[sysprof] proc: translate paths found in alternate mount namespaces
- From: Christian Hergert <chergert src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [sysprof] proc: translate paths found in alternate mount namespaces
- Date: Mon, 27 Feb 2017 01:06:48 +0000 (UTC)
commit 5a3ebeaa6f6a1d0ac772a54f746f29f52c07de52
Author: Christian Hergert <chergert redhat com>
Date: Sun Feb 26 16:59:48 2017 -0800
proc: translate paths found in alternate mount namespaces
If we come across a map that is in another namespace, we might need to
translate it to the filesystem/path inside that mount namespace. Otherwise,
we won't be able to accurately decode ELF symbols due to loading the
incorrect binary/debug files.
lib/sp-proc-source.c | 178 ++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 174 insertions(+), 4 deletions(-)
---
diff --git a/lib/sp-proc-source.c b/lib/sp-proc-source.c
index efe7093..a3e5024 100644
--- a/lib/sp-proc-source.c
+++ b/lib/sp-proc-source.c
@@ -151,11 +151,154 @@ sp_proc_source_populate_process (SpProcSource *self,
}
}
+static gboolean
+strv_at_least_len (GStrv strv,
+ guint len)
+{
+ for (guint i = 0; i < len; i++)
+ {
+ if (strv[i] == NULL)
+ return FALSE;
+ }
+
+ return TRUE;
+}
+
+static gchar *
+find_mount (GStrv mounts,
+ const gchar *mount)
+{
+ gsize len = strlen (mount);
+
+ for (guint i = 0; mounts[i]; i++)
+ {
+ const gchar *endptr;
+ const gchar *begin;
+
+ if (!g_str_has_prefix (mounts[i], mount))
+ continue;
+
+ if (mounts[i][len] != ' ')
+ continue;
+
+ begin = &mounts[i][len + 1];
+ endptr = strchr (begin, ' ');
+ if (endptr == NULL)
+ continue;
+
+ return g_strndup (begin, endptr - begin);
+ }
+
+ return NULL;
+}
+
+/**
+ * sp_proc_source_translate_path:
+ * @file: the path to the file inside target mount namespace
+ * @mountinfo: mount info to locate translated path
+ * @out_file: (out): location for the translated path
+ * @out_file_len: length of @out_file
+ *
+ * This function will use @mountinfo to locate the longest common prefix
+ * to determine which mount contains @file. That will be used to translate
+ * the path pointed to by @file into the host namespace.
+ *
+ * The result is stored in @out_file and will always be NULL terminated.
+ */
+static void
+sp_proc_source_translate_path (const gchar *file,
+ GStrv mountinfo,
+ GStrv mounts,
+ gchar *out_file,
+ gsize out_file_len)
+{
+ g_autofree gchar *closest_host = NULL;
+ g_autofree gchar *closest_guest = NULL;
+ g_autofree gchar *closest_mount = NULL;
+ gsize closest_len = 0;
+
+ g_assert (file != NULL);
+ g_assert (g_str_has_prefix (file, "/newroot/"));
+ g_assert (mountinfo != NULL);
+ g_assert (out_file != NULL);
+
+ if (!g_str_has_prefix (file, "/newroot/"))
+ goto failure;
+
+ file += strlen ("/newroot");
+
+ for (guint i = 0; mountinfo[i] != NULL; i++)
+ {
+ g_auto(GStrv) parts = g_strsplit (mountinfo[i], " ", 11);
+ const gchar *host;
+ const gchar *guest;
+ const gchar *mount;
+
+ /*
+ * Not ideal to do the string split here, but it is much easier
+ * to just do that until we get this right, and then improve
+ * things later when a strok()/etc parser.
+ */
+
+ if (!strv_at_least_len (parts, 10))
+ continue;
+
+ host = parts[3];
+ guest = parts[4];
+ mount = parts[9];
+
+ if (g_str_has_prefix (file, guest))
+ {
+ gsize len = strlen (guest);
+
+ if (len > closest_len && (file[len] == '\0' || file[len] == '/'))
+ {
+ g_free (closest_host);
+ g_free (closest_guest);
+ g_free (closest_mount);
+
+ closest_guest = g_strdup (guest);
+ closest_host = g_strdup (host);
+ closest_mount = g_strdup (mount);
+
+ closest_len = len;
+ }
+ }
+ }
+
+ if (closest_len > 0)
+ {
+ /*
+ * The translated path is relative to the mount. So we need to add that
+ * prefix to this as well, based on matching it from the closest_mount.
+ */
+ g_autofree gchar *mount = NULL;
+
+ mount = find_mount (mounts, closest_mount);
+
+ if (mount != NULL)
+ {
+ g_autofree gchar *path = NULL;
+
+ path = g_build_filename (mount, closest_host, file + strlen (closest_guest), NULL);
+ g_strlcpy (out_file, path, out_file_len);
+
+ return;
+ }
+ }
+
+failure:
+ /* Fallback to just copying the source */
+ g_strlcpy (out_file, file, out_file_len);
+}
+
static void
sp_proc_source_populate_maps (SpProcSource *self,
- GPid pid)
+ GPid pid,
+ GStrv mounts)
{
g_auto(GStrv) lines = NULL;
+ g_auto(GStrv) mountinfo = NULL;
guint i;
g_assert (SP_IS_PROC_SOURCE (self));
@@ -164,9 +307,14 @@ sp_proc_source_populate_maps (SpProcSource *self,
if (NULL == (lines = proc_readlines ("/proc/%d/maps", pid)))
return;
+ if (NULL == (mountinfo = proc_readlines ("/proc/%d/mountinfo", pid)))
+ return;
+
for (i = 0; lines [i] != NULL; i++)
{
gchar file[256];
+ gchar translated[256];
+ const gchar *fileptr = file;
gulong start;
gulong end;
gulong offset;
@@ -197,6 +345,24 @@ sp_proc_source_populate_maps (SpProcSource *self,
inode = 0;
}
+ if (g_str_has_prefix (file, "/newroot/"))
+ {
+ /*
+ * If this file starts with /newroot/, then it is in a different
+ * mount-namespace from our profiler process. This means that we need
+ * to translate the filename to the real path on disk inside our
+ * (hopefully the default) mount-namespace. To do this, we have to
+ * look at /proc/$pid/mountinfo to locate the longest-common-prefix
+ * for the path.
+ */
+ sp_proc_source_translate_path (file,
+ mountinfo,
+ mounts,
+ translated,
+ sizeof translated);
+ fileptr = translated;
+ }
+
sp_capture_writer_add_map (self->writer,
SP_CAPTURE_CURRENT_TIME,
-1,
@@ -205,18 +371,22 @@ sp_proc_source_populate_maps (SpProcSource *self,
end,
offset,
inode,
- file);
+ fileptr);
}
}
static void
sp_proc_source_populate (SpProcSource *self)
{
+ g_auto(GStrv) mounts = NULL;
const gchar *name;
GDir *dir;
g_assert (SP_IS_PROC_SOURCE (self));
+ if (NULL == (mounts = proc_readlines ("/proc/mounts")))
+ return;
+
if (self->pids->len > 0)
{
guint i;
@@ -226,7 +396,7 @@ sp_proc_source_populate (SpProcSource *self)
GPid pid = g_array_index (self->pids, GPid, i);
sp_proc_source_populate_process (self, pid);
- sp_proc_source_populate_maps (self, pid);
+ sp_proc_source_populate_maps (self, pid, mounts);
}
return;
@@ -245,7 +415,7 @@ sp_proc_source_populate (SpProcSource *self)
continue;
sp_proc_source_populate_process (self, pid);
- sp_proc_source_populate_maps (self, pid);
+ sp_proc_source_populate_maps (self, pid, mounts);
}
g_dir_close (dir);
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