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.Dd October 28, 2009 .Dt CALLBACK 9 .Os .Sh NAME .Nm callback .Nd generic callback interface .Sh SYNOPSIS n sys/callback.h .Ft void .Fn callback_head_init "struct callback_head *ch" "int ipl" .Ft void .Fn callback_head_destroy "struct callback_head *ch" .Ft void .Fn callback_register \ "struct callback_head *ch" "struct callback_entry *ce" "void *obj" \ "int (*fn)(struct callback_entry *, void *, void *)" .Ft void .Fn callback_unregister "struct callback_head *ch" "struct callback_entry *ce" .Ft int .Fn callback_run_roundrobin "struct callback_head *ch" "void *arg" .Sh DESCRIPTION The generic .Nm callback interface allows lower-level layer code to execute a registered function, or set of functions, from the higher-level layer.
p Registered functions must return one of these constants: l -tag -width Dv t Dv CALLBACK_CHAIN_CONTINUE Indicates that the function call was successful. The following functions in the chain will be called. t Dv CALLBACK_CHAIN_ABORT Indicates a failure case in the function call. Any following functions in the chain will not be executed. .El .Sh FUNCTIONS The callback structure .Vt callback_head should be initialized and destroyed using the functions described below. This structure contains the list of callback entries and other internal data.
p The .Vt callback_entry structure is an entry, normally associated with the higher-level object. It contains the internal data of the callback interface. l -tag -width compact t Fn callback_head_init "ch" "ipl" Initialize the callback structure specified by .Fa ch . The highest IPL at which this callback can be used is specified by .Fa ipl . t Fn callback_head_destroy "ch" Destroy the callback structure specified by .Fa ch . The caller must unregister all functions before destroying the callback structure. t Fn callback_register "ch" "ce" "obj" "fn" Register the callback function in the callback structure specified by .Fa ch . .Fa ce should point to the entry structure of the callback object. The callback object itself is specified by .Fa obj . The function pointer is specified by .Fa fn . t Fn callback_unregister "ch" "ce" Unregister the callback function from the structure specified by .Fa ch . The entry should be passed as .Fa ce . This function may block. t Fn callback_run_roundrobin "ch" "arg" Executes all functions registered in the callback structure, specified by .Fa ch . The functions are executed in round-robin fashion. The value of .Fa arg will be passed to the callback functions. .El .Sh CODE REFERENCES The .Nm interface is implemented within the file
a sys/kern/subr_callback.c . .Sh SEE ALSO .Xr intro 9
Indexes created Sat Sep 20 22:09:52 GMT 2025