roots: get rid of common error messages, add more error counters

One very common case is losing a race to open a file that was deleted.
No need to spam the logs with mere ENOENT reports.

Other errors are more significant.  Log those with errno, and
add event counters to record them.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-roots.cc

@@ -588,27 +588,34 @@ BeesRoots::open_root_nocache(uint64_t rootid)
 				auto parent_rootid = i.offset;
 				// BEESLOG("parent_rootid " << parent_rootid << " dirid " << dirid << " name " << name);
 				BEESTRACE("parent_rootid " << parent_rootid << " dirid " << dirid << " name " << name);
+				BEESCOUNT(root_parent_open_try);
 				Fd parent_fd = open_root(parent_rootid);
 				if (!parent_fd) {
 					BEESLOGTRACE("no parent_fd");
+					BEESCOUNT(root_parent_open_fail);
 					continue;
 				}
+				BEESCOUNT(root_parent_open_ok);
 
 				if (dirid != BTRFS_FIRST_FREE_OBJECTID) {
 					BEESTRACE("dirid " << dirid << " root " << rootid << " INO_PATH");
 					BtrfsIoctlInoPathArgs ino(dirid);
 					if (!ino.do_ioctl_nothrow(parent_fd)) {
-						BEESLOGINFO("dirid " << dirid << " inode path lookup failed in parent_fd " << name_fd(parent_fd));
+						BEESLOGINFO("dirid " << dirid << " inode path lookup failed in parent_fd " << name_fd(parent_fd) << ": " << strerror(errno));
+						BEESCOUNT(root_parent_path_fail);
 						continue;
 					}
 					if (ino.m_paths.empty()) {
 						BEESLOGINFO("dirid " << dirid << " inode has no paths in parent_fd " << name_fd(parent_fd));
+						BEESCOUNT(root_parent_path_empty);
 						continue;
 					}
+					// Theoretically there is only one, so don't bother looping.
 					BEESTRACE("dirid " << dirid << " path " << ino.m_paths.at(0));
 					parent_fd = openat(parent_fd, ino.m_paths.at(0).c_str(), FLAGS_OPEN_DIR);
 					if (!parent_fd) {
 						BEESLOGTRACE("no parent_fd from dirid");
+						BEESCOUNT(root_parent_path_open_fail);
 						continue;
 					}
 				}
@@ -616,17 +623,21 @@ BeesRoots::open_root_nocache(uint64_t rootid)
 				BEESTRACE("openat(" << name_fd(parent_fd) << ", " << name << ")");
 				Fd rv = openat(parent_fd, name.c_str(), FLAGS_OPEN_DIR);
 				if (!rv) {
-					BEESLOGTRACE("open failed for name " << name);
+					BEESLOGTRACE("open failed for name " << name << ": " << strerror(errno));
+					BEESCOUNT(root_open_fail);
 					continue;
 				}
 				BEESCOUNT(root_found);
 
 				// Verify correct root ID
+				// Throw exceptions here because these are very rare events
+				// and unlike the file open case, we don't have alternatives to try
 				auto new_root_id = btrfs_get_root_id(rv);
 				THROW_CHECK2(runtime_error, new_root_id, rootid, new_root_id == rootid);
 				Stat st(rv);
 				THROW_CHECK1(runtime_error, st.st_ino, st.st_ino == BTRFS_FIRST_FREE_OBJECTID);
 				// BEESLOGDEBUG("open_root_nocache " << rootid << ": " << name_fd(rv));
+				BEESCOUNT(root_ok);
 				return rv;
 			}
 		}
@@ -690,6 +701,7 @@ BeesRoots::open_root_ino_nocache(uint64_t root, uint64_t ino)
 
 	Fd root_fd = open_root(root);
 	if (!root_fd) {
+		BEESCOUNT(open_no_root);
 		return root_fd;
 	}
 
@@ -698,7 +710,12 @@ BeesRoots::open_root_ino_nocache(uint64_t root, uint64_t ino)
 	BEESTRACE("looking up ino " << ino);
 	BtrfsIoctlInoPathArgs ipa(ino);
 	if (!ipa.do_ioctl_nothrow(root_fd)) {
+		if (errno == ENOENT) {
+			BEESCOUNT(open_lookup_enoent);
+		} else {
 			BEESLOGINFO("Lookup root " << root << " ino " << ino << " failed: " << strerror(errno));
+			BEESCOUNT(open_lookup_error);
+		}
 		return Fd();
 	}
 
@@ -706,18 +723,26 @@ BeesRoots::open_root_ino_nocache(uint64_t root, uint64_t ino)
 	Fd rv;
 	if (ipa.m_paths.empty()) {
 		BEESLOGWARN("No paths for root " << root << " ino " << ino);
+		BEESCOUNT(open_lookup_empty);
 	}
+	BEESCOUNT(open_lookup_ok);
+
 	for (auto file_path : ipa.m_paths) {
 		BEESTRACE("Looking up root " << root << " ino " << ino << " in dir " << name_fd(root_fd) << " path " << file_path);
 		BEESCOUNT(open_file);
-		// Try to open file RW, fall back to RO
+		// Just open file RO.  root can do the dedup ioctl without
+		// opening in write mode, and if we do open in write mode,
+		// we can't exec the file while we have it open.
 		const char *fp_cstr = file_path.c_str();
 		rv = openat(root_fd, fp_cstr, FLAGS_OPEN_FILE);
 		if (!rv) {
-			BEESCOUNT(open_fail);
+			// errno == ENOENT is the most common error case.
-			// errno == ENOENT is common during snapshot delete, ignore it
+			// No need to report it.
-			if (errno != ENOENT) {
+			if (errno == ENOENT) {
+				BEESCOUNT(open_fail_enoent);
+			} else {
 				BEESLOGWARN("Could not open path '" << file_path << "' at root " << root << " " << name_fd(root_fd) << ": " << strerror(errno));
+				BEESCOUNT(open_fail_error);
 			}
 			continue;
 		}
@@ -783,7 +808,8 @@ BeesRoots::open_root_ino_nocache(uint64_t root, uint64_t ino)
 		return rv;
 	}
 
-	// Odd, we didn't find a path.
+	// All of the paths we tried were wrong.
+	BEESCOUNT(open_no_path);
 	return Fd();
 }