Linux poll mechanism

1. User space Invocation (ref. poll (2)-Linux man page)

int poll (struct POLLFD *fds, nfds_t nfds, int timeout);

It waits for one of a set of the file descriptors to become ready to perform I/O.

The set of file descriptors to be monitored are specified in the fds argument, which are an array of structures of The following form:

struct POLLFD {    int   FD;         /*  */short     events;     /*  */short     revents;    /* */};

A description of the timeout parameter:

Timeout>0, set timeout time to timeout

Timeout=0, return directly

Timeout<0, unlimited long timeout time

Return Value Description:

On success, a positive number is returned; This is the number of structures which has nonzero revents fields (in other words, those descriptors with events or error S reported).

A value of 0 indicates the call timed out and no file descriptors were ready. On error, 1 are returned, and errno is set appropriately.

2. Kernel calls

long sys_poll (structint Nfds,long  timeout_msecs)    -->ret = Do_ Sys_poll (UFDs, Nfds, &timeout);         --struct  poll_wqueues table        ; -->poll_initwait (&table);             -->init_poll_funcptr (&pwq->pt, __pollwait);         -->fdcount = Do_poll (Nfds, head, &table, timeout);             --DO_POLLFD (PFD, PT                )--andif (file->f_op && file->f_op->poll)

2.1

Linux poll mechanism