iofunc_notify()

Install, poll, or remove a notification handler

Synopsis:

#include <sys/iofunc.h>

int iofunc_notify( resmgr_context_t *ctp,
                   io_notify_t *msg,
                   iofunc_notify_t *nop,
                   int trig,
                   const int *notifycounts,
                   int *armed );

Arguments:

ctp: A pointer to a resmgr_context_t structure that the resource-manager library uses to pass context information between functions.
msg: A pointer to the io_notify_t structure that contains the message that the resource manager received; see below.
nop: An array of three iofunc_notify_t structures that represent, in order, the input, output, and out-of-band notification lists; see below.
Generally, this structure is maintained by the resource manager within an extended attributes structure.
trig: A bitmask indicating which sources are currently satisfied, and could cause a trigger to occur. This bitmask is any combination of _NOTIFY_COND_INPUT, _NOTIFY_COND_OUTPUT and _NOTIFY_COND_OBAND.
You typically set this value, based on the conditions in effect at the time of the call.
notifycounts: NULL, or an array of three integers representing, in order, the number of elements that must be present in the input, output, and out-of-band queues in order for the event to be triggered. Note that if any condition is met, nothing is armed. Only if none of the conditions are met, does the event get armed in accordance with the notifycounts parameter. If this parameter is NULL, a value of 1 is assumed for all counts.
armed: NULL, or a pointer to a location where the function can store a 1 to indicate that a notification entry is armed, or a 0 otherwise.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The POSIX layer helper function iofunc_notify() is used by a resource manager to implement notification.

This routine examines the message that the resource manager received (passed in the msg argument), and determines what action the client code is attempting to perform:

_NOTIFY_ACTION_EDGEARM: Conditions are considered as met only if a change occurs since the last call to ionotify(..., _NOTIFY_ACTION_EDGEARM, ...). Met conditions are returned; a notification is armed for unmet conditions.
_NOTIFY_ACTION_CONDARM: If the conditions aren't met, arm the event and return EAGAIN; if the conditions are met, return a one-part IOV with the flags field set to indicate which conditions are available.
_NOTIFY_ACTION_POLL: Return a one-part IOV with the flags field set to indicate which conditions are available. The caller should return (_RESMGR_NPARTS(1)) to the resource manager library, which returns a one-part message to the client.
_NOTIFY_ACTION_POLLARM: Similar to _NOTIFY_ACTION_POLL, with the additional characteristic of arming the event if none of the conditions is met.
_NOTIFY_ACTION_TRANARM: For each of the sources specified, create a notification entry and store the client's struct sigevent event structure in it. Note that only one transition arm is allowed at a time per device. If the client specifies an event of SIGEV_NONE, the action is to disarm. When the event is triggered, the notification is automatically disarmed.

io_notify_t structure

The io_notify_t structure holds the _IO_NOTIFY or _IO_NOTIFY64 message received by the resource manager:

struct _io_notify {
    uint16_t                    type;
    uint16_t                    combine_len;
    int32_t                     action;
    int32_t                     flags;
    struct __sigevent32         event;

    /* Following fields only valid if (flags & _NOTIFY_COND_EXTEN) */
    int32_t                     mgr[2];    /* For use by manager */
    int32_t                     flags_extra_mask;
    int32_t                     flags_exten;
    int32_t                     nfds;
    int32_t                     fd_first;
    int32_t                     nfds_ready;
    int64_t                     timo;
    /* struct pollfd            fds[nfds]; */
};

struct _io_notify64 {
    uint16_t                    type;
    uint16_t                    combine_len;
    int32_t                     action;
    int32_t                     flags;
    struct __sigevent32         old_event;

    /* Following fields only valid if (flags & _NOTIFY_COND_EXTEN) */
    int32_t                     mgr[2];    /* For use by manager */
    int32_t                     flags_extra_mask;
    int32_t                     flags_exten;
    int32_t                     nfds;
    int32_t                     fd_first;
    int32_t                     nfds_ready;
    int64_t                     timo;
    union {
        struct __sigevent32     event32;
        struct __sigevent64     event64;
    };
    /* struct pollfd            fds[nfds]; */
};

struct _io_notify_reply {
    uint32_t                    zero;
    uint32_t                    flags;   /* actions above */
    int32_t                     flags2;  /* flags above */
    struct __sigevent32         event;

    /* Following fields only updated by new managers (if valid) */
    int32_t                     mgr[2];    /* For use by manager */
    int32_t                     flags_extra_mask;
    int32_t                     flags_exten;
    int32_t                     nfds;
    int32_t                     fd_first;
    int32_t                     nfds_ready;
    int64_t                     timo;
    /* struct pollfd            fds[nfds]; */
};

struct _io_notify_reply64 {
    uint32_t                    zero;
    uint32_t                    flags;  /* actions */
    int32_t                     flags2; /* flags above */
    struct __sigevent32         old_event;

    /* Following fields only updated by new managers (if valid) */
    int32_t                     mgr[2];    /* For use by manager */
    int32_t                     flags_extra_mask;
    int32_t                     flags_exten;
    int32_t                     nfds;
    int32_t                     fd_first;
    int32_t                     nfds_ready;
    int64_t                     timo;
    union {
        struct __sigevent32     event32;
        struct __sigevent64     event64;
    };
    /* struct pollfd            fds[nfds]; */
};

typedef union {
    struct _io_notify           i;
    struct _io_notify64         i64;
    struct _io_notify_reply     o;
    struct _io_notify_reply64   o64;
} io_notify_t;

The I/O message structures are unions of an input message (coming to the resource manager) and an output or reply message (going back to the client).

The i member (of type _io_notify) and the i64 member (of type _io_notify64) contain the following members:

type

_IO_NOTIFY or _IO_NOTIFY64.

combine_len

If the message is a combine message, _IO_COMBINE_FLAG is set in this member. For more information, see Combine Messages chapter of Writing a Resource Manager.

action

_NOTIFY_ACTION_CONDARM, _NOTIFY_ACTION_EDGEARM, _NOTIFY_ACTION_POLL, _NOTIFY_ACTION_POLLARM, or _NOTIFY_ACTION_TRANARM, as described above.

flags

One of the following:

_NOTIFY_COND_INPUT — this condition is met when there are one or more units of input data available (i.e., clients can now issue reads).
_NOTIFY_COND_OUTPUT — this condition is met when there's room in the output buffer for one or more units of data (i.e. clients can now issue writes).
_NOTIFY_COND_OBAND — the condition is met when one or more units of out-of-band data are available.
_NOTIFY_COND_EXTEN — the conditions are defined with the extended flags in the flags_exten member; used internally.

mgr[2]

For use by the manager.

flags_extra_mask

A mask for removing the extra flags from the flags member.

flags_exten

A bitset of the extended _NOTIFY_CONDE_* flags; used internally.

nfds

The number of entries in the array of pollfd structures that follows the message.

fd_first

The index of the first entry in the array of pollfd structures that has a non-negative file descriptor.

nfds_ready

The number of file descriptors that are ready.

timo

The time-out, in nanoseconds.

event32 or event64

A pointer to a sigevent structure that defines the event that the resource manager is to deliver once a condition is met.

As indicated by the comment, if _NOTIFY_COND_EXTEN is set in the flags, the message is followed by an array of pollfd structures. For more information about this structure, see poll().

The o member (of type _io_notify_reply) and the o64 member (of type _io_notify_reply64) contain the following members:

flags: Which of the conditions were triggered; see the flags for _io_notify, above.

It also includes updated copies of the extended fields.

iofunc_notify_t structure

The iofunc_notify_t structure is defined in <sys/iofunc.h> as follows:

typedef struct _iofunc_notify {
    int                         cnt;
    struct _iofunc_notify_event *list;
} iofunc_notify_t;

The members of the iofunc_notify_t structure include:

cnt: The smallest cnt member in the list; see below.
list: A pointer to a linked list of iofunc_notify_event_t structures that represent one of the input, output, and out-of-band notification lists.

CAUTION:

To avoid race conditions in multi-threaded server processes, you must serialize access to each iofunc_notify_t structure. For more information, see the note about locking iofunc_notify_t structures in “Handling ionotify(), poll(), and select()” in Writing a Resource Manager.

The iofunc_notify_event_t structure is defined as:

typedef struct _iofunc_notify_event {
    struct _iofunc_notify_event *next;
    int                         rcvid;
    int                         scoid;
    int                         cnt;
    struct __sigevent32         old_event;
    unsigned                    flags;
    int                         coid;
    union {
       struct sigevent          event;
       struct __sigevent32      event32;
       struct __sigevent64      event64;
    };
} iofunc_notify_event_t;

The members of the iofunc_notify_event_t structure include:

next

A pointer to the next element in the list.

rcvid

The receive ID of the client to notify.

scoid

The server connection ID.

cnt

The number of bytes available. Some clients, such as io-char, may want a sufficiently large amount of data to be available before they access it.

old_event

Maintained for backwards compatibility.

flags

A bitwise OR of zero or more of the following:

_NOTIFY_COND_EXTEN, plus any extended (_NOTIFY_CONDE_*) bits; used internally
_NOTIFY_EDGEEVENT — an edge condition is being masked for _NOTIFY_ACTION_EDGEARM

coid

The connection ID.

event

A pointer to a sigevent structure that defines the event that the resource manager is to deliver once a condition is met.

The sys/iofunc.h file also defines the following macros that work with the arrays of iofunc_notify_t structures:

#define IOFUNC_NOTIFY_DISARM(__nop, __index) ...: Disarm the list specified by __index in __nop.
#define IOFUNC_NOTIFY_INIT(__nop) ...: Initialize the three lists in __nop.

Returns:

-1: Success; the resource manager library should return a one-part IOV to the client.
EAGAIN: The action was _NOTIFY_ACTION_CONDARM, and the conditions weren't met.
EBUSY: A notification was already armed for this resource, and this library function enforces a restriction of one per resource.
EINVAL: Invalid action.
ENOMEM: There wasn't enough memory available to create an iofunc_notify_event_t structure.

Examples:

See Writing a Resource Manager.

Classification:

QNX Neutrino

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes