Table of Contents
The PFS-VFS protocol
This page provides the official documentation of the PFS-VFS protocol of MINIX 3. It describes the protocol used between the PFS server and the VFS server. The current version documents the protocol used in SVN revision 9568. If you update this document because of changes to MINIX 3, please mention the revision number of the change in the wiki comment.
General Overview
In order to implement file descriptor passing and better socket file permission checking, PFS has to make a few nested VFS calls. The requests are outlined below.
Access Control Messages
PFS_REQ_CHECK_PERMS
Check Permissions.
Request fields
| <16% >USER_ENDPT | m2_i2 | endpoint_t | The endpoint of the process that wishes to bind()/connect(). |
| IO_GRANT | m2_p1 | cp_grant_id_t | Path to the socket file. |
| COUNT | m2_i3 | int | Length of the path. |
Reply fields
- none
Reply codes
| <16% >OK | Permissions verified to be okay. |
| EACCES | Access Denied. |
| EINVAL | Invalid endpoint or strlen. |
| EIO | Couldn't copy path from grant. |
| ELOOP | More than SYMLOOP_MAX levels of symlinks were encountered when resolving the path. |
| ENOENT | File not found. |
| ENAMETOOLONG | The resolved path is too big to fit into the space provided in the grant. |
Description
This request asks the VFS to resolve the given path and determine if the user has permission to access it.
File Descriptor Passing Messages
PFS_REQ_VERIFY_FD
Verify a file descriptor.
Request fields
| <16% >USER_ENDPT | m2_i2 | endpoint_t | The endpoint of the process that owns the descriptor to be verified. |
| COUNT | m2_i3 | int | File descriptor number. |
Reply fields
| <16% >ADDRESS | m2_p1 | filp_id_t | The filp that corresponds to the file descriptor. |
Reply codes
| <16% >OK | The file descriptor is valid. |
| EINVAL | The file descriptor is not valid. |
Description
Verify whether the given file descriptor is valid for the endpoint. When the file descriptor is valid a pointer to that filp is returned.
PFS_REQ_SET_FILP
Mark a filp as in-flight.
Request fields
| <16% >ADDRESS | m2_p1 | filp_id_t | The filp that corresponds to the file descriptor. |
Reply fields
- none
Reply codes
| <16% >OK | The filp was marked as in-flight. |
| EINVAL | The filp is invalid. |
Description
This sets a flag on the filp that prevents it from being closed while it is being copied to another process.
PFS_REQ_COPY_FILP
Copy a filp.
Request fields
| <16% >USER_ENDPT | m2_i2 | endpoint_t | The destination. |
| ADDRESS | m2_p1 | filp_id_t | The filp to be copied. |
Reply fields
- none
Reply codes
| <16% >int >= 0 | The new file descriptor number. |
| EINVAL | The endpoint and/or filp parameters are invalid. |
| EMFILE | The file descriptor table of the destination endpoint is full. |
Description
This copies a filp from one process to another.
PFS_REQ_PUT_FILP
Mark a filp as not in-flight.
Request fields
| <16% >ADDRESS | m2_p1 | filp_id_t | The filp that corresponds to the file descriptor. |
Reply fields
- none
Reply codes
| <16% >OK | The filp was marked as not in-flight. |
| EINVAL | The filp is invalid. |
Description
This unsets a flag on the filp that prevents it from being closed while it is being copied to another process.
PFS_REQ_CANCEL_FD
Cancel a file descriptor copy.
Request fields
| <16% >USER_ENDPT | m2_i2 | endpoint_t | The endpoint of the process that owns the descriptor to be verified. |
| COUNT | m2_i3 | int | File descriptor number. |
Reply fields
- none
Reply codes
| <16% >OK | The copy was cancelled. | |
| EINVAL | The file descriptor and/or endpoint parameters are invalid. | |
Description
This reverses the changes made by PFS_REQ_COPY_FILP.
