Introduce the aio_add_sqe() API for submitting io_uring requests in the current AioContext. This allows other components in QEMU, like the block layer, to take advantage of io_uring features without creating their own io_uring context.
This API supports nested event loops just like file descriptor monitoring and BHs do. This comes at a complexity cost: CQE callbacks must be placed on a list so that nested event loops can invoke pending CQE callbacks from parent event loops. If you're wondering why CqeHandler exists instead of just a callback function pointer, this is why. Signed-off-by: Stefan Hajnoczi <[email protected]> Reviewed-by: Eric Blake <[email protected]> --- v5: - Replace cqe_handler_bh with FDMonOps->dispatch() [Kevin] - Rename AioHandler->cqe_handler field to ->internal_cqe_handler [Kevin] - Consolidate fdmon-io_uring.c trace-events changes into this commit v2: - Fix pre_sqe -> prep_sqe typo [Eric] - Add #endif terminator comment [Eric] --- include/block/aio.h | 83 +++++++++++++++++++++++++++++++- util/aio-posix.h | 1 + util/aio-posix.c | 9 ++++ util/fdmon-io_uring.c | 109 ++++++++++++++++++++++++++++++++++++------ util/trace-events | 4 ++ 5 files changed, 190 insertions(+), 16 deletions(-) diff --git a/include/block/aio.h b/include/block/aio.h index b266daa58f..05d1bf4036 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -61,6 +61,27 @@ typedef struct LuringState LuringState; /* Is polling disabled? */ bool aio_poll_disabled(AioContext *ctx); +#ifdef CONFIG_LINUX_IO_URING +/* + * Each io_uring request must have a unique CqeHandler that processes the cqe. + * The lifetime of a CqeHandler must be at least from aio_add_sqe() until + * ->cb() invocation. + */ +typedef struct CqeHandler CqeHandler; +struct CqeHandler { + /* Called by the AioContext when the request has completed */ + void (*cb)(CqeHandler *handler); + + /* Used internally, do not access this */ + QSIMPLEQ_ENTRY(CqeHandler) next; + + /* This field is filled in before ->cb() is called */ + struct io_uring_cqe cqe; +}; + +typedef QSIMPLEQ_HEAD(, CqeHandler) CqeHandlerSimpleQ; +#endif /* CONFIG_LINUX_IO_URING */ + /* Callbacks for file descriptor monitoring implementations */ typedef struct { /* @@ -157,6 +178,27 @@ typedef struct { * Called with list_lock incremented. */ void (*gsource_dispatch)(AioContext *ctx, AioHandlerList *ready_list); + +#ifdef CONFIG_LINUX_IO_URING + /** + * add_sqe: Add an io_uring sqe for submission. + * @prep_sqe: invoked with an sqe that should be prepared for submission + * @opaque: user-defined argument to @prep_sqe() + * @cqe_handler: the unique cqe handler associated with this request + * + * The caller's @prep_sqe() function is invoked to fill in the details of + * the sqe. Do not call io_uring_sqe_set_data() on this sqe. + * + * The kernel may see the sqe as soon as @prep_sqe() returns or it may take + * until the next event loop iteration. + * + * This function is called from the current AioContext and is not + * thread-safe. + */ + void (*add_sqe)(AioContext *ctx, + void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque), + void *opaque, CqeHandler *cqe_handler); +#endif /* CONFIG_LINUX_IO_URING */ } FDMonOps; /* @@ -274,7 +316,10 @@ struct AioContext { struct io_uring fdmon_io_uring; AioHandlerSList submit_list; gpointer io_uring_fd_tag; -#endif + + /* Pending callback state for cqe handlers */ + CqeHandlerSimpleQ cqe_handler_ready_list; +#endif /* CONFIG_LINUX_IO_URING */ /* TimerLists for calling timers - one per clock type. Has its own * locking. @@ -782,4 +827,40 @@ void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch); */ void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min, int64_t max, Error **errp); + +#ifdef CONFIG_LINUX_IO_URING +/** + * aio_has_io_uring: Return whether io_uring is available. + * + * io_uring is either available in all AioContexts or in none, so this only + * needs to be called once from within any thread's AioContext. + */ +static inline bool aio_has_io_uring(void) +{ + AioContext *ctx = qemu_get_current_aio_context(); + return ctx->fdmon_ops->add_sqe; +} + +/** + * aio_add_sqe: Add an io_uring sqe for submission. + * @prep_sqe: invoked with an sqe that should be prepared for submission + * @opaque: user-defined argument to @prep_sqe() + * @cqe_handler: the unique cqe handler associated with this request + * + * The caller's @prep_sqe() function is invoked to fill in the details of the + * sqe. Do not call io_uring_sqe_set_data() on this sqe. + * + * The sqe is submitted by the current AioContext. The kernel may see the sqe + * as soon as @prep_sqe() returns or it may take until the next event loop + * iteration. + * + * When the AioContext is destroyed, pending sqes are ignored and their + * CqeHandlers are not invoked. + * + * This function must be called only when aio_has_io_uring() returns true. + */ +void aio_add_sqe(void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque), + void *opaque, CqeHandler *cqe_handler); +#endif /* CONFIG_LINUX_IO_URING */ + #endif diff --git a/util/aio-posix.h b/util/aio-posix.h index dfa1a51c0b..babbfa8314 100644 --- a/util/aio-posix.h +++ b/util/aio-posix.h @@ -36,6 +36,7 @@ struct AioHandler { #ifdef CONFIG_LINUX_IO_URING QSLIST_ENTRY(AioHandler) node_submitted; unsigned flags; /* see fdmon-io_uring.c */ + CqeHandler internal_cqe_handler; /* used for POLL_ADD/POLL_REMOVE */ #endif int64_t poll_idle_timeout; /* when to stop userspace polling */ bool poll_ready; /* has polling detected an event? */ diff --git a/util/aio-posix.c b/util/aio-posix.c index 6ff36b6e51..e24b955fd9 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -806,3 +806,12 @@ void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch) aio_notify(ctx); } + +#ifdef CONFIG_LINUX_IO_URING +void aio_add_sqe(void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque), + void *opaque, CqeHandler *cqe_handler) +{ + AioContext *ctx = qemu_get_current_aio_context(); + ctx->fdmon_ops->add_sqe(ctx, prep_sqe, opaque, cqe_handler); +} +#endif /* CONFIG_LINUX_IO_URING */ diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c index a06bbe2715..4230bf33e3 100644 --- a/util/fdmon-io_uring.c +++ b/util/fdmon-io_uring.c @@ -46,8 +46,10 @@ #include "qemu/osdep.h" #include <poll.h> #include "qapi/error.h" +#include "qemu/defer-call.h" #include "qemu/rcu_queue.h" #include "aio-posix.h" +#include "trace.h" enum { FDMON_IO_URING_ENTRIES = 128, /* sq/cq ring size */ @@ -76,8 +78,8 @@ static inline int pfd_events_from_poll(int poll_events) } /* - * Returns an sqe for submitting a request. Only be called within - * fdmon_io_uring_wait(). + * Returns an sqe for submitting a request. Only called from the AioContext + * thread. */ static struct io_uring_sqe *get_sqe(AioContext *ctx) { @@ -168,23 +170,46 @@ static void fdmon_io_uring_update(AioContext *ctx, } } +static void fdmon_io_uring_add_sqe(AioContext *ctx, + void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque), + void *opaque, CqeHandler *cqe_handler) +{ + struct io_uring_sqe *sqe = get_sqe(ctx); + + prep_sqe(sqe, opaque); + io_uring_sqe_set_data(sqe, cqe_handler); + + trace_fdmon_io_uring_add_sqe(ctx, opaque, sqe->opcode, sqe->fd, sqe->off, + cqe_handler); +} + +static void fdmon_special_cqe_handler(CqeHandler *cqe_handler) +{ + /* + * This is an empty function that is never called. It is used as a function + * pointer to distinguish it from ordinary cqe handlers. + */ +} + static void add_poll_add_sqe(AioContext *ctx, AioHandler *node) { struct io_uring_sqe *sqe = get_sqe(ctx); int events = poll_events_from_pfd(node->pfd.events); io_uring_prep_poll_add(sqe, node->pfd.fd, events); - io_uring_sqe_set_data(sqe, node); + node->internal_cqe_handler.cb = fdmon_special_cqe_handler; + io_uring_sqe_set_data(sqe, &node->internal_cqe_handler); } static void add_poll_remove_sqe(AioContext *ctx, AioHandler *node) { struct io_uring_sqe *sqe = get_sqe(ctx); + CqeHandler *cqe_handler = &node->internal_cqe_handler; #ifdef LIBURING_HAVE_DATA64 - io_uring_prep_poll_remove(sqe, (uintptr_t)node); + io_uring_prep_poll_remove(sqe, (uintptr_t)cqe_handler); #else - io_uring_prep_poll_remove(sqe, node); + io_uring_prep_poll_remove(sqe, cqe_handler); #endif io_uring_sqe_set_data(sqe, NULL); } @@ -219,19 +244,13 @@ static void fill_sq_ring(AioContext *ctx) } } -/* Returns true if a handler became ready */ -static bool process_cqe(AioContext *ctx, - AioHandlerList *ready_list, - struct io_uring_cqe *cqe) +static bool process_cqe_aio_handler(AioContext *ctx, + AioHandlerList *ready_list, + AioHandler *node, + struct io_uring_cqe *cqe) { - AioHandler *node = io_uring_cqe_get_data(cqe); unsigned flags; - /* poll_timeout and poll_remove have a zero user_data field */ - if (!node) { - return false; - } - /* * Deletion can only happen when IORING_OP_POLL_ADD completes. If we race * with enqueue() here then we can safely clear the FDMON_IO_URING_REMOVE @@ -255,6 +274,35 @@ static bool process_cqe(AioContext *ctx, return true; } +/* Returns true if a handler became ready */ +static bool process_cqe(AioContext *ctx, + AioHandlerList *ready_list, + struct io_uring_cqe *cqe) +{ + CqeHandler *cqe_handler = io_uring_cqe_get_data(cqe); + + /* poll_timeout and poll_remove have a zero user_data field */ + if (!cqe_handler) { + return false; + } + + /* + * Special handling for AioHandler cqes. They need ready_list and have a + * return value. + */ + if (cqe_handler->cb == fdmon_special_cqe_handler) { + AioHandler *node = container_of(cqe_handler, AioHandler, + internal_cqe_handler); + return process_cqe_aio_handler(ctx, ready_list, node, cqe); + } + + cqe_handler->cqe = *cqe; + + /* Handlers are invoked later by fdmon_io_uring_dispatch() */ + QSIMPLEQ_INSERT_TAIL(&ctx->cqe_handler_ready_list, cqe_handler, next); + return false; +} + static int process_cq_ring(AioContext *ctx, AioHandlerList *ready_list) { struct io_uring *ring = &ctx->fdmon_io_uring; @@ -297,6 +345,32 @@ static bool fdmon_io_uring_gsource_check(AioContext *ctx) return g_source_query_unix_fd(&ctx->source, tag) & G_IO_IN; } +/* Dispatch CQE handlers that are ready */ +static bool fdmon_io_uring_dispatch(AioContext *ctx) +{ + CqeHandlerSimpleQ *ready_list = &ctx->cqe_handler_ready_list; + bool progress = false; + + /* Handlers may use defer_call() to coalesce frequent operations */ + defer_call_begin(); + + while (!QSIMPLEQ_EMPTY(ready_list)) { + CqeHandler *cqe_handler = QSIMPLEQ_FIRST(ready_list); + + QSIMPLEQ_REMOVE_HEAD(ready_list, next); + + trace_fdmon_io_uring_cqe_handler(ctx, cqe_handler, + cqe_handler->cqe.res); + cqe_handler->cb(cqe_handler); + progress = true; + } + + defer_call_end(); + + return progress; +} + + /* This is where CQEs are processed in the glib event loop */ static void fdmon_io_uring_gsource_dispatch(AioContext *ctx, AioHandlerList *ready_list) @@ -369,9 +443,11 @@ static const FDMonOps fdmon_io_uring_ops = { .update = fdmon_io_uring_update, .wait = fdmon_io_uring_wait, .need_wait = fdmon_io_uring_need_wait, + .dispatch = fdmon_io_uring_dispatch, .gsource_prepare = fdmon_io_uring_gsource_prepare, .gsource_check = fdmon_io_uring_gsource_check, .gsource_dispatch = fdmon_io_uring_gsource_dispatch, + .add_sqe = fdmon_io_uring_add_sqe, }; bool fdmon_io_uring_setup(AioContext *ctx, Error **errp) @@ -387,6 +463,7 @@ bool fdmon_io_uring_setup(AioContext *ctx, Error **errp) } QSLIST_INIT(&ctx->submit_list); + QSIMPLEQ_INIT(&ctx->cqe_handler_ready_list); ctx->fdmon_ops = &fdmon_io_uring_ops; ctx->io_uring_fd_tag = g_source_add_unix_fd(&ctx->source, ctx->fdmon_io_uring.ring_fd, G_IO_IN); @@ -423,6 +500,8 @@ void fdmon_io_uring_destroy(AioContext *ctx) g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag); ctx->io_uring_fd_tag = NULL; + assert(QSIMPLEQ_EMPTY(&ctx->cqe_handler_ready_list)); + qemu_lockcnt_lock(&ctx->list_lock); fdmon_poll_downgrade(ctx); qemu_lockcnt_unlock(&ctx->list_lock); diff --git a/util/trace-events b/util/trace-events index bd8f25fb59..540d662507 100644 --- a/util/trace-events +++ b/util/trace-events @@ -24,6 +24,10 @@ buffer_move_empty(const char *buf, size_t len, const char *from) "%s: %zd bytes buffer_move(const char *buf, size_t len, const char *from) "%s: %zd bytes from %s" buffer_free(const char *buf, size_t len) "%s: capacity %zd" +# fdmon-io_uring.c +fdmon_io_uring_add_sqe(void *ctx, void *opaque, int opcode, int fd, uint64_t off, void *cqe_handler) "ctx %p opaque %p opcode %d fd %d off %"PRId64" cqe_handler %p" +fdmon_io_uring_cqe_handler(void *ctx, void *cqe_handler, int cqe_res) "ctx %p cqe_handler %p cqe_res %d" + # filemonitor-inotify.c qemu_file_monitor_add_watch(void *mon, const char *dirpath, const char *filename, void *cb, void *opaque, int64_t id) "File monitor %p add watch dir='%s' file='%s' cb=%p opaque=%p id=%" PRId64 qemu_file_monitor_remove_watch(void *mon, const char *dirpath, int64_t id) "File monitor %p remove watch dir='%s' id=%" PRId64 -- 2.51.1
