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/*
* File descriptors management functions.
*
* Copyright 2000-2012 Willy Tarreau <w@1wt.eu>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* This code implements "speculative I/O". The principle is to try to perform
* expected I/O before registering the events in the poller. Each time this
* succeeds, it saves a possibly expensive system call to set the event. It
* generally succeeds for all reads after an accept(), and for writes after a
* connect(). It also improves performance for streaming connections because
* even if only one side is polled, the other one may react accordingly
* depending on the fill level of the buffer. This behaviour is also the only
* one compatible with event-based pollers (eg: EPOLL_ET).
*
* More importantly, it enables I/O operations that are backed by invisible
* buffers. For example, SSL is able to read a whole socket buffer and not
* deliver it to the application buffer because it's full. Unfortunately, it
* won't be reported by a poller anymore until some new activity happens. The
* only way to call it again thus is to perform speculative I/O as soon as
* reading on the FD is enabled again.
*
* The speculative I/O uses a list of expected events and a list of updates.
* Expected events are events that are expected to come and that we must report
* to the application until it asks to stop or to poll. Updates are new requests
* for changing an FD state. Updates are the only way to create new events. This
* is important because it means that the number of speculative events cannot
* increase between updates and will only grow one at a time while processing
* updates. All updates must always be processed, though events might be
* processed by small batches if required.
*
* There is no direct link between the FD and the updates list. There is only a
* bit in the fdtab[] to indicate than a file descriptor is already present in
* the updates list. Once an fd is present in the updates list, it will have to
* be considered even if its changes are reverted in the middle or if the fd is
* replaced.
*
* It is important to understand that as long as all expected events are
* processed, they might starve the polled events, especially because polled
* I/O starvation quickly induces more speculative I/O. One solution to this
* consists in only processing a part of the events at once, but one drawback
* is that unhandled events will still wake the poller up. Using an event-driven
* poller such as EPOLL_ET will solve this issue though.
*
* A file descriptor has a distinct state for each direction. This state is a
* combination of two bits :
* bit 0 = active Y/N : is set if the FD is active, which means that its
* handler will be called without prior polling ;
* bit 1 = polled Y/N : is set if the FD was subscribed to polling
*
* It is perfectly valid to have both bits set at a time, which generally means
* that the FD was reported by polling, was marked active and not yet unpolled.
* Such a state must not last long to avoid unneeded wakeups.
*
* The state of the FD as of last change is preserved in two other bits. These
* ones are useful to save a significant amount of system calls during state
* changes, because there is no need to update the FD status in the system until
* we're about to call the poller.
*
* Since we do not want to scan all the FD list to find speculative I/O events,
* we store them in a list consisting in a linear array holding only the FD
* indexes right now. Note that a closed FD cannot exist in the spec list,
* because it is closed by fd_delete() which in turn calls __fd_clo() which
* always removes it from the list.
*
* For efficiency reasons, we will store the Read and Write bits interlaced to
* form a 4-bit field, so that we can simply shift the value right by 0/1 and
* get what we want :
* 3 2 1 0
* Wp Rp Wa Ra
*
* The FD array has to hold a back reference to the speculative list. This
* reference is always valid unless the FD if currently being polled and not
* updated (in which case the reference points to index 0).
*
* We store the FD state in the 4 lower bits of fdtab[fd].spec_e, and save the
* previous state upon changes in the 4 higher bits, so that changes are easy
* to spot.
*/
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <common/compat.h>
#include <common/config.h>
#include <types/global.h>
#include <proto/fd.h>
#include <proto/port_range.h>
struct fdtab *fdtab = NULL; /* array of all the file descriptors */
struct fdinfo *fdinfo = NULL; /* less-often used infos for file descriptors */
int maxfd; /* # of the highest fd + 1 */
int totalconn; /* total # of terminated sessions */
int actconn; /* # of active sessions */
struct poller pollers[MAX_POLLERS];
struct poller cur_poller;
int nbpollers = 0;
/* FD status is defined by the poller's status and by the speculative I/O list */
int fd_nbspec = 0; // number of speculative events in the list
int fd_nbupdt = 0; // number of updates in the list
unsigned int *fd_spec = NULL; // speculative I/O list
unsigned int *fd_updt = NULL; // FD updates list
/* Deletes an FD from the fdsets, and recomputes the maxfd limit.
* The file descriptor is also closed.
*/
void fd_delete(int fd)
{
if (cur_poller.clo)
cur_poller.clo(fd);
release_spec_entry(fd);
fdtab[fd].spec_e &= ~(FD_EV_CURR_MASK | FD_EV_PREV_MASK);
port_range_release_port(fdinfo[fd].port_range, fdinfo[fd].local_port);
fdinfo[fd].port_range = NULL;
close(fd);
fdtab[fd].owner = NULL;
fdtab[fd].new = 0;
while ((maxfd-1 >= 0) && !fdtab[maxfd-1].owner)
maxfd--;
}
/* Scan and process the speculative events. This should be called right after
* the poller.
*/
void fd_process_spec_events()
{
int fd, spec_idx, e;
/* now process speculative events if any */
for (spec_idx = 0; spec_idx < fd_nbspec; ) {
fd = fd_spec[spec_idx];
e = fdtab[fd].spec_e;
/*
* Process the speculative events.
*
* Principle: events which are marked FD_EV_ACTIVE are processed
* with their usual I/O callback. The callback may remove the
* events from the list or tag them for polling. Changes will be
* applied on next round.
*/
fdtab[fd].ev &= FD_POLL_STICKY;
if (e & FD_EV_ACTIVE_R)
fdtab[fd].ev |= FD_POLL_IN;
if (e & FD_EV_ACTIVE_W)
fdtab[fd].ev |= FD_POLL_OUT;
if (fdtab[fd].iocb && fdtab[fd].owner && fdtab[fd].ev)
fdtab[fd].iocb(fd);
/* if the fd was removed from the spec list, it has been
* replaced by the next one that we don't want to skip !
*/
if (spec_idx < fd_nbspec && fd_spec[spec_idx] != fd)
continue;
spec_idx++;
}
}
/* disable the specified poller */
void disable_poller(const char *poller_name)
{
int p;
for (p = 0; p < nbpollers; p++)
if (strcmp(pollers[p].name, poller_name) == 0)
pollers[p].pref = 0;
}
/*
* Initialize the pollers till the best one is found.
* If none works, returns 0, otherwise 1.
*/
int init_pollers()
{
int p;
struct poller *bp;
if ((fd_spec = (uint32_t *)calloc(1, sizeof(uint32_t) * global.maxsock)) == NULL)
goto fail_spec;
if ((fd_updt = (uint32_t *)calloc(1, sizeof(uint32_t) * global.maxsock)) == NULL)
goto fail_updt;
do {
bp = NULL;
for (p = 0; p < nbpollers; p++)
if (!bp || (pollers[p].pref > bp->pref))
bp = &pollers[p];
if (!bp || bp->pref == 0)
break;
if (bp->init(bp)) {
memcpy(&cur_poller, bp, sizeof(*bp));
return 1;
}
} while (!bp || bp->pref == 0);
return 0;
fail_updt:
free(fd_spec);
fail_spec:
return 0;
}
/*
* Deinitialize the pollers.
*/
void deinit_pollers() {
struct poller *bp;
int p;
for (p = 0; p < nbpollers; p++) {
bp = &pollers[p];
if (bp && bp->pref)
bp->term(bp);
}
free(fd_updt);
free(fd_spec);
fd_updt = NULL;
fd_spec = NULL;
}
/*
* Lists the known pollers on <out>.
* Should be performed only before initialization.
*/
int list_pollers(FILE *out)
{
int p;
int last, next;
int usable;
struct poller *bp;
fprintf(out, "Available polling systems :\n");
usable = 0;
bp = NULL;
last = next = -1;
while (1) {
for (p = 0; p < nbpollers; p++) {
if ((next < 0 || pollers[p].pref > next)
&& (last < 0 || pollers[p].pref < last)) {
next = pollers[p].pref;
if (!bp || (pollers[p].pref > bp->pref))
bp = &pollers[p];
}
}
if (next == -1)
break;
for (p = 0; p < nbpollers; p++) {
if (pollers[p].pref == next) {
fprintf(out, " %10s : ", pollers[p].name);
if (pollers[p].pref == 0)
fprintf(out, "disabled, ");
else
fprintf(out, "pref=%3d, ", pollers[p].pref);
if (pollers[p].test(&pollers[p])) {
fprintf(out, " test result OK");
if (next > 0)
usable++;
} else {
fprintf(out, " test result FAILED");
if (bp == &pollers[p])
bp = NULL;
}
fprintf(out, "\n");
}
}
last = next;
next = -1;
};
fprintf(out, "Total: %d (%d usable), will use %s.\n", nbpollers, usable, bp ? bp->name : "none");
return 0;
}
/*
* Some pollers may lose their connection after a fork(). It may be necessary
* to create initialize part of them again. Returns 0 in case of failure,
* otherwise 1. The fork() function may be NULL if unused. In case of error,
* the the current poller is destroyed and the caller is responsible for trying
* another one by calling init_pollers() again.
*/
int fork_poller()
{
if (cur_poller.fork) {
if (cur_poller.fork(&cur_poller))
return 1;
cur_poller.term(&cur_poller);
return 0;
}
return 1;
}
/*
* Local variables:
* c-indent-level: 8
* c-basic-offset: 8
* End:
*/