: %m\n", str);
 				return ret;
@@ -208,6 +212,34 @@ static int opt_set_target(const struct option *opt, const char *str,
 	return ret;
 }
 
+static int opt_set_target_ns(const struct option *opt __maybe_unused,
+			     const char *str, int unset __maybe_unused)
+{
+	int ret = -ENOENT;
+	pid_t ns_pid;
+	struct nsinfo *nsip;
+
+	if (str) {
+		errno = 0;
+		ns_pid = (pid_t)strtol(str, NULL, 10);
+		if (errno != 0) {
+			ret = -errno;
+			pr_warning("Failed to parse %s as a pid: %s\n", str,
+				   strerror(errno));
+			return ret;
+		}
+		nsip = nsinfo__new(ns_pid);
+		if (nsip && nsip->need_setns)
+			params.nsi = nsinfo__get(nsip);
+		nsinfo__put(nsip);
+
+		ret = 0;
+	}
+
+	return ret;
+}
+
+
 /* Command option callbacks */
 
 #ifdef HAVE_DWARF_SUPPORT
@@ -299,6 +331,7 @@ static void cleanup_params(void)
 	line_range__clear(&params.line_range);
 	free(params.target);
 	strfilter__delete(params.filter);
+	nsinfo__put(params.nsi);
 	memset(&params, 0, sizeof(params));
 }
 
@@ -554,6 +587,8 @@ __cmd_probe(int argc, const char **argv)
 	OPT_BOOLEAN(0, "cache", &probe_conf.cache, "Manipulate probe cache"),
 	OPT_STRING(0, "symfs", &symbol_conf.symfs, "directory",
 		   "Look for files with symbols relative to this directory"),
+	OPT_CALLBACK(0, "target-ns", NULL, "pid",
+		     "target pid for namespace contexts", opt_set_target_ns),
 	OPT_END()
 	};
 	int ret;
@@ -634,15 +669,15 @@ __cmd_probe(int argc, const char **argv)
 			pr_err_with_code("  Error: Failed to show event list.", ret);
 		return ret;
 	case 'F':
-		ret = show_available_funcs(params.target, params.filter,
-					params.uprobes);
+		ret = show_available_funcs(params.target, params.nsi,
+					   params.filter, params.uprobes);
 		if (ret < 0)
 			pr_err_with_code("  Error: Failed to show functions.", ret);
 		return ret;
 #ifdef HAVE_DWARF_SUPPORT
 	case 'L':
 		ret = show_line_range(&params.line_range, params.target,
-				      params.uprobes);
+				      params.nsi, params.uprobes);
 		if (ret < 0)
 			pr_err_with_code("  Error: Failed to show lines.", ret);
 		return ret;

tools/perf/util/namespaces.c

@@ -11,6 +11,7 @@
 #include "event.h"
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <limits.h>
 #include <sched.h>
 #include <stdlib.h>
 #include <stdio.h>
@@ -233,3 +234,15 @@ void nsinfo__mountns_exit(struct nscookie *nc)
 		nc->newns = -1;
 	}
 }
+
+char *nsinfo__realpath(const char *path, struct nsinfo *nsi)
+{
+	char *rpath;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	rpath = realpath(path, NULL);
+	nsinfo__mountns_exit(&nsc);
+
+	return rpath;
+}

tools/perf/util/namespaces.h

@@ -49,6 +49,8 @@ void nsinfo__put(struct nsinfo *nsi);
 void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc);
 void nsinfo__mountns_exit(struct nscookie *nc);
 
+char *nsinfo__realpath(const char *path, struct nsinfo *nsi);
+
 static inline void __nsinfo__zput(struct nsinfo **nsip)
 {
 	if (nsip) {