Fix ProcStat::is_stale for gone PIDs

Modify ProcStat::getinode_ to properly report error instead of returning
-1 (which does not work, since its return type ino_t is unsigned).

This enables ProcStat::is_stale to correctly report false when the PID is
gone, as intended in commit 552f4c6.

src/cc/bcc_syms.cc

@@ -34,18 +34,24 @@
 
 #include "syms.h"
 
-ino_t ProcStat::getinode_() {
+bool ProcStat::getinode_(ino_t &inode) {
  struct stat s;
- return (!stat(procfs_.c_str(), &s)) ? s.st_ino : -1;
+ if (!stat(procfs_.c_str(), &s)) {
+ inode = s.st_ino;
+ return true;
+ } else {
+ return false;
+ }
 }
 
 bool ProcStat::is_stale() {
- ino_t cur_inode = getinode_();
- return (cur_inode > 0) && (cur_inode != inode_);
+ ino_t cur_inode;
+ return getinode_(cur_inode) && (cur_inode != inode_);
 }
 
-ProcStat::ProcStat(int pid)
- : procfs_(tfm::format("/proc/%d/exe", pid)), inode_(getinode_()) {}
+ProcStat::ProcStat(int pid) : procfs_(tfm::format("/proc/%d/exe", pid)) {
+ getinode_(inode_);
+}
 
 void KSyms::_add_symbol(const char *symname, const char *modname, uint64_t addr, void *p) {
  KSyms *ks = static_cast<KSyms *>(p);

src/cc/syms.h

@@ -30,12 +30,12 @@
 class ProcStat {
  std::string procfs_;
  ino_t inode_;
- ino_t getinode_();
+ bool getinode_(ino_t &inode);
 
-public:
+ public:
  ProcStat(int pid);
  bool is_stale();
- void reset() { inode_ = getinode_(); }
+ void reset() { getinode_(inode_); }
 };
 
 class SymbolCache {