Manpages - keyctl_watch_key.3

NAME
SYNOPSIS
DESCRIPTION
- Notification Record
- Removal Notification
RETURN VALUE
ERRORS
LINKING
SEE ALSO

NAME

keyctl_watch_key - Watch for changes to a key

SYNOPSIS

  #include <keyutils.h>

  long keyctl_watch_key(key_serial_t key,
   int watch_queue_fd
   int watch_id);

DESCRIPTION

*keyctl_watch_key*() sets or removes a watch on key.

watch_id specifies the ID for a watch that will be included in notification messages. It can be between 0 and 255 to add a key; it should be -1 to remove a key.

watch_queue_fd is a file descriptor attached to a watch_queue device instance. Multiple openings of a device provide separate instances. Each device instance can only have one watch on any particular key.

Notification Record

Key-specific notification messages that the kernel emits into the buffer have the following format:

  struct key_notification {
  	struct watch_notification watch;
  	__u32	key_id;
  	__u32	aux;
  };

The watch.type field will be set to WATCH_TYPE_KEY_NOTIFY and the watch.subtype field will contain one of the following constants, indicating the event that occurred and the watch_id passed to keyctl_watch_key() will be placed in watch.info in the ID field. The following events are defined:

NOTIFY_KEY_INSTANTIATED: This indicates that a watched key got instantiated or negatively instantiated. key_id indicates the key that was instantiated and aux is unused.
NOTIFY_KEY_UPDATED: This indicates that a watched key got updated or instantiated by update. key_id indicates the key that was updated and aux is unused.
NOTIFY_KEY_LINKED: This indicates that a key got linked into a watched keyring. key_id indicates the keyring that was modified aux indicates the key that was added.
NOTIFY_KEY_UNLINKED: This indicates that a key got unlinked from a watched keyring. key_id indicates the keyring that was modified aux indicates the key that was removed.
NOTIFY_KEY_CLEARED: This indicates that a watched keyring got cleared. key_id indicates the keyring that was cleared and aux is unused.
NOTIFY_KEY_REVOKED: This indicates that a watched key got revoked. key_id indicates the key that was revoked and aux is unused.
NOTIFY_KEY_INVALIDATED: This indicates that a watched key got invalidated. key_id indicates the key that was invalidated and aux is unused.
NOTIFY_KEY_SETATTR: This indicates that a watched key had its attributes (owner, group, permissions, timeout) modified. key_id indicates the key that was modified and aux is unused.

Removal Notification

When a watched key is garbage collected, all of its watches are automatically destroyed and a notification is delivered to each watcher. This will normally be an extended notification of the form:

  struct watch_notification_removal {
  	struct watch_notification watch;
  	__u64	id;
  };

The watch.type field will be set to WATCH_TYPE_META and the watch.subtype field will contain WATCH_META_REMOVAL_NOTIFICATION. If the extended notification is given, then the length will be 2 units, otherwise it will be 1 and only the header will be present.

The watch_id passed to keyctl_watch_key/() will be placed in /watch.info in the ID field.

If the extension is present, id will be set to the ID of the destroyed key.

RETURN VALUE

On success keyctl_watch_key*() returns *0 . On error, the value -1 will be returned and errno will have been set to an appropriate error.

ERRORS

ENOKEY: The specified key does not exist.
EKEYEXPIRED: The specified key has expired.
EKEYREVOKED: The specified key has been revoked.
EACCES: The named key exists, but does not grant view permission to the calling process.
EBUSY: The specified key already has a watch on it for that device instance (add only).
EBADSLT: The specified key doesn’t have a watch on it (removal only).

LINKING

This is a library function that can be found in libkeyutils. When linking, -lkeyutils should be specified to the linker.