View source for Kernel: vnode Operations

Summary of known vfs operations and [[Kernel: vnode and vfs|vnode]] operations.

=== 1. VFS Operations (<code>vfsops_t</code>) ===
These are operations on the '''filesystem as a whole''':
{| class="wikitable"
!Operation
!Purpose / Semantics
!Typical FS Relevance
|-
|<code>mount</code>
|Mount the filesystem; initialize structures, link root vnode.
|All FS
|-
|<code>umount</code>
|Unmount; flush buffers, release resources.
|All FS
|-
|<code>sync</code>
|Flush all dirty buffers and VM pages to disk.
|Persistent FS (EFS, XFS)
|-
|<code>statvfs</code>
|Retrieve filesystem statistics (free space, block size).
|All FS
|-
|<code>vget</code>
|Retrieve vnode by inode number or identifier.
|Persistent FS
|-
|<code>quotactl</code>
|Manage quotas on filesystem (user/group limits).
|Optional, persistent FS
|-
|<code>import</code>
|Integrate remote filesystem structures (NFS, exported FS).
|Network FS
|-
|<code>root</code>
|Return root vnode of filesystem.
|All FS
|-
|<code>reclaim</code>
|Cleanup filesystem-specific vnode data before freeing vnode memory.
|All FS
|-
|<code>fsid</code>
|Return filesystem ID.
|Persistent FS
|-
|<code>check</code>
|Perform consistency or integrity checks (optional).
|Persistent FS
|-
|<code>remount</code>
|Update mount options without unmounting.
|Optional
|-
|<code>statfs</code>
|Return summarized filesystem status.
|Persistent FS
|}
'''Notes:'''

* Pseudo-filesystems (pipefs, fifofs) stub most of these functions; only <code>root</code> or <code>vget</code> may return in-memory structures.
* Real filesystems (EFS, XFS) implement almost all operations for proper filesystem management.

----

=== 2. Vnode Operations (<code>vnodeops_t</code>) ===
These are operations on '''individual vnodes''', dispatched via the BHV layer.
{| class="wikitable"
!Operation
!Purpose / Semantics
!FS Relevance / Typical Implementation
|-
|<code>read</code>
|Read data from vnode into user or kernel buffer.
|All FS supporting files or streams
|-
|<code>write</code>
|Write data to vnode from buffer.
|All FS supporting files or streams
|-
|<code>ioctl</code>
|Perform device-specific or FS-specific commands.
|Devices, pseudo-FS, streams
|-
|<code>getattr</code>
|Retrieve vnode attributes (mode, owner, size, timestamps).
|All FS
|-
|<code>setattr</code>
|Update vnode attributes.
|All FS
|-
|<code>access</code>
|Check access permissions.
|All FS
|-
|<code>lookup</code>
|Resolve pathname component to vnode.
|Directory FS (EFS, XFS, pipefs limited)
|-
|<code>create</code>
|Create a new file.
|Persistent FS; pseudo-FS may stub
|-
|<code>remove</code>
|Remove a file.
|Persistent FS; pipefs/FIFO may implement
|-
|<code>mkdir</code>
|Create directory.
|Persistent FS
|-
|<code>rmdir</code>
|Remove directory.
|Persistent FS
|-
|<code>readdir</code>
|Read directory entries.
|Persistent FS
|-
|<code>symlink</code>
|Create symbolic link.
|Optional, persistent FS
|-
|<code>readlink</code>
|Read symbolic link target.
|Optional, persistent FS
|-
|<code>rename</code>
|Rename a file.
|Persistent FS
|-
|<code>link</code>
|Create hard link.
|Persistent FS
|-
|<code>unlink</code>
|Remove a link.
|Persistent FS
|-
|<code>fsync</code>
|Flush vnode’s buffers to disk.
|Persistent FS
|-
|<code>map</code>
|Map file pages into VM.
|Persistent FS, memory-mapped files
|-
|<code>addmap</code>
|Notify FS of memory mapping.
|Persistent FS
|-
|<code>delmap</code>
|Notify FS of unmapped region.
|Persistent FS
|-
|<code>frlock</code>
|File region locking.
|All FS supporting advisory locks
|-
|<code>poll</code>
|Determine readiness for I/O.
|Streams, pipes, devices
|-
|<code>seek</code>
|Validate seek operation.
|Regular files, optionally pseudo-FS
|-
|<code>inactive</code>
|Called when last reference released; free resources.
|All FS
|-
|<code>reclaim</code>
|Called to cleanup filesystem-specific vnode state.
|All FS
|-
|<code>realvp</code>
|Return underlying “real” vnode in layered FS.
|Stacked or layered FS
|-
|<code>cover</code>
|Return vnode that this vnode overlays.
|Stacked FS
|-
|<code>link_removed</code>
|Notify FS that a link was removed.
|Persistent FS
|}
'''Notes:'''

* '''Pseudo-filesystems''' (pipefs, fifofs):
** Implement <code>read</code>, <code>write</code>, <code>poll</code>, <code>inactive</code>
** Many other operations are stubs (<code>fs_nosys</code>) because they have no persistent storage.
* '''Persistent filesystems''' (EFS, XFS):
** Implement almost all operations fully.
** VM integration (<code>map</code>, <code>addmap</code>, <code>delmap</code>) links vnode buffers with page cache.
** Locking (<code>frlock</code>) and attribute operations are critical for filesystem consistency.
* '''Streams / devices:'''
** Integrate with <code>poll</code> / <code>select</code> via pollhead structures.
** <code>ioctl</code> is heavily used to expose device-specific functionality.

----

=== 3. Behavior Semantics ===

* Vnode operations are '''dispatched via the behavior chain''', allowing:
** '''Layered filesystems''': stacking additional behaviors (e.g., shadow vnodes, network FS).
** '''Pseudo-filesystems''': handle vnodes without disk backing.
* Operations are '''always invoked on BHV descriptors''', not directly on vnodes. This ensures correct dispatch in multi-layer environments.

----

=== 4. Filesystem Type Considerations ===
{| class="wikitable"
!FS Type
!Implemented Operations
|-
|Persistent (EFS/XFS)
|All VFS and vnode ops; full VM/page cache integration, locking, attributes
|-
|Pseudo-FS (pipefs/fifofs)
|<code>read</code>, <code>write</code>, <code>poll</code>, <code>inactive</code>; stubs for most others
|-
|Device FS (devfs)
|<code>read</code>, <code>write</code>, <code>ioctl</code>, <code>poll</code>, <code>getattr</code>/<code>setattr</code>
|-
|Network FS (NFS-like)
|<code>import</code>, <code>vget</code>, <code>root</code>, <code>lookup</code>, <code>read</code>, <code>write</code>
|}
----

=== 5. Reference / Lifecycle Management ===

* '''VFS ops:''' <code>reclaim</code> and <code>sync</code> ensure global cleanup.
* '''Vnode ops:''' <code>inactive</code> and <code>reclaim</code> ensure per-vnode cleanup.
* '''BHVs:''' behavior chain allows multiple layers to participate in cleanup or dispatch.