fix: improve mount quota enforcement to prevent overflow (#7804)

* fix: improve mount quota enforcement to prevent overflow (fixes seaweedfs-csi-driver#218)

* test: add unit tests for quota enforcement

weed/mount/weedfs_file_write.go

@@ -36,7 +36,8 @@ import (
  */
 func (wfs *WFS) Write(cancel <-chan struct{}, in *fuse.WriteIn, data []byte) (written uint32, code fuse.Status) {
 
-	if wfs.IsOverQuota {
+	// Check quota including uncommitted writes for real-time enforcement
+	if wfs.IsOverQuotaWithUncommitted() {
 		return 0, fuse.Status(syscall.ENOSPC)
 	}
 
@@ -59,7 +60,16 @@ func (wfs *WFS) Write(cancel <-chan struct{}, in *fuse.WriteIn, data []byte) (wr
 
 	entry.Content = nil
 	offset := int64(in.Offset)
-	entry.Attributes.FileSize = uint64(max(offset+int64(len(data)), int64(entry.Attributes.FileSize)))
+	oldFileSize := int64(entry.Attributes.FileSize)
+	newFileSize := max(offset+int64(len(data)), oldFileSize)
+	entry.Attributes.FileSize = uint64(newFileSize)
+
+	// Track uncommitted bytes for real-time quota enforcement.
+	// Only count the new bytes being added beyond the current file size.
+	if newFileSize > oldFileSize {
+		wfs.AddUncommittedBytes(newFileSize - oldFileSize)
+	}
+
 	// glog.V(4).Infof("%v write [%d,%d) %d", fh.f.fullpath(), req.Offset, req.Offset+int64(len(req.Data)), len(req.Data))
 
 	fh.dirtyPages.AddPage(offset, data, fh.dirtyPages.writerPattern.IsSequentialMode(), tsNs)