/* * QEMU aio implementation * * Copyright IBM, Corp. 2008 * * Authors: * Anthony Liguori <aliguori@us.ibm.com> * * This work is licensed under the terms of the GNU GPL, version 2. See * the COPYING file in the top-level directory. * * Contributions after 2012-01-13 are licensed under the terms of the * GNU GPL, version 2 or (at your option) any later version. */ #include "qemu-common.h" #include "block/block.h" #include "qemu/queue.h" #include "qemu/sockets.h" struct AioHandler { GPollFD pfd; IOHandler *io_read; IOHandler *io_write; int deleted; void *opaque; QLIST_ENTRY(AioHandler) node; }; static AioHandler *find_aio_handler(AioContext *ctx, int fd) { AioHandler *node; QLIST_FOREACH(node, &ctx->aio_handlers, node) { if (node->pfd.fd == fd) if (!node->deleted) return node; } return NULL; } void aio_set_fd_handler(AioContext *ctx, int fd, IOHandler *io_read, IOHandler *io_write, void *opaque) { AioHandler *node; node = find_aio_handler(ctx, fd); /* Are we deleting the fd handler? */ if (!io_read && !io_write) { if (node) { g_source_remove_poll(&ctx->source, &node->pfd); /* If the lock is held, just mark the node as deleted */ if (ctx->walking_handlers) { node->deleted = 1; node->pfd.revents = 0; } else { /* Otherwise, delete it for real. We can't just mark it as * deleted because deleted nodes are only cleaned up after * releasing the walking_handlers lock. */ QLIST_REMOVE(node, node); g_free(node); } } } else { if (node == NULL) { /* Alloc and insert if it's not already there */ node = g_new0(AioHandler, 1); node->pfd.fd = fd; QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node); g_source_add_poll(&ctx->source, &node->pfd); } /* Update handler with latest information */ node->io_read = io_read; node->io_write = io_write; node->opaque = opaque; node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0); node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0); } aio_notify(ctx); } void aio_set_event_notifier(AioContext *ctx, EventNotifier *notifier, EventNotifierHandler *io_read) { aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), (IOHandler *)io_read, NULL, notifier); } bool aio_prepare(AioContext *ctx) { return false; } bool aio_pending(AioContext *ctx) { AioHandler *node; QLIST_FOREACH(node, &ctx->aio_handlers, node) { int revents; revents = node->pfd.revents & node->pfd.events; if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) { return true; } if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) { return true; } } return false; } bool aio_dispatch(AioContext *ctx) { AioHandler *node; bool progress = false; /* * If there are callbacks left that have been queued, we need to call them. * Do not call select in this case, because it is possible that the caller * does not need a complete flush (as is the case for aio_poll loops). */ if (aio_bh_poll(ctx)) { progress = true; } /* * We have to walk very carefully in case aio_set_fd_handler is * called while we're walking. */ node = QLIST_FIRST(&ctx->aio_handlers); while (node) { AioHandler *tmp; int revents; ctx->walking_handlers++; revents = node->pfd.revents & node->pfd.events; node->pfd.revents = 0; if (!node->deleted && (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) && node->io_read) { node->io_read(node->opaque); /* aio_notify() does not count as progress */ if (node->opaque != &ctx->notifier) { progress = true; } } if (!node->deleted && (revents & (G_IO_OUT | G_IO_ERR)) && node->io_write) { node->io_write(node->opaque); progress = true; } tmp = node; node = QLIST_NEXT(node, node); ctx->walking_handlers--; if (!ctx->walking_handlers && tmp->deleted) { QLIST_REMOVE(tmp, node); g_free(tmp); } } /* Run our timers */ progress |= timerlistgroup_run_timers(&ctx->tlg); return progress; } /* These thread-local variables are used only in a small part of aio_poll * around the call to the poll() system call. In particular they are not * used while aio_poll is performing callbacks, which makes it much easier * to think about reentrancy! * * Stack-allocated arrays would be perfect but they have size limitations; * heap allocation is expensive enough that we want to reuse arrays across * calls to aio_poll(). And because poll() has to be called without holding * any lock, the arrays cannot be stored in AioContext. Thread-local data * has none of the disadvantages of these three options. */ static __thread GPollFD *pollfds; static __thread AioHandler **nodes; static __thread unsigned npfd, nalloc; static __thread Notifier pollfds_cleanup_notifier; static void pollfds_cleanup(Notifier *n, void *unused) { g_assert(npfd == 0); g_free(pollfds); g_free(nodes); nalloc = 0; } static void add_pollfd(AioHandler *node) { if (npfd == nalloc) { if (nalloc == 0) { pollfds_cleanup_notifier.notify = pollfds_cleanup; qemu_thread_atexit_add(&pollfds_cleanup_notifier); nalloc = 8; } else { g_assert(nalloc <= INT_MAX); nalloc *= 2; } pollfds = g_renew(GPollFD, pollfds, nalloc); nodes = g_renew(AioHandler *, nodes, nalloc); } nodes[npfd] = node; pollfds[npfd] = (GPollFD) { .fd = node->pfd.fd, .events = node->pfd.events, }; npfd++; } bool aio_poll(AioContext *ctx, bool blocking) { AioHandler *node; bool was_dispatching; int i, ret; bool progress; int64_t timeout; aio_context_acquire(ctx); was_dispatching = ctx->dispatching; progress = false; /* aio_notify can avoid the expensive event_notifier_set if * everything (file descriptors, bottom halves, timers) will * be re-evaluated before the next blocking poll(). This is * already true when aio_poll is called with blocking == false; * if blocking == true, it is only true after poll() returns. * * If we're in a nested event loop, ctx->dispatching might be true. * In that case we can restore it just before returning, but we * have to clear it now. */ aio_set_dispatching(ctx, !blocking); ctx->walking_handlers++; assert(npfd == 0); /* fill pollfds */ QLIST_FOREACH(node, &ctx->aio_handlers, node) { if (!node->deleted && node->pfd.events) { add_pollfd(node); } } timeout = blocking ? aio_compute_timeout(ctx) : 0; /* wait until next event */ if (timeout) { aio_context_release(ctx); } ret = qemu_poll_ns((GPollFD *)pollfds, npfd, timeout); if (timeout) { aio_context_acquire(ctx); } /* if we have any readable fds, dispatch event */ if (ret > 0) { for (i = 0; i < npfd; i++) { nodes[i]->pfd.revents = pollfds[i].revents; } } npfd = 0; ctx->walking_handlers--; /* Run dispatch even if there were no readable fds to run timers */ aio_set_dispatching(ctx, true); if (aio_dispatch(ctx)) { progress = true; } aio_set_dispatching(ctx, was_dispatching); aio_context_release(ctx); return progress; }