1f050a4690
The ppoll(2) and epoll(7) file descriptor monitoring implementations are mixed with the core util/aio-posix.c code. Before adding another implementation for Linux io_uring, extract out the existing ones so there is a clear interface and the core code is simpler. The new interface is AioContext->fdmon_ops, a pointer to a FDMonOps struct. See the patch for details. Semantic changes: 1. ppoll(2) now reflects events from pollfds[] back into AioHandlers while we're still on the clock for adaptive polling. This was already happening for epoll(7), so if it's really an issue then we'll need to fix both in the future. 2. epoll(7)'s fallback to ppoll(2) while external events are disabled was broken when the number of fds exceeded the epoll(7) upgrade threshold. I guess this code path simply wasn't tested and no one noticed the bug. I didn't go out of my way to fix it but the correct code is simpler than preserving the bug. I also took some liberties in removing the unnecessary AioContext->epoll_available (just check AioContext->epollfd != -1 instead) and AioContext->epoll_enabled (it's implicit if our AioContext->fdmon_ops callbacks are being invoked) fields. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Link: https://lore.kernel.org/r/20200305170806.1313245-4-stefanha@redhat.com Message-Id: <20200305170806.1313245-4-stefanha@redhat.com>
105 lines
2.8 KiB
C
105 lines
2.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* poll(2) file descriptor monitoring
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*
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* Uses ppoll(2) when available, g_poll() otherwise.
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*/
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#include "qemu/osdep.h"
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#include "aio-posix.h"
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#include "qemu/rcu_queue.h"
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/*
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* These thread-local variables are used only in fdmon_poll_wait() around the
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* call to the poll() system call. In particular they are not used while
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* aio_poll is performing callbacks, which makes it much easier to think about
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* reentrancy!
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*
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* Stack-allocated arrays would be perfect but they have size limitations;
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* heap allocation is expensive enough that we want to reuse arrays across
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* calls to aio_poll(). And because poll() has to be called without holding
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* any lock, the arrays cannot be stored in AioContext. Thread-local data
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* has none of the disadvantages of these three options.
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*/
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static __thread GPollFD *pollfds;
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static __thread AioHandler **nodes;
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static __thread unsigned npfd, nalloc;
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static __thread Notifier pollfds_cleanup_notifier;
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static void pollfds_cleanup(Notifier *n, void *unused)
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{
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g_assert(npfd == 0);
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g_free(pollfds);
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g_free(nodes);
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nalloc = 0;
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}
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static void add_pollfd(AioHandler *node)
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{
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if (npfd == nalloc) {
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if (nalloc == 0) {
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pollfds_cleanup_notifier.notify = pollfds_cleanup;
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qemu_thread_atexit_add(&pollfds_cleanup_notifier);
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nalloc = 8;
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} else {
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g_assert(nalloc <= INT_MAX);
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nalloc *= 2;
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}
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pollfds = g_renew(GPollFD, pollfds, nalloc);
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nodes = g_renew(AioHandler *, nodes, nalloc);
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}
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nodes[npfd] = node;
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pollfds[npfd] = (GPollFD) {
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.fd = node->pfd.fd,
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.events = node->pfd.events,
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};
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npfd++;
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}
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static int fdmon_poll_wait(AioContext *ctx, AioHandlerList *ready_list,
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int64_t timeout)
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{
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AioHandler *node;
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int ret;
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assert(npfd == 0);
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QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
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if (!QLIST_IS_INSERTED(node, node_deleted) && node->pfd.events
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&& aio_node_check(ctx, node->is_external)) {
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add_pollfd(node);
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}
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}
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/* epoll(7) is faster above a certain number of fds */
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if (fdmon_epoll_try_upgrade(ctx, npfd)) {
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return ctx->fdmon_ops->wait(ctx, ready_list, timeout);
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}
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ret = qemu_poll_ns(pollfds, npfd, timeout);
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if (ret > 0) {
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int i;
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for (i = 0; i < npfd; i++) {
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int revents = pollfds[i].revents;
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if (revents) {
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aio_add_ready_handler(ready_list, nodes[i], revents);
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}
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}
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}
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npfd = 0;
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return ret;
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}
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static void fdmon_poll_update(AioContext *ctx, AioHandler *node, bool is_new)
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{
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/* Do nothing, AioHandler already contains the state we'll need */
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}
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const FDMonOps fdmon_poll_ops = {
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.update = fdmon_poll_update,
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.wait = fdmon_poll_wait,
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};
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