perf symbols: Find symbols in different mount namespace

Teach perf how to resolve symbols from binaries that are in a different
mount namespace from the tool.  This allows perf to generate meaningful
stack traces even if the binary resides in a different mount namespace
from the tool.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Tested-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1499305693-1599-2-git-send-email-kjlx@templeofstupid.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 127 insertions, 0 deletions

diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
index 67dcbcc73c7d..bcc6bb19cf10 100644
--- a/tools/perf/util/namespaces.c
+++ b/tools/perf/util/namespaces.c
@@ -9,9 +9,13 @@
 #include "namespaces.h"
 #include "util.h"
 #include "event.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sched.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 struct namespaces *namespaces__new(struct namespaces_event *event)
 {
@@ -35,3 +39,126 @@ void namespaces__free(struct namespaces *namespaces)
 {
         free(namespaces);
 }
+
+void nsinfo__init(struct nsinfo *nsi)
+{
+        char oldns[PATH_MAX];
+        char *newns = NULL;
+        struct stat old_stat;
+        struct stat new_stat;
+
+        if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+                return;
+
+        if (asprintf(&newns, "/proc/%d/ns/mnt", nsi->pid) == -1)
+                return;
+
+        if (stat(oldns, &old_stat) < 0)
+                goto out;
+
+        if (stat(newns, &new_stat) < 0)
+                goto out;
+
+        /* Check if the mount namespaces differ, if so then indicate that we
+         * want to switch as part of looking up dso/map data.
+         */
+        if (old_stat.st_ino != new_stat.st_ino) {
+                nsi->need_setns = true;
+                nsi->mntns_path = newns;
+                newns = NULL;
+        }
+
+out:
+        free(newns);
+}
+
+struct nsinfo *nsinfo__new(pid_t pid)
+{
+        struct nsinfo *nsi = calloc(1, sizeof(*nsi));
+
+        if (nsi != NULL) {
+                nsi->pid = pid;
+                nsi->need_setns = false;
+                nsinfo__init(nsi);
+                refcount_set(&nsi->refcnt, 1);
+        }
+
+        return nsi;
+}
+
+void nsinfo__delete(struct nsinfo *nsi)
+{
+        zfree(&nsi->mntns_path);
+        free(nsi);
+}
+
+struct nsinfo *nsinfo__get(struct nsinfo *nsi)
+{
+        if (nsi)
+                refcount_inc(&nsi->refcnt);
+        return nsi;
+}
+
+void nsinfo__put(struct nsinfo *nsi)
+{
+        if (nsi && refcount_dec_and_test(&nsi->refcnt))
+                nsinfo__delete(nsi);
+}
+
+void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc)
+{
+        char curpath[PATH_MAX];
+        int oldns = -1;
+        int newns = -1;
+
+        if (nc == NULL)
+                return;
+
+        nc->oldns = -1;
+        nc->newns = -1;
+
+        if (!nsi || !nsi->need_setns)
+                return;
+
+        if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+                return;
+
+        oldns = open(curpath, O_RDONLY);
+        if (oldns < 0)
+                return;
+
+        newns = open(nsi->mntns_path, O_RDONLY);
+        if (newns < 0)
+                goto errout;
+
+        if (setns(newns, CLONE_NEWNS) < 0)
+                goto errout;
+
+        nc->oldns = oldns;
+        nc->newns = newns;
+        return;
+
+errout:
+        if (oldns > -1)
+                close(oldns);
+        if (newns > -1)
+                close(newns);
+}
+
+void nsinfo__mountns_exit(struct nscookie *nc)
+{
+        if (nc == NULL || nc->oldns == -1 || nc->newns == -1)
+                return;
+
+        setns(nc->oldns, CLONE_NEWNS);
+
+        if (nc->oldns > -1) {
+                close(nc->oldns);
+                nc->oldns = -1;
+        }
+
+        if (nc->newns > -1) {
+                close(nc->newns);
+                nc->newns = -1;
+        }
+}