Fixed not to call Flush even if the file size is increased (#1887)

Changed s3fs_truncate function.
This change reduces the number of file uploads if the file size is changed.

On macOS, I have found that the truncate call when "size=0" cannot reflect the file size.(This reason is not understood...)
To avoid this, only when "size=0", the flush method is called as before.

Other than that, I found a bug in FdEntity::Open() and fixed it.

Fixes #1875.

src/fdcache.cpp

@@ -553,6 +553,11 @@ FdEntity* FdManager::Open(int& fd, const char* path, headers_t* pmeta, off_t siz
         // found
         ent = iter->second;
 
+        // [NOTE]
+        // Even if getting the request to change the size of modifying
+        // file to small, we do not change it. Because if it will change,
+        // test_open_second_fd test will be failed.
+        //
         if(ent->IsModified()){
             // If the file is being modified and it's size is larger than size parameter, it will not be resized.
             off_t cur_size = 0;

src/fdcache_entity.cpp

@@ -426,7 +426,7 @@ int FdEntity::Open(const headers_t* pmeta, off_t size, time_t time, int flags, A
         // check only file size(do not need to save cfs and time.
         if(0 <= size && pagelist.Size() != size){
             // truncate temporary file size
-            if(-1 == ftruncate(physical_fd, size)){
+            if(-1 == ftruncate(physical_fd, size) || -1 == fsync(physical_fd)){
                 S3FS_PRN_ERR("failed to truncate temporary file(physical_fd=%d) by errno(%d).", physical_fd, errno);
                 return -errno;
             }
@@ -440,7 +440,7 @@ int FdEntity::Open(const headers_t* pmeta, off_t size, time_t time, int flags, A
         off_t new_size = (0 <= size ? size : size_orgmeta);
         if(pmeta){
             orgmeta  = *pmeta;
-            new_size = get_size(orgmeta);
+            size_orgmeta = get_size(orgmeta);
         }
         if(new_size < size_orgmeta){
             size_orgmeta = new_size;

src/s3fs.cpp

@@ -2168,20 +2168,38 @@ static int s3fs_truncate(const char* _path, off_t size)
 
     // Get file information
     if(0 == (result = get_object_attribute(path, NULL, &meta))){
-        // Exists -> Get file(with size)
+        // File exists
+
+        // [NOTE]
+        // If the file exists, the file has already been opened by FUSE before
+        // truncate is called. Then the call below will change the file size.
+        // (When an already open file is changed the file size, FUSE will not
+        // reopen it.)
+        // The Flush is called before this file is closed, so there is no need
+        // to do it here.
+        //
         if(NULL == (ent = autoent.Open(path, &meta, size, -1, O_RDWR, false, true, AutoLock::NONE))){
             S3FS_PRN_ERR("could not open file(%s): errno=%d", path, errno);
             return -EIO;
         }
-        if(0 != (result = ent->Load(0, size, AutoLock::NONE))){
-            S3FS_PRN_ERR("could not download file(%s): result=%d", path, result);
+        ent->UpdateCtime();
+
+#if defined(__APPLE__)
+        // [NOTE]
+        // Only for macos, this truncate calls to "size=0" do not reflect size.
+        // The cause is unknown now, but it can be avoided by flushing the file.
+        //
+        if(0 == size){
+            if(0 != (result = ent->Flush(autoent.GetPseudoFd(), true))){
+                S3FS_PRN_ERR("could not upload file(%s): result=%d", path, result);
                 return result;
             }
+            StatCache::getStatCacheData()->DelStat(path);
+        }
+#endif
 
-        ent->UpdateCtime();
     }else{
         // Not found -> Make tmpfile(with size)
-
         struct fuse_context* pcxt;
         if(NULL == (pcxt = fuse_get_context())){
             return -EIO;
@@ -2198,15 +2216,12 @@ static int s3fs_truncate(const char* _path, off_t size)
             S3FS_PRN_ERR("could not open file(%s): errno=%d", path, errno);
             return -EIO;
         }
-    }
-
-    // upload
         if(0 != (result = ent->Flush(autoent.GetPseudoFd(), true))){
             S3FS_PRN_ERR("could not upload file(%s): result=%d", path, result);
             return result;
         }
-
         StatCache::getStatCacheData()->DelStat(path);
+    }
     S3FS_MALLOCTRIM(0);
 
     return result;