diff --git a/src/cache.cpp b/src/cache.cpp
index 9dbb768..593760a 100644
--- a/src/cache.cpp
+++ b/src/cache.cpp
@@ -334,7 +334,7 @@ bool StatCache::IsNoObjectCache(const std::string& key, bool overcheck)
     return false;
 }
 
-bool StatCache::AddStat(const std::string& key, headers_t& meta, bool forcedir, bool no_truncate)
+bool StatCache::AddStat(const std::string& key, const headers_t& meta, bool forcedir, bool no_truncate)
 {
     if(!no_truncate && CacheSize< 1){
         return true;
@@ -372,7 +372,7 @@ bool StatCache::AddStat(const std::string& key, headers_t& meta, bool forcedir,
     ent->meta.clear();
     SetStatCacheTime(ent->cache_date);    // Set time.
     //copy only some keys
-    for(headers_t::iterator iter = meta.begin(); iter != meta.end(); ++iter){
+    for(headers_t::const_iterator iter = meta.begin(); iter != meta.end(); ++iter){
         std::string tag   = lower(iter->first);
         std::string value = iter->second;
         if(tag == "content-type"){
diff --git a/src/cache.h b/src/cache.h
index 3c25174..43798f6 100644
--- a/src/cache.h
+++ b/src/cache.h
@@ -163,7 +163,7 @@ class StatCache
         bool AddNoObjectCache(const std::string& key);
 
         // Add stat cache
-        bool AddStat(const std::string& key, headers_t& meta, bool forcedir = false, bool no_truncate = false);
+        bool AddStat(const std::string& key, const headers_t& meta, bool forcedir = false, bool no_truncate = false);
 
         // Update meta stats
         bool UpdateMetaStats(const std::string& key, headers_t& meta);
diff --git a/src/curl.cpp b/src/curl.cpp
index cdf29e5..f10e8d1 100644
--- a/src/curl.cpp
+++ b/src/curl.cpp
@@ -1988,7 +1988,7 @@ bool S3fsCurl::SetUseAhbe(bool ahbe)
     return old;
 }
 
-bool S3fsCurl::GetResponseCode(long& responseCode, bool from_curl_handle)
+bool S3fsCurl::GetResponseCode(long& responseCode, bool from_curl_handle) const
 {
     responseCode = -1;
 
diff --git a/src/curl.h b/src/curl.h
index d3f1b0b..173681e 100644
--- a/src/curl.h
+++ b/src/curl.h
@@ -339,7 +339,7 @@ class S3fsCurl
         bool GetIAMCredentials(const char* cred_url, const char* iam_v2_token, const char* ibm_secret_access_key, std::string& response);
         bool GetIAMRoleFromMetaData(const char* cred_url, const char* iam_v2_token, std::string& token);
         bool AddSseRequestHead(sse_type_t ssetype, const std::string& ssevalue, bool is_only_c, bool is_copy);
-        bool GetResponseCode(long& responseCode, bool from_curl_handle = true);
+        bool GetResponseCode(long& responseCode, bool from_curl_handle = true) const;
         int RequestPerform(bool dontAddAuthHeaders=false);
         int DeleteRequest(const char* tpath);
         int GetIAMv2ApiToken(const char* token_url, int token_ttl, const char* token_ttl_hdr, std::string& response);
@@ -371,9 +371,9 @@ class S3fsCurl
         std::string GetSpecialSavedPath() const { return saved_path; }
         std::string GetUrl() const { return url; }
         std::string GetOp() const { return op; }
-        headers_t* GetResponseHeaders() { return &responseHeaders; }
-        BodyData* GetBodyData() { return &bodydata; }
-        BodyData* GetHeadData() { return &headdata; }
+        const headers_t* GetResponseHeaders() const { return &responseHeaders; }
+        const BodyData* GetBodyData() const { return &bodydata; }
+        const BodyData* GetHeadData() const { return &headdata; }
         CURLcode GetCurlCode() const { return curlCode; }
         long GetLastResponseCode() const { return LastResponseCode; }
         bool SetUseAhbe(bool ahbe);
diff --git a/src/curl_multi.h b/src/curl_multi.h
index 003f22c..c2d62da 100644
--- a/src/curl_multi.h
+++ b/src/curl_multi.h
@@ -62,7 +62,7 @@ class S3fsMultiCurl
         explicit S3fsMultiCurl(int maxParallelism);
         ~S3fsMultiCurl();
 
-        int GetMaxParallelism() { return maxParallelism; }
+        int GetMaxParallelism() const { return maxParallelism; }
 
         S3fsMultiSuccessCallback SetSuccessCallback(S3fsMultiSuccessCallback function);
         S3fsMultiNotFoundCallback SetNotFoundCallback(S3fsMultiNotFoundCallback function);
diff --git a/src/curl_util.h b/src/curl_util.h
index 5567c1b..9fc6b14 100644
--- a/src/curl_util.h
+++ b/src/curl_util.h
@@ -28,7 +28,6 @@ class sse_type_t;
 //----------------------------------------------
 // Functions
 //----------------------------------------------
-std::string GetContentMD5(int fd);
 struct curl_slist* curl_slist_sort_insert(struct curl_slist* list, const char* data);
 struct curl_slist* curl_slist_sort_insert(struct curl_slist* list, const char* key, const char* value);
 struct curl_slist* curl_slist_remove(struct curl_slist* list, const char* key);
diff --git a/src/fdcache_entity.cpp b/src/fdcache_entity.cpp
index 912a264..c205988 100644
--- a/src/fdcache_entity.cpp
+++ b/src/fdcache_entity.cpp
@@ -196,7 +196,7 @@ void FdEntity::Clear()
 // The return value is the same as the class method GetInode().
 // The caller must have exclusive control.
 //
-ino_t FdEntity::GetInode()
+ino_t FdEntity::GetInode() const
 {
     if(cachepath.empty()){
         S3FS_PRN_INFO("cache file path is empty, then return inode as 0.");
@@ -298,7 +298,7 @@ int FdEntity::OpenPseudoFd(int flags, AutoLock::Type locktype)
     return pseudo_fd;
 }
 
-int FdEntity::GetOpenCount(AutoLock::Type locktype)
+int FdEntity::GetOpenCount(AutoLock::Type locktype) const
 {
     AutoLock auto_lock(&fdent_lock, locktype);
 
@@ -362,7 +362,7 @@ int FdEntity::OpenMirrorFile()
     return mirrorfd;
 }
 
-bool FdEntity::FindPseudoFd(int fd, AutoLock::Type locktype)
+bool FdEntity::FindPseudoFd(int fd, AutoLock::Type locktype) const
 {
     AutoLock auto_lock(&fdent_lock, locktype);
 
@@ -777,7 +777,7 @@ bool FdEntity::IsModified() const
     return pagelist.IsModified();
 }
 
-bool FdEntity::GetStats(struct stat& st, AutoLock::Type locktype)
+bool FdEntity::GetStats(struct stat& st, AutoLock::Type locktype) const
 {
     AutoLock auto_lock(&fdent_lock, locktype);
     if(-1 == physical_fd){
@@ -976,7 +976,7 @@ bool FdEntity::ClearHoldingMtime(AutoLock::Type locktype)
     return true;
 }
 
-bool FdEntity::GetSize(off_t& size)
+bool FdEntity::GetSize(off_t& size) const
 {
     AutoLock auto_lock(&fdent_lock);
     if(-1 == physical_fd){
@@ -988,7 +988,7 @@ bool FdEntity::GetSize(off_t& size)
     return true;
 }
 
-bool FdEntity::GetXattr(std::string& xattr)
+bool FdEntity::GetXattr(std::string& xattr) const
 {
     AutoLock auto_lock(&fdent_lock);
 
@@ -2531,7 +2531,7 @@ bool FdEntity::AddUntreated(off_t start, off_t size)
     return result;
 }
 
-bool FdEntity::GetLastUpdateUntreatedPart(off_t& start, off_t& size)
+bool FdEntity::GetLastUpdateUntreatedPart(off_t& start, off_t& size) const
 {
     // Get last untreated area
     if(!untreated_list.GetLastUpdatePart(start, size)){
diff --git a/src/fdcache_entity.h b/src/fdcache_entity.h
index 110aa92..7a88134 100644
--- a/src/fdcache_entity.h
+++ b/src/fdcache_entity.h
@@ -49,7 +49,7 @@ class FdEntity
         static bool     mixmultipart;   // whether multipart uploading can use copy api.
         static bool     streamupload;   // whether stream uploading.
 
-        pthread_mutex_t fdent_lock;
+        mutable pthread_mutex_t fdent_lock;
         bool            is_lock_init;
         std::string     path;           // object path
         int             physical_fd;    // physical file(cache or temporary file) descriptor
@@ -73,7 +73,7 @@ class FdEntity
         static ino_t GetInode(int fd);
 
         void Clear();
-        ino_t GetInode();
+        ino_t GetInode() const;
         int OpenMirrorFile();
         int NoCacheLoadAndPost(PseudoFdInfo* pseudo_obj, off_t start = 0, off_t size = 0);  // size=0 means loading to end
         PseudoFdInfo* CheckPseudoFdFlags(int fd, bool writable, AutoLock::Type locktype = AutoLock::NONE);
@@ -105,12 +105,12 @@ class FdEntity
 
         void Close(int fd);
         bool IsOpen() const { return (-1 != physical_fd); }
-        bool FindPseudoFd(int fd, AutoLock::Type locktype = AutoLock::NONE);
+        bool FindPseudoFd(int fd, AutoLock::Type locktype = AutoLock::NONE) const;
         int Open(const headers_t* pmeta, off_t size, const struct timespec& ts_mctime, int flags, AutoLock::Type type);
         bool LoadAll(int fd, headers_t* pmeta = NULL, off_t* size = NULL, bool force_load = false);
         int Dup(int fd, AutoLock::Type locktype = AutoLock::NONE);
         int OpenPseudoFd(int flags = O_RDONLY, AutoLock::Type locktype = AutoLock::NONE);
-        int GetOpenCount(AutoLock::Type locktype = AutoLock::NONE);
+        int GetOpenCount(AutoLock::Type locktype = AutoLock::NONE) const;
         const char* GetPath() const { return path.c_str(); }
         bool RenamePath(const std::string& newpath, std::string& fentmapkey);
         int GetPhysicalFd() const { return physical_fd; }
@@ -118,7 +118,7 @@ class FdEntity
         bool MergeOrgMeta(headers_t& updatemeta);
         int UploadPending(int fd, AutoLock::Type type);
 
-        bool GetStats(struct stat& st, AutoLock::Type locktype = AutoLock::NONE);
+        bool GetStats(struct stat& st, AutoLock::Type locktype = AutoLock::NONE) const;
         int SetCtime(struct timespec time, AutoLock::Type locktype = AutoLock::NONE);
         int SetAtime(struct timespec time, AutoLock::Type locktype = AutoLock::NONE);
         int SetMCtime(struct timespec mtime, struct timespec ctime, AutoLock::Type locktype = AutoLock::NONE);
@@ -128,8 +128,8 @@ class FdEntity
         bool UpdateMCtime();
         bool SetHoldingMtime(struct timespec mtime, AutoLock::Type locktype = AutoLock::NONE);
         bool ClearHoldingMtime(AutoLock::Type locktype = AutoLock::NONE);
-        bool GetSize(off_t& size);
-        bool GetXattr(std::string& xattr);
+        bool GetSize(off_t& size) const;
+        bool GetXattr(std::string& xattr) const;
         bool SetXattr(const std::string& xattr);
         bool SetMode(mode_t mode);
         bool SetUId(uid_t uid);
@@ -150,7 +150,7 @@ class FdEntity
 
         void MarkDirtyNewFile();
 
-        bool GetLastUpdateUntreatedPart(off_t& start, off_t& size);
+        bool GetLastUpdateUntreatedPart(off_t& start, off_t& size) const;
         bool ReplaceLastUpdateUntreatedPart(off_t front_start, off_t front_size, off_t behind_start, off_t behind_size);
 };
 
diff --git a/src/fdcache_fdinfo.cpp b/src/fdcache_fdinfo.cpp
index c006358..42e30b0 100644
--- a/src/fdcache_fdinfo.cpp
+++ b/src/fdcache_fdinfo.cpp
@@ -302,7 +302,7 @@ bool PseudoFdInfo::GetUploadId(std::string& id) const
     return true;
 }
 
-bool PseudoFdInfo::GetEtaglist(etaglist_t& list)
+bool PseudoFdInfo::GetEtaglist(etaglist_t& list) const
 {
     if(!IsUploading()){
         S3FS_PRN_ERR("Multipart Upload has not started yet.");
diff --git a/src/fdcache_fdinfo.h b/src/fdcache_fdinfo.h
index 34a6538..d0ce8f4 100644
--- a/src/fdcache_fdinfo.h
+++ b/src/fdcache_fdinfo.h
@@ -66,7 +66,7 @@ class PseudoFdInfo
         filepart_list_t         upload_list;
         petagpool               etag_entities;      // list of etag string and part number entities(to maintain the etag entity even if MPPART_INFO is destroyed)
         bool                    is_lock_init;
-        pthread_mutex_t         upload_list_lock;   // protects upload_id and upload_list
+        mutable pthread_mutex_t upload_list_lock;   // protects upload_id and upload_list
         Semaphore               uploaded_sem;       // use a semaphore to trigger an upload completion like event flag
         volatile int            instruct_count;     // number of instructions for processing by threads
         volatile int            completed_count;    // number of completed processes by thread
@@ -103,7 +103,7 @@ class PseudoFdInfo
 
         bool IsUploading() const { return !upload_id.empty(); }
         bool GetUploadId(std::string& id) const;
-        bool GetEtaglist(etaglist_t& list);
+        bool GetEtaglist(etaglist_t& list) const;
 
         bool AppendUploadPart(off_t start, off_t size, bool is_copy = false, etagpair** ppetag = NULL);
 
diff --git a/src/fdcache_untreated.cpp b/src/fdcache_untreated.cpp
index c8ac6ee..b646a8c 100644
--- a/src/fdcache_untreated.cpp
+++ b/src/fdcache_untreated.cpp
@@ -99,7 +99,7 @@ bool UntreatedParts::AddPart(off_t start, off_t size)
     return true;
 }
 
-bool UntreatedParts::RowGetPart(off_t& start, off_t& size, off_t max_size, off_t min_size, bool lastpart)
+bool UntreatedParts::RowGetPart(off_t& start, off_t& size, off_t max_size, off_t min_size, bool lastpart) const
 {
     if(max_size <= 0 || min_size < 0 || max_size < min_size){
         S3FS_PRN_ERR("Paramter are wrong(max_size=%lld, min_size=%lld).", static_cast<long long int>(max_size), static_cast<long long int>(min_size));
@@ -108,7 +108,7 @@ bool UntreatedParts::RowGetPart(off_t& start, off_t& size, off_t max_size, off_t
     AutoLock auto_lock(&untreated_list_lock);
 
     // Check the overlap with the existing part and add the part.
-    for(untreated_list_t::iterator iter = untreated_list.begin(); iter != untreated_list.end(); ++iter){
+    for(untreated_list_t::const_iterator iter = untreated_list.begin(); iter != untreated_list.end(); ++iter){
         if(!lastpart || iter->untreated_tag == last_tag){
             if(min_size <= iter->size){
                 if(iter->size <= max_size){
@@ -191,7 +191,7 @@ bool UntreatedParts::ClearParts(off_t start, off_t size)
 //
 // Update the last updated Untreated part
 //
-bool UntreatedParts::GetLastUpdatePart(off_t& start, off_t& size)
+bool UntreatedParts::GetLastUpdatePart(off_t& start, off_t& size) const
 {
     AutoLock auto_lock(&untreated_list_lock);
 
diff --git a/src/fdcache_untreated.h b/src/fdcache_untreated.h
index 3704953..355c02e 100644
--- a/src/fdcache_untreated.h
+++ b/src/fdcache_untreated.h
@@ -30,14 +30,14 @@
 class UntreatedParts
 {
     private:
-        pthread_mutex_t  untreated_list_lock;   // protects untreated_list
+        mutable pthread_mutex_t untreated_list_lock;   // protects untreated_list
         bool             is_lock_init;
 
         untreated_list_t untreated_list;
         long             last_tag;              // [NOTE] Use this to identify the latest updated part.
 
     private:
-        bool RowGetPart(off_t& start, off_t& size, off_t max_size, off_t min_size, bool lastpart);
+        bool RowGetPart(off_t& start, off_t& size, off_t max_size, off_t min_size, bool lastpart) const;
 
     public:
         UntreatedParts();
@@ -46,12 +46,12 @@ class UntreatedParts
         bool empty();
 
         bool AddPart(off_t start, off_t size);
-        bool GetLastUpdatedPart(off_t& start, off_t& size, off_t max_size, off_t min_size = MIN_MULTIPART_SIZE) { return RowGetPart(start, size, max_size, min_size, true); }
+        bool GetLastUpdatedPart(off_t& start, off_t& size, off_t max_size, off_t min_size = MIN_MULTIPART_SIZE) const { return RowGetPart(start, size, max_size, min_size, true); }
 
         bool ClearParts(off_t start, off_t size);
         bool ClearAll() { return ClearParts(0, 0); }
 
-        bool GetLastUpdatePart(off_t& start, off_t& size);
+        bool GetLastUpdatePart(off_t& start, off_t& size) const;
         bool ReplaceLastUpdatePart(off_t start, off_t size);
         bool RemoveLastUpdatePart();
 
diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index 170ea6f..e9141df 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -3112,7 +3112,7 @@ static int list_bucket(const char* path, S3ObjList& head, const char* delimiter,
             S3FS_PRN_ERR("ListBucketRequest returns with error.");
             return result;
         }
-        BodyData* body = s3fscurl.GetBodyData();
+        const BodyData* body = s3fscurl.GetBodyData();
 
         // xmlDocPtr
         if(NULL == (doc = xmlReadMemory(body->str(), static_cast<int>(body->size()), "", NULL, 0))){
@@ -4037,7 +4037,7 @@ static int s3fs_check_service()
         if(300 <= responseCode && responseCode < 500){
 
             // check region error(for putting message or retrying)
-            BodyData* body = s3fscurl.GetBodyData();
+            const BodyData* body = s3fscurl.GetBodyData();
             std::string expectregion;
             std::string expectendpoint;
             if(check_region_error(body->str(), body->size(), expectregion)){
diff --git a/src/s3fs_cred.cpp b/src/s3fs_cred.cpp
index 0b592d0..78281c4 100644
--- a/src/s3fs_cred.cpp
+++ b/src/s3fs_cred.cpp
@@ -285,7 +285,7 @@ bool S3fsCred::SetAccessKeyWithSessionToken(const char* AccessKeyId, const char*
     return true;
 }
 
-bool S3fsCred::IsSetAccessKeys(AutoLock::Type type)
+bool S3fsCred::IsSetAccessKeys(AutoLock::Type type) const
 {
     AutoLock auto_lock(&token_lock, type);
 
@@ -321,14 +321,14 @@ bool S3fsCred::SetIAMRole(const char* role, AutoLock::Type type)
     return true;
 }
 
-std::string S3fsCred::GetIAMRole(AutoLock::Type type)
+std::string S3fsCred::GetIAMRole(AutoLock::Type type) const
 {
     AutoLock auto_lock(&token_lock, type);
 
     return IAM_role;
 }
 
-bool S3fsCred::IsSetIAMRole(AutoLock::Type type)
+bool S3fsCred::IsSetIAMRole(AutoLock::Type type) const
 {
     AutoLock auto_lock(&token_lock, type);
 
@@ -435,7 +435,7 @@ int S3fsCred::SetIMDSVersion(int version, AutoLock::Type type)
     return old;
 }
 
-int S3fsCred::GetIMDSVersion(AutoLock::Type type)
+int S3fsCred::GetIMDSVersion(AutoLock::Type type) const
 {
     AutoLock auto_lock(&token_lock, type);
 
@@ -455,7 +455,7 @@ bool S3fsCred::SetIAMv2APIToken(const std::string& token, AutoLock::Type type)
     return true;
 }
 
-std::string S3fsCred::GetIAMv2APIToken(AutoLock::Type type)
+std::string S3fsCred::GetIAMv2APIToken(AutoLock::Type type) const
 {
     AutoLock auto_lock(&token_lock, type);
 
@@ -596,7 +596,7 @@ bool S3fsCred::SetIAMRoleFromMetaData(const char* response, AutoLock::Type type)
 //
 // Check passwd file readable
 //
-bool S3fsCred::IsReadableS3fsPasswdFile()
+bool S3fsCred::IsReadableS3fsPasswdFile() const
 {
     if(passwd_file.empty()){
         return false;
diff --git a/src/s3fs_cred.h b/src/s3fs_cred.h
index 32983cc..43e9b76 100644
--- a/src/s3fs_cred.h
+++ b/src/s3fs_cred.h
@@ -53,7 +53,7 @@ class S3fsCred
 
         static std::string  bucket_name;
 
-        pthread_mutex_t     token_lock;
+        mutable pthread_mutex_t token_lock;
         bool                is_lock_init;
 
         std::string         passwd_file;
@@ -104,7 +104,7 @@ class S3fsCred
 
         bool SetAccessKey(const char* AccessKeyId, const char* SecretAccessKey, AutoLock::Type type);
         bool SetAccessKeyWithSessionToken(const char* AccessKeyId, const char* SecretAccessKey, const char * SessionToken, AutoLock::Type type);
-        bool IsSetAccessKeys(AutoLock::Type type);
+        bool IsSetAccessKeys(AutoLock::Type type) const;
 
         bool SetIsECS(bool flag);
         bool SetIsUseSessionToken(bool flag);
@@ -112,20 +112,20 @@ class S3fsCred
         bool SetIsIBMIAMAuth(bool flag);
 
         int SetIMDSVersion(int version, AutoLock::Type type);
-        int GetIMDSVersion(AutoLock::Type type);
+        int GetIMDSVersion(AutoLock::Type type) const;
 
         bool SetIAMv2APIToken(const std::string& token, AutoLock::Type type);
-        std::string GetIAMv2APIToken(AutoLock::Type type);
+        std::string GetIAMv2APIToken(AutoLock::Type type) const;
 
         bool SetIAMRole(const char* role, AutoLock::Type type);
-        std::string GetIAMRole(AutoLock::Type type);
-        bool IsSetIAMRole(AutoLock::Type type);
+        std::string GetIAMRole(AutoLock::Type type) const;
+        bool IsSetIAMRole(AutoLock::Type type) const;
         size_t SetIAMFieldCount(size_t field_count);
         std::string SetIAMCredentialsURL(const char* url);
         std::string SetIAMTokenField(const char* token_field);
         std::string SetIAMExpiryField(const char* expiry_field);
 
-        bool IsReadableS3fsPasswdFile();
+        bool IsReadableS3fsPasswdFile() const;
         bool CheckS3fsPasswdFilePerms();
         bool ParseS3fsPasswdFile(bucketkvmap_t& resmap);
         bool ReadS3fsPasswdFile(AutoLock::Type type);
diff --git a/src/threadpoolman.cpp b/src/threadpoolman.cpp
index 1696e6c..a4a0142 100644
--- a/src/threadpoolman.cpp
+++ b/src/threadpoolman.cpp
@@ -177,7 +177,7 @@ ThreadPoolMan::~ThreadPoolMan()
     }
 }
 
-bool ThreadPoolMan::IsExit()
+bool ThreadPoolMan::IsExit() const
 {
     AutoLock auto_lock(&thread_exit_flag_lock);
     return is_exit;
diff --git a/src/threadpoolman.h b/src/threadpoolman.h
index fdd3a3d..4a00551 100644
--- a/src/threadpoolman.h
+++ b/src/threadpoolman.h
@@ -70,7 +70,7 @@ class ThreadPoolMan
         thpoolman_params_t    instruction_list;
 
         bool                  is_exit_flag_init;
-        pthread_mutex_t       thread_exit_flag_lock;
+        mutable pthread_mutex_t thread_exit_flag_lock;
 
     private:
         static void* Worker(void* arg);
@@ -78,7 +78,7 @@ class ThreadPoolMan
         explicit ThreadPoolMan(int count = 1);
         ~ThreadPoolMan();
 
-        bool IsExit();
+        bool IsExit() const;
         void SetExitFlag(bool exit_flag);
 
         bool StopThreads();