expose the GetPidByName API of dumpstate

Bug: 32248316

This API is used by external dumpstate module
1) add unittest for GetPidByName
2) change the API name to c++ style
3) Test: dumpstate_test pass

Change-Id: I5eb80e0d1f1ef0f09b77ac3affd8a9b41d64f679
Signed-off-by: Ecco Park <eccopark@google.com>
diff --git a/cmds/dumpstate/DumpstateUtil.cpp b/cmds/dumpstate/DumpstateUtil.cpp
index 9faa63e..d517797 100644
--- a/cmds/dumpstate/DumpstateUtil.cpp
+++ b/cmds/dumpstate/DumpstateUtil.cpp
@@ -18,6 +18,7 @@
 
 #include "DumpstateUtil.h"
 
+#include <dirent.h>
 #include <fcntl.h>
 #include <sys/prctl.h>
 #include <sys/wait.h>
@@ -25,7 +26,10 @@
 
 #include <vector>
 
+#include <android-base/file.h>
 #include <android-base/properties.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
 #include <cutils/log.h>
 
 #include "DumpstateInternal.h"
@@ -342,3 +346,31 @@
 
     return status;
 }
+
+int GetPidByName(const std::string& ps_name) {
+    DIR* proc_dir;
+    struct dirent* ps;
+    unsigned int pid;
+    std::string cmdline;
+
+    if (!(proc_dir = opendir("/proc"))) {
+        MYLOGE("Can't open /proc\n");
+        return -1;
+    }
+
+    while ((ps = readdir(proc_dir))) {
+        if (!(pid = atoi(ps->d_name))) {
+            continue;
+        }
+        android::base::ReadFileToString("/proc/" + std::string(ps->d_name) + "/cmdline", &cmdline);
+        if (cmdline.find(ps_name) == std::string::npos) {
+            continue;
+        } else {
+            closedir(proc_dir);
+            return pid;
+        }
+    }
+    MYLOGE("can't find the pid\n");
+    closedir(proc_dir);
+    return -1;
+}