From 9c3060bedd84144653a2ad7bea32389f65598d40 Mon Sep 17 00:00:00 2001 From: Davide Libenzi Date: Thu, 10 May 2007 22:23:21 -0700 Subject: [PATCH] signal/timer/event: KAIO eventfd support example This is an example about how to add eventfd support to the current KAIO code, in order to enable KAIO to post readiness events to a pollable fd (hence compatible with POSIX select/poll). The KAIO code simply signals the eventfd fd when events are ready, and this triggers a POLLIN in the fd. This patch uses a reserved for future use member of the struct iocb to pass an eventfd file descriptor, that KAIO will use to post events every time a request completes. At that point, an aio_getevents() will return the completed result to a struct io_event. I made a quick test program to verify the patch, and it runs fine here: http://www.xmailserver.org/eventfd-aio-test.c The test program uses poll(2), but it'd, of course, work with select and epoll too. This can allow to schedule both block I/O and other poll-able devices requests, and wait for results using select/poll/epoll. In a typical scenario, an application would submit KAIO request using aio_submit(), and will also use epoll_ctl() on the whole other class of devices (that with the addition of signals, timers and user events, now it's pretty much complete), and then would: epoll_wait(...); for_each_event { if (curr_event_is_kaiofd) { aio_getevents(); dispatch_aio_events(); } else { dispatch_epoll_event(); } } Signed-off-by: Davide Libenzi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/aio.c | 28 ++++++++++++++++++++++++++-- include/linux/aio.h | 6 ++++++ include/linux/aio_abi.h | 18 +++++++++++++++++- 3 files changed, 49 insertions(+), 3 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index ac1c1587aa..dbe699e982 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -30,6 +30,7 @@ #include #include #include +#include #include #include @@ -417,6 +418,7 @@ static struct kiocb fastcall *__aio_get_req(struct kioctx *ctx) req->private = NULL; req->ki_iovec = NULL; INIT_LIST_HEAD(&req->ki_run_list); + req->ki_eventfd = ERR_PTR(-EINVAL); /* Check if the completion queue has enough free space to * accept an event from this io. @@ -458,6 +460,8 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req) { assert_spin_locked(&ctx->ctx_lock); + if (!IS_ERR(req->ki_eventfd)) + fput(req->ki_eventfd); if (req->ki_dtor) req->ki_dtor(req); if (req->ki_iovec != &req->ki_inline_vec) @@ -942,6 +946,14 @@ int fastcall aio_complete(struct kiocb *iocb, long res, long res2) return 1; } + /* + * Check if the user asked us to deliver the result through an + * eventfd. The eventfd_signal() function is safe to be called + * from IRQ context. + */ + if (!IS_ERR(iocb->ki_eventfd)) + eventfd_signal(iocb->ki_eventfd, 1); + info = &ctx->ring_info; /* add a completion event to the ring buffer. @@ -1526,8 +1538,7 @@ int fastcall io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb, ssize_t ret; /* enforce forwards compatibility on users */ - if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2 || - iocb->aio_reserved3)) { + if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2)) { pr_debug("EINVAL: io_submit: reserve field set\n"); return -EINVAL; } @@ -1551,6 +1562,19 @@ int fastcall io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb, fput(file); return -EAGAIN; } + if (iocb->aio_flags & IOCB_FLAG_RESFD) { + /* + * If the IOCB_FLAG_RESFD flag of aio_flags is set, get an + * instance of the file* now. The file descriptor must be + * an eventfd() fd, and will be signaled for each completed + * event using the eventfd_signal() function. + */ + req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd); + if (unlikely(IS_ERR(req->ki_eventfd))) { + ret = PTR_ERR(req->ki_eventfd); + goto out_put_req; + } + } req->ki_filp = file; ret = put_user(req->ki_key, &user_iocb->aio_key); diff --git a/include/linux/aio.h b/include/linux/aio.h index 43dc2ebfaa..b903fc02bd 100644 --- a/include/linux/aio.h +++ b/include/linux/aio.h @@ -119,6 +119,12 @@ struct kiocb { struct list_head ki_list; /* the aio core uses this * for cancellation */ + + /* + * If the aio_resfd field of the userspace iocb is not zero, + * this is the underlying file* to deliver event to. + */ + struct file *ki_eventfd; }; #define is_sync_kiocb(iocb) ((iocb)->ki_key == KIOCB_SYNC_KEY) diff --git a/include/linux/aio_abi.h b/include/linux/aio_abi.h index e3ca0a485c..9e01729313 100644 --- a/include/linux/aio_abi.h +++ b/include/linux/aio_abi.h @@ -45,6 +45,14 @@ enum { IOCB_CMD_PWRITEV = 8, }; +/* + * Valid flags for the "aio_flags" member of the "struct iocb". + * + * IOCB_FLAG_RESFD - Set if the "aio_resfd" member of the "struct iocb" + * is valid. + */ +#define IOCB_FLAG_RESFD (1 << 0) + /* read() from /dev/aio returns these structures. */ struct io_event { __u64 data; /* the data field from the iocb */ @@ -84,7 +92,15 @@ struct iocb { /* extra parameters */ __u64 aio_reserved2; /* TODO: use this for a (struct sigevent *) */ - __u64 aio_reserved3; + + /* flags for the "struct iocb" */ + __u32 aio_flags; + + /* + * if the IOCB_FLAG_RESFD flag of "aio_flags" is set, this is an + * eventfd to signal AIO readiness to + */ + __u32 aio_resfd; }; /* 64 bytes */ #undef IFBIG -- 2.39.5