Provided by: libkeyutils-dev_1.6.3-6ubuntu2_amd64 
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 key_id indicates the key that was revoked and aux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.
SEE ALSO
keyctl(1), add_key(2), keyctl(2), request_key(2), keyctl(3), keyrings(7), keyutils(7)
Linux 28 Aug 2019 KEYCTL_GRANT_PERMISSION(3)