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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH POLL 4D "January 10, 2020" .SH NAME poll \- driver for fast poll on many file descriptors .SH SYNOPSIS .nf \fB#include int fd = open("/dev/poll", O_RDWR); ssize_t n = write(int fd, struct pollfd buf[], int bufsize); int n = ioctl(int fd, DP_POLL, struct dvpoll* arg); int n = ioctl(int fd, DP_ISPOLLED, struct pollfd* pfd);\fR .fi .SH PARAMETERS .ne 2 .na \fB\fIfd\fR \fR .ad .RS 12n Open file descriptor that refers to the \fB/dev/poll\fR driver. .RE .sp .ne 2 .na \fB\fIpath\fR \fR .ad .RS 12n \fB/dev/poll\fR .RE .sp .ne 2 .na \fB\fIbuf\fR \fR .ad .RS 12n Array of \fBpollfd\fR structures. .RE .sp .ne 2 .na \fB\fIbufsize\fR \fR .ad .RS 12n Size of \fIbuf\fR in bytes. .RE .sp .ne 2 .na \fB\fIarg\fR \fR .ad .RS 12n Pointer to \fBpollcall\fR structure. .RE .sp .ne 2 .na \fB\fIpfd\fR \fR .ad .RS 12n Pointer to \fBpollfd\fR structure. .RE .SH DESCRIPTION The \fB/dev/poll\fR driver is a special driver that enables you to monitor multiple sets of polled file descriptors. By using the \fB/dev/poll\fR driver, you can efficiently poll large numbers of file descriptors. Access to the \fB/dev/poll\fR driver is provided through \fBopen\fR(2), \fBwrite\fR(2), and \fBioctl(2)\fR system calls. .sp .LP Writing an array of \fBpollfd\fR struct to the \fB/dev/poll\fR driver has the effect of adding these file descriptors to the monitored \fBpoll\fR file descriptor set represented by the \fIfd\fR. To monitor multiple file descriptor sets, open the \fB/dev/poll\fR driver multiple times. Each \fBfd\fR corresponds to one set. For each \fBpollfd\fR struct entry (defined in \fBsys/poll.h\fR): .sp .in +2 .nf struct pollfd { int fd; short events; short revents; } .fi .in -2 .sp .LP The \fBfd\fR field specifies the file descriptor being polled. The \fBevents\fR field indicates the interested \fBpoll\fR \fBevents\fR on the file descriptor. If a \fBpollfd\fR array contains multiple \fBpollfd\fR entries with the same \fBfd\fR field, the "events" field in each \fBpollfd\fR entry is OR'ed. A special \fBPOLLREMOVE\fR event in the \fBevents\fR field of the \fBpollfd\fR structure removes the \fBfd\fR from the monitored set. The \fBrevents\fR field is not used. Write returns the number of bytes written successfully or \fB-1\fR when write fails. .sp .LP The \fBDP_POLL\fR ioctl is used to retrieve returned \fBpoll\fR \fBevents\fR occurred on the polled file descriptors in the monitored set represented by \fIfd\fR. \fIarg\fR \fIis\fR \fIa\fR pointer to the devpoll structures which are defined as follows: .sp .in +2 .nf struct dvpoll { struct pollfd* dp_fds; int dp_nfds; int dp_timeout; } .fi .in -2 .sp .LP The \fBdp_fds\fR points to a buffer that holds an array of returned \fBpollfd\fR structures. The \fBdp_nfds\fR field specifies the size of the buffer in terms of the number of \fBpollfd\fR entries it contains. The \fBdp_nfds\fR field also indicates the maximum number of file descriptors from which poll information can be obtained. If there is no interested \fBevents\fR on any of the polled file descriptors, the \fBDP_POLL\fR ioctl call will wait \fBdp_timeout\fR milliseconds before returning. If \fBdp_timeout\fR is \fB0\fR, the ioctl call returns immediately. If \fBdp_timeout\fR is \fB-1\fR, the call blocks until an interested \fBpoll\fR \fBevents\fR is available or the call is interrupted. Upon return, if the ioctl call has failed, \fB-1\fR is returned. The memory content pointed by \fBdp_fds\fR is not modified. A return value \fB0\fR means the ioctl is timed out. In this case, the memory content pointed by \fBdp_fds\fR is not modified. If the call is successful, it returns the number of valid \fBpollfd\fR entries in the array pointed by \fBdp_fds\fR; the contents of the rest of the buffer is undefined. For each valid \fBpollfd\fR entry, the \fBfd\fR field indicates the file descriptor on which the polled \fBevents\fR happened. The \fBevents\fR field is the user specified \fBpoll\fR \fBevents\fR. The \fBrevents\fR field contains the \fBevents\fR occurred. \fB-1\fR is returned if the call fails. .sp .LP \fBDP_ISPOLLED\fR ioctl allows you to query if a file descriptor is already in the monitored set represented by \fBfd\fR. The \fBfd\fR field of the \fBpollfd\fR structure indicates the file descriptor of interest. The \fBDP_ISPOLLED\fR ioctl returns \fB1\fR if the file descriptor is in the set. The \fBevents\fR field contains \fB0\fR. The \fBrevents\fR field contains the currently polled \fBevents\fR. The ioctl returns \fB0\fR if the file descriptor is not in the set. The \fBpollfd\fR structure pointed by \fIpfd\fR is not modified. The ioctl returns a \fB-1\fR if the call fails. .SH EXAMPLES The following example shows how \fB/dev/poll\fR may be used. .sp .in +2 .nf { ... /* * open the driver */ if ((wfd = open("/dev/poll", O_RDWR)) < 0) { exit(-1); } pollfd = (struct pollfd* )malloc(sizeof(struct pollfd) * MAXBUF); if (pollfd == NULL) { close(wfd); exit(-1); } /* * initialize buffer */ for (i = 0; i < MAXBUF; i++) { pollfd[i].fd = fds[i]; pollfd[i].events = POLLIN; pollfd[i].revents = 0; } if (write(wfd, &pollfd[0], sizeof(struct pollfd) * MAXBUF) != sizeof(struct pollfd) * MAXBUF) { perror("failed to write all pollfds"); close (wfd); free(pollfd); exit(-1); } /* * read from the devpoll driver */ dopoll.dp_timeout = -1; dopoll.dp_nfds = MAXBUF; dopoll.dp_fds = pollfd; result = ioctl(wfd, DP_POLL, &dopoll); if (result < 0) { perror("/dev/poll ioctl DP_POLL failed"); close (wfd); free(pollfd); exit(-1); } for (i = 0; i < result; i++) { read(dopoll.dp_fds[i].fd, rbuf, STRLEN); } ... } .fi .in -2 .sp .LP The following example is part of a test program which shows how \fBDP_ISPOLLED()\fR ioctl may be used. .sp .in +2 .nf { ... loopcnt = 0; while (loopcnt < ITERATION) { rn = random(); rn %= RANGE; if (write(fds[rn], TESTSTRING, strlen(TESTSTRING)) != strlen(TESTSTRING)) { perror("write to fifo failed."); close (wfd); free(pollfd); error = 1; goto out1; } dpfd.fd = fds[rn]; dpfd.events = 0; dpfd.revents = 0; result = ioctl(wfd, DP_ISPOLLED, &dpfd); if (result < 0) { perror("/dev/poll ioctl DP_ISPOLLED failed"); printf("errno = %d\en", errno); close (wfd); free(pollfd); error = 1; goto out1; } if (result != 1) { printf("DP_ISPOLLED returned incorrect result: %d.\en", result); close (wfd); free(pollfd); error = 1; goto out1; } if (dpfd.fd != fds[rn]) { printf("DP_ISPOLLED returned wrong fd %d, expect %d\en", dpfd.fd, fds[rn]); close (wfd); free(pollfd); error = 1; goto out1; } if (dpfd.revents != POLLIN) { printf("DP_ISPOLLED returned unexpected revents %d\en", dpfd.revents); close (wfd); free(pollfd); error = 1; goto out1; } if (read(dpfd.fd, rbuf, strlen(TESTSTRING)) != strlen(TESTSTRING)) { perror("read from fifo failed"); close (wfd); free(pollfd); error = 1; goto out1; } loopcnt++; } .fi .in -2 .SH ERRORS .ne 2 .na \fB\fBEACCES\fR \fR .ad .RS 11n A process does not have permission to access the content cached in \fB/dev/poll\fR. .RE .sp .ne 2 .na \fB\fBEINTR\fR \fR .ad .RS 11n A signal was caught during the execution of the \fBioctl\fR(2) function. .RE .sp .ne 2 .na \fB\fBEFAULT\fR \fR .ad .RS 11n The request argument requires a data transfer to or from a buffer pointed to by \fIarg\fR, but \fIarg\fR points to an illegal address. .RE .sp .ne 2 .na \fB\fBEINVAL\fR \fR .ad .RS 11n The request or \fIarg\fR parameter is not valid for this device, or field of the dvpoll struct pointed by \fIarg\fR is not valid (for example, when using write/pwrite dp_nfds is greater than {OPEN_MAX}, or when using the DPPOLL ioctl dp_nfds is greater than or equal to {OPEN_MAX}}. .RE .sp .ne 2 .na \fB\fBENXIO\fR \fR .ad .RS 11n The \fBO_NONBLOCK\fR flag is set, the named file is a FIFO, the \fBO_WRONLY\fR flag is set, and no process has the file open for reading; or the named file is a character special or block special file and the device associated with this special file does not exist. .RE .SH ATTRIBUTES See \fBattributes\fR(7) for a description of the following attributes: .sp .sp .TS box; l l l l . ATTRIBUTE TYPE ATTRIBUTE VALUE Architecture SPARC, x86 Interface Stability Obsolete MT-Level Safe .TE .SH SEE ALSO .BR open (2), .BR poll (2), .BR write (2), .BR attributes (7) .SH NOTES The \fB/dev/poll\fR API is particularly beneficial to applications that poll a large number of file descriptors repeatedly. Applications will exhibit the best performance gain if the polled file descriptor list rarely change. .sp .LP When using the \fB/dev/poll\fR driver, you should remove a closed file descriptor from a monitored poll set. Failure to do so may result in a \fBPOLLNVAL\fR \fBrevents\fR being returned for the closed file descriptor. When a file descriptor is closed but not removed from the monitored set, and is reused in subsequent open of a different device, you will be polling the device associated with the reused file descriptor. In a multithreaded application, careful coordination among threads doing close and \fBDP_POLL\fR ioctl is recommended for consistent results. .sp .LP The \fB/dev/poll\fR driver caches a list of polled file descriptors, which are specific to a process. Therefore, the \fB/dev/poll\fR file descriptor of a process will be inherited by its child process, just like any other file descriptors. But the child process will have very limited access through this inherited \fB/dev/poll\fR file descriptor. Any attempt to write or do ioctl by the child process will result in an \fBEACCES\fR error. The child process should close the inherited \fB/dev/poll\fR file descriptor and open its own if desired. .sp .LP The \fB/dev/poll\fR driver does not yet support polling. Polling on a \fB/dev/poll\fR file descriptor will result in \fBPOLLERR\fR being returned in the \fBrevents\fR field of \fBpollfd\fR structure.