CALLBACK(9) BSD Kernel Developer's Manual CALLBACK(9)NAMEcallback — generic callback interface
SYNOPSIS
#include <sys/callback.h>
void
callback_head_init(struct callback_head *ch, int ipl);
void
callback_head_destroy(struct callback_head *ch);
void
callback_register(struct callback_head *ch, struct callback_entry *ce,
void *obj, int (*fn)(struct callback_entry *, void *, void *));
void
callback_unregister(struct callback_head *ch, struct callback_entry *ce);
int
callback_run_roundrobin(struct callback_head *ch, void *arg);
DESCRIPTION
The generic callback interface allows lower-level layer code to execute a
registered function, or set of functions, from the higher-level layer.
Registered functions must return one of these constants:
CALLBACK_CHAIN_CONTINUE
Indicates that the function call was successful. The fol‐
lowing functions in the chain will be called.
CALLBACK_CHAIN_ABORT
Indicates a failure case in the function call. Any follow‐
ing functions in the chain will not be executed.
FUNCTIONS
The callback structure callback_head should be initialized and destroyed
using the functions described below. This structure contains the list of
callback entries and other internal data.
The callback_entry structure is an entry, normally associated with the
higher-level object. It contains the internal data of the callback
interface.
callback_head_init(ch, ipl)
Initialize the callback structure specified by ch. The highest
IPL at which this callback can be used is specified by ipl.
callback_head_destroy(ch)
Destroy the callback structure specified by ch. The caller must
unregister all functions before destroying the callback struc‐
ture.
callback_register(ch, ce, obj, fn)
Register the callback function in the callback structure speci‐
fied by ch. ce should point to the entry structure of the call‐
back object. The callback object itself is specified by obj.
The function pointer is specified by fn.
callback_unregister(ch, ce)
Unregister the callback function from the structure specified by
ch. The entry should be passed as ce. This function may block.
callback_run_roundrobin(ch, arg)
Executes all functions registered in the callback structure,
specified by ch. The functions are executed in round-robin
fashion. The value of arg will be passed to the callback func‐
tions.
CODE REFERENCES
The callback interface is implemented within the file
sys/kern/subr_callback.c.
SEE ALSOintro(9)BSD October 28, 2009 BSD