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eventfd - allow atomic read and waitqueue remove
KVM needs a wait to atomically remove themselves from the eventfd ->poll() wait queue head, in order to handle correctly their IRQfd deassign operation. This patch introduces such API, plus a way to read an eventfd from its context. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Avi Kivity <avi@redhat.com>
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parent
a6085fbaf6
commit
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2 changed files with 90 additions and 15 deletions
89
fs/eventfd.c
89
fs/eventfd.c
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@ -135,26 +135,71 @@ static unsigned int eventfd_poll(struct file *file, poll_table *wait)
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return events;
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return events;
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}
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}
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static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
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static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
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loff_t *ppos)
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{
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*cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
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ctx->count -= *cnt;
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}
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/**
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* eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
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* @ctx: [in] Pointer to eventfd context.
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* @wait: [in] Wait queue to be removed.
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* @cnt: [out] Pointer to the 64bit conter value.
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*
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* Returns zero if successful, or the following error codes:
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*
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* -EAGAIN : The operation would have blocked.
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*
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* This is used to atomically remove a wait queue entry from the eventfd wait
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* queue head, and read/reset the counter value.
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*/
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int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
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__u64 *cnt)
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{
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unsigned long flags;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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eventfd_ctx_do_read(ctx, cnt);
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__remove_wait_queue(&ctx->wqh, wait);
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if (*cnt != 0 && waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, POLLOUT);
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return *cnt != 0 ? 0 : -EAGAIN;
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
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/**
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* eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
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* @ctx: [in] Pointer to eventfd context.
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* @no_wait: [in] Different from zero if the operation should not block.
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* @cnt: [out] Pointer to the 64bit conter value.
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*
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* Returns zero if successful, or the following error codes:
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*
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* -EAGAIN : The operation would have blocked but @no_wait was nonzero.
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* -ERESTARTSYS : A signal interrupted the wait operation.
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*
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* If @no_wait is zero, the function might sleep until the eventfd internal
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* counter becomes greater than zero.
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*/
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ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
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{
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{
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struct eventfd_ctx *ctx = file->private_data;
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ssize_t res;
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ssize_t res;
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__u64 ucnt = 0;
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DECLARE_WAITQUEUE(wait, current);
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DECLARE_WAITQUEUE(wait, current);
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if (count < sizeof(ucnt))
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return -EINVAL;
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spin_lock_irq(&ctx->wqh.lock);
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spin_lock_irq(&ctx->wqh.lock);
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*cnt = 0;
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res = -EAGAIN;
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res = -EAGAIN;
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if (ctx->count > 0)
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if (ctx->count > 0)
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res = sizeof(ucnt);
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res = 0;
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else if (!(file->f_flags & O_NONBLOCK)) {
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else if (!no_wait) {
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__add_wait_queue(&ctx->wqh, &wait);
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__add_wait_queue(&ctx->wqh, &wait);
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for (res = 0;;) {
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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set_current_state(TASK_INTERRUPTIBLE);
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if (ctx->count > 0) {
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if (ctx->count > 0) {
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res = sizeof(ucnt);
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res = 0;
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break;
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break;
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}
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}
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if (signal_pending(current)) {
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if (signal_pending(current)) {
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@ -168,18 +213,32 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
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__remove_wait_queue(&ctx->wqh, &wait);
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__remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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__set_current_state(TASK_RUNNING);
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}
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}
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if (likely(res > 0)) {
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if (likely(res == 0)) {
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ucnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
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eventfd_ctx_do_read(ctx, cnt);
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ctx->count -= ucnt;
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if (waitqueue_active(&ctx->wqh))
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, POLLOUT);
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wake_up_locked_poll(&ctx->wqh, POLLOUT);
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}
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}
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spin_unlock_irq(&ctx->wqh.lock);
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spin_unlock_irq(&ctx->wqh.lock);
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if (res > 0 && put_user(ucnt, (__u64 __user *) buf))
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return -EFAULT;
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return res;
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return res;
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}
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_read);
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static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct eventfd_ctx *ctx = file->private_data;
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ssize_t res;
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__u64 cnt;
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if (count < sizeof(cnt))
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return -EINVAL;
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res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
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if (res < 0)
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return res;
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return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
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}
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static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
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static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
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loff_t *ppos)
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loff_t *ppos)
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@ -10,6 +10,7 @@
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#include <linux/fcntl.h>
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#include <linux/fcntl.h>
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#include <linux/file.h>
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#include <linux/file.h>
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#include <linux/wait.h>
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/*
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/*
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* CAREFUL: Check include/asm-generic/fcntl.h when defining
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* CAREFUL: Check include/asm-generic/fcntl.h when defining
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@ -34,6 +35,9 @@ struct file *eventfd_fget(int fd);
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struct eventfd_ctx *eventfd_ctx_fdget(int fd);
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struct eventfd_ctx *eventfd_ctx_fdget(int fd);
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struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
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struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
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int eventfd_signal(struct eventfd_ctx *ctx, int n);
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int eventfd_signal(struct eventfd_ctx *ctx, int n);
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ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt);
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int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
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__u64 *cnt);
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#else /* CONFIG_EVENTFD */
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#else /* CONFIG_EVENTFD */
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@ -61,6 +65,18 @@ static inline void eventfd_ctx_put(struct eventfd_ctx *ctx)
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}
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}
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static inline ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait,
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__u64 *cnt)
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{
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return -ENOSYS;
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}
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static inline int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx,
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wait_queue_t *wait, __u64 *cnt)
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{
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return -ENOSYS;
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}
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#endif
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#endif
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#endif /* _LINUX_EVENTFD_H */
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#endif /* _LINUX_EVENTFD_H */
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