PFS Open Context and the Open

An 8-byte Open_token can be returned by the PFS from vn_open and the LFS will pass this token back to the PFS on the following vnode operations when they are invoked from within this open context:

Vn_rdwr       vn_setattr  vn_fsync
Vn_readdir    vn_getattr  vn_lockctl
Vn_readwritev vn_trunc    vn_close

The token is passed in the OSI structure in the field osi_opentoken. To activate this support, the PFS sets the pfsi_opentokens flag as part of its output from PFS initialization.

Note that there will not always be an Open Token passed on all of these vnode operations. For example, there are both pathname and file descriptor forms of syscalls that generate vn_getatttr or vn_setattr, such as stat()/fstat() and chmod()/fchmod(). Pathname operations are not within an open context. The read/write operations can be invoked by programs using the VFS Server v_op interface. These are not part of an open context. An Open Token is always passed on vn_close and vn_trunc if one was returned on the corresponding vn_open.

Attention: If a file system has a PFS that uses Open_tokens, then that file system cannot be remounted.