VFS: add F_FLUSH_FS_CACHE fcntl

This fcntl requests all cached blocks associated with the minor device
number associated with the regular file are invalidated. If the file
is a block special, invalidate the blocks associated with that minor
device instead.

This is to be used for a test that tests unmapped file-mapped memory
ranges whose blocks are not in the cache and therefore must be fetched
from a FS.

Change-Id: Ide914b2e88413aa90bd731ae587ca06fa5f13ebc

servers/mfs/misc.c

@@ -39,7 +39,7 @@ int fs_flush()
  * to disk.
  */
   dev_t dev = fs_m_in.REQ_DEV;
-  if(dev == fs_dev) return(EBUSY);
+  if(dev == fs_dev && lmfs_bufs_in_use() > 0) return(EBUSY);
  
   lmfs_flushall();
   lmfs_invalidate(dev);

servers/vfs/misc.c

@@ -223,6 +223,24 @@ int do_fcntl(void)
 	fl = (O_NOSIGPIPE);
 	f->filp_flags = (f->filp_flags & ~fl) | (fcntl_argx & fl);
 	break;
+    case F_FLUSH_FS_CACHE:
+    {
+	struct vnode *vn = f->filp_vno;
+	mode_t mode = f->filp_vno->v_mode;
+	if (!super_user) {
+		r = EPERM;
+	} else if (S_ISBLK(mode)) {
+		/* Block device; flush corresponding device blocks. */
+		r = req_flush(vn->v_bfs_e, vn->v_sdev);
+	} else if (S_ISREG(mode) || S_ISDIR(mode)) {
+		/* Directory or regular file; flush hosting FS blocks. */
+		r = req_flush(vn->v_fs_e, vn->v_dev);
+	} else {
+		/* Remaining cases.. Meaning unclear. */
+		r = ENODEV;
+	}
+	break;
+    }
     default:
 	r = EINVAL;
   }

sys/sys/fcntl.h

@@ -326,6 +326,7 @@ __END_DECLS
 
 #if defined(__minix)
 #define F_FREESP       100
+#define F_FLUSH_FS_CACHE	101	/* invalidate cache on associated FS */
 #endif /* defined(__minix) */
 
 #endif /* !_SYS_FCNTL_H_ */