fileincref -> filedup (consistent with idup)

defs.h

@@ -28,7 +28,7 @@ int             exec(char*, char**);
 // file.c
 struct file*    filealloc(void);
 void            fileclose(struct file*);
-void            fileincref(struct file*);
+struct file*    filedup(struct file*);
 void            fileinit(void);
 int             fileread(struct file*, char*, int n);
 int             filestat(struct file*, struct stat*);

file.c

@@ -41,14 +41,15 @@ filealloc(void)
 }
 
 // Increment ref count for file f.
-void
-fileincref(struct file *f)
+struct file*
+filedup(struct file *f)
 {
   acquire(&file_table_lock);
   if(f->ref < 1 || f->type == FD_CLOSED)
-    panic("fileincref");
+    panic("filedup");
   f->ref++;
   release(&file_table_lock);
+  return f;
 }
 
 // Read from file f.  Addr is kernel address.

proc.c

@@ -129,10 +129,9 @@ copyproc(struct proc *p)
     }
     memmove(np->mem, p->mem, np->sz);
 
-    for(i = 0; i < NOFILE; i++){
-      if((np->ofile[i] = p->ofile[i]) != 0)
-        fileincref(np->ofile[i]);
-    }
+    for(i = 0; i < NOFILE; i++)
+      if(p->ofile[i])
+        np->ofile[i] = filedup(p->ofile[i]);
     np->cwd = idup(p->cwd);
   }
 

sysfile.c

@@ -83,7 +83,7 @@ sys_dup(void)
     return -1;
   if((fd=fdalloc(f)) < 0)
     return -1;
-  fileincref(f);
+  filedup(f);
   return fd;
 }