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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022

port_dissociate (3C)


port_associate, port_dissociate - associate or dissociate the object with the port


#include <port.h>

int port_associate(int port, int source, uintptr_t object,
     int events, void *
int port_dissociate(int port, int source, uintptr_t object);


The port_associate() function associates specific events of a given object with a port. Only objects associated with a particular port are able to generate events that can be retrieved using port_get(3C) or port_getn(3C). The delivery event has its portev_user member set to the value specified in the user parameter. If the specified object is already associated with the specified port, the port_associate() function serves to update the events and user arguments of the association. The port_dissociate() function removes the association of an object with a port.

The objects that can be associated with a port by way of the port_associate() function are objects of type PORT_SOURCE_FD and PORT_SOURCE_FILE. Objects of other types have type-specific association mechanisms. A port_notify_t structure, defined in <port.h>, is used to specify the event port and an application-defined cookie to associate with these event sources. See port_create(3C) and signal.h(3HEAD).

The port_notify_t structure contains the following members:

int       portntfy_port;  /* bind request(s) to port */
void      *portntfy_user; /* user defined cookie */

Objects of type PORT_SOURCE_FD are file descriptors. The event types for PORT_SOURCE_FD objects are described in poll(2). At most one event notification will be generated per associated file descriptor. For example, if a file descriptor is associated with a port for the POLLRDNORM event and data is available on the file descriptor at the time the port_associate () function is called, an event is immediately sent to the port. If data is not yet available, one event is sent to the port when data first becomes available.

When an event for a PORT_SOURCE_FD object is retrieved, the object no longer has an association with the port. The event can be processed without the possibility that another thread can retrieve a subsequent event for the same object. After processing of the file descriptor is completed, the port_associate() function can be called to reassociate the object with the port.

Objects of type PORT_SOURCE_FILE are pointer to the structure file_obj defined in <sys/port.h>. This event source provides event notification when the specified file/directory is accessed or modified or when its status changes. The path name of the file/directory to be watched is passed in the struct file_obj along with the access, modification, and change time stamps acquired from a stat(2) call. If the file name is a symbolic link, it is followed by default. The FILE_NOFOLLOW needs to be passed in along with the specified events if the symbolic link itself needs to be watched and lstat() needs to be used to get the file status of the symbolic link file.

The struct file_obj contains the following elements:

timestruc_t     fo_atime;  /* Access time from stat() */
timestruc_t     fo_mtime;  /* Modification time from stat() */
timestruc_t     fo_ctime;  /* Change time from stat() */
char            *fo_name;  /* Pointer to a null terminated path name */

At the time the port_associate() function is called, the timestamps passed in the structure file_obj are compared with the file or directory's current time stamps and, if there has been a change, an event is immediately sent to the port. If not, an event will be sent when such a change occurs. If all the time stamps passed in file_obj structure are set to zero, this routine behaves as if the timestamps were set to the values obtained from a call to the stat() function at the moment of the call to the port_associate() function.

The event types that can be specified at port_associate() time for PORT_SOURCE_FILE are FILE_ACCESS, FILE_MODIFIED, and FILE_ATTRIB, corresponding to the three time stamps. An fo_atime change results in the FILE_ACCESS event, an fo_mtime change results in the FILE_MODIFIED event, and an fo_ctime change results in the FILE_ATTRIB event.

The following exception events are delivered when they occur. These event types cannot be filtered.

FILE_DELETE       /* Monitored file/directory was deleted */
FILE_RENAME_TO    /* Monitored file/directory was renamed */
FILE_RENAME_FROM  /* Monitored file/directory was renamed */
UNMOUNTED         /* Monitored file system got unmounted */
MOUNTEDOVER       /* Monitored file/directory was mounted over */

At most one event notification will be generated per associated file_obj. When the event for the associated file_obj is retrieved, the object is no longer associated with the port. The event can be processed without the possibility that another thread can retrieve a subsequent event for the same object. The port_associate() can be called to reassociate the file_obj object with the port.

The association is also removed if the port gets closed or when port_dissociate() is called.

The parent and child processes are allowed to retrieve events from file descriptors shared after a call to fork(2). The process performing the first association with a port (parent or child process) is designated as the owner of the association. Only the owner of an association is allowed to dissociate the file descriptor from a port. The association is removed if the owner of the association closes the port.

On NFS file systems, events from only the client side (local) access/modifications to files or directories will be delivered.

Objects of event source type PORT_SOURCE_POSTWAIT are a pointer to the struct postwk_obj_t defined in <sys/port.h>. This event source provides post events submitted by postwait_post(3C), postwait_postn(3C), and postwait_post_deferred(3C). The struct postwk_obj_t contains the following elements:

int          ko_flags     /* flags */
postwkey_t   ko_key;      /* key from postwait_genkey(3C) call */

The key is acquired by calling postwait_genkey(3C).

One event at a time is delivered for an associated key with type POSTWKEY_COUNTING specified in ko_flags. Along with the event a count of number of times the key was posted since the last time an event was retrieved is returned in port_events member of the port_event_t struct.

If type POSTWKEY_QUEUING is specified in ko_flags, one event for every post submitted will be delivered. Each event has the portev_events and portev_user members of port_event_t set to the user event and user value passed with the submitted post respectively.

The postwk_obj_t object pointer is returned in the portev_object member.

For POSTWKEY_QUEUING key association type, the user cookie passed at the time of port_associate call is ignored by this event source.

If the OR operation is performed on POSTWKEY_EXCLUSIVE with either POSTWKEY_COUNTING or POSTWKEY_QUEUING, the calling process must be the first to associate this key. Association will fail if the specified key has already been associated with a port, regardless of whether or not POSTWKEY_EXCLUSIVE was specified.

Return Values

Upon successful completion, 0 is returned. Otherwise, −1 is returned and errno is set to indicate the error.


The port_associate() and port_dissociate () functions will fail if:


The port identifier is not valid.


The source argument is of type PORT_SOURCE_FD and the object argument is not a valid file descriptor.


The source argument is not valid.


If the source is PORT_SOURCE_POSTWAIT, the key specified is already associated with the port.


If the source is PORT_SOURCE_POSTWAIT, the postwk_obj_t pointer is invalid.


If the source is PORT_SOURCE_POSTWAIT and POSTWKEY_EXCLUSIVE was specified, another port is already associated with this key, or this key has been already associated with another port with POSTWKEY_EXCLUSIVE specified.


If the source is PORT_SOURCE_POSTWAIT, incorrect type specified in ko_flags.

The port_associate() function will fail if:


The source argument is PORT_SOURCE_FILE and, Search permission is denied on a component of path prefix or the file exists and the permissions, corresponding to the events argument, are denied.


The maximum number of objects associated with the port was exceeded. The maximum allowable number of events or association of objects per port is the minimum value of the process.max-port-events resource control at the time port_create(3C) was used to create the port. See setrctl(2) and rctladm(8) for information on using resource controls.

The number of objects associated with a port is composed of all supported resource types. Some of the source types do not explicitly use the port_associate() function.


The source argument is PORT_SOURCE_FILE and the file does not exist or the path prefix does not exist or the path points to an empty string. The source argument is PORT_SOURCE_SIGNAL and the object argument (signal) is one of the following SIGKILL, SIGSTOP, SIGILL, SIGSEGV, SIGFPE.


The physical memory limits of the system have been exceeded.


The source argument is PORT_SOURCE_FILE and the file system on which the specified file resides, does not support watching for file events notifications.

The port_dissociate() function will fail if:


The process is not the owner of the association.


The specified object is not associated with the port.


Example 1 Retrieve data from a pipe file descriptor.

The following example retrieves data from a pipe file descriptor.

#include <port.h>

int               port;
int               fd;
int               error;
int               index;
void              *mypointer;
port_event_t      pev;
struct timespec_t timeout;
char              rbuf[STRSIZE];
int               fds[MAXINDEX];

/* create a port */
port = port_create();

for (index = 0; index < MAXINDEX; index++) {
    error = mkfifo(name[index], S_IRWXU | S_IRWXG | S_IRWXO);
    if (error)
            /* handle error code */
    fds[index] = open(name[index], O_RDWR);

    /* associate pipe file descriptor with the port */
    error = port_associate(port, PORT_SOURCE_FD, fds[index],
        POLLIN, mypointer);
timeout.tv_sec = 1;     /* user defined */
timeout.tv_nsec = 0;

/* loop to retrieve data from the list of pipe file descriptors */
for (...) {
    /* retrieve a single event */
    error = port_get(port, &pev, &timeout);
    if (error) {
            /* handle error code */
    fd = pev.portev_object;
    if (read(fd, rbuf, STRSIZE)) {
            /* handle error code */
    if (fd-still-accepting-data) {
             * re-associate the file descriptor with the port.
             * The re-association is required for the
             * re-activation of the data detection.
             * Internals events and user arguments are set to the
             * new (or the same) values delivered here.
            error = port_associate(port, PORT_SOURCE_FD, fd, POLLIN,
    } else {
             * If file descriptor is no longer required,
             * - it can remain disabled but still associated with
             *   the port, or
             * - it can be dissociated from the port.
Example 2 Bind AIO transaction to a specific port.

The following example binds the AIO transaction to a specific port.

#include <port.h>

int             port;
port_notify_t   pn;
aiocb_t         aiocb;
aiocb_t         *aiocbp;
void            *mypointer;
int             error;
int             my_errno;
int             my_status;
struct timespec_t timeout;
port_event_t    pev;

port = port_create();
/* fill AIO specific part */
aiocb.aio_fildes = fd;
aiocb.aio_nbytes = BUFSIZE;
aiocb.aio_buf = bufp;
aiocb.aio_offset = 0;

/* port specific part */
pn.portnfy_port = port;
pn.portnfy_user = mypointer;
aiocb.aio_sigevent.sigev_notify = SIGEV_PORT;
aiocb.aio_sigevent.sigev_value.sival_ptr = &pn

 * The aio_read() function binds internally the asynchronous I/O
 * transaction with the port delivered in port_notify_t.
error = aio_read(&aiocb);

timeout.tv_sec = 1;     /* user defined */
timeout.tv_nsec = 0;

/* retrieve a single event */
error = port_get(port, &pev, &timeout);
if (error) {
        /* handle error code */

 * pev.portev_object contains a pointer to the aiocb structure
 * delivered in port_notify_t (see aio_read()).
aiocbp = pev.portev_object;

/* check error code and return value in
my_errno = aio_error(aiocbp);
my_status = aio_return(aiocbp);

Example 3 Using signals as an event source.

The following example shows a way to use signals as an event source.

#include <port.h>

int             portfd;
sigset_t        mask;
port_event_t    pe;
siginfo_t       si;
timespec_t      ts;

/* Create a port and associate PORT_SOURCE_SIGNAL with it */
portfd = port_create();
port_associate(portfd, PORT_SOURCE_SIGNAL, SIGUSR1, 0, (void *) &up);

/* Block the signals of interest */
(void)sigaddset(&mask, SIGUSR1);
sigprocmask(SIG_BLOCK, &mask, NULL);

kill(getpid(), SIGUSR1);

port_get(portfd, &pe, NULL);
ts.tv_sec = 0;
ts.tv_nsec = 0;
 * 'while' loop to consume all pending signals.
 * see sigtimedwait(3C).
while (sigtimedwait(&mask, &si, &ts) != -1) {
              /* fill code to consume signal here */

port_dissociate(portfd, PORT_SOURCE_SIGNAL, SIGUSR1)


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

poll(2), setrctl(2), port_alert(3C), port_create(3C), port_get(3C), port_send(3C), postwait_genkey(3C), postwait_post(3C), postwait_postn(3C), postwait_post_deferred(3C), signal.h(3HEAD), attributes(7), rctladm(8)