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![Randy Dunlap](/assets/img/avatar_default.png)
Add fs/eventfd.c to filesystems docbook. Make typo corrections in fs/eventfd.c. Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
439 lines
11 KiB
C
439 lines
11 KiB
C
/*
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* fs/eventfd.c
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*
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* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
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*
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*/
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/anon_inodes.h>
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#include <linux/syscalls.h>
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#include <linux/module.h>
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#include <linux/kref.h>
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#include <linux/eventfd.h>
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struct eventfd_ctx {
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struct kref kref;
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wait_queue_head_t wqh;
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/*
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* Every time that a write(2) is performed on an eventfd, the
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* value of the __u64 being written is added to "count" and a
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* wakeup is performed on "wqh". A read(2) will return the "count"
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* value to userspace, and will reset "count" to zero. The kernel
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* side eventfd_signal() also, adds to the "count" counter and
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* issue a wakeup.
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*/
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__u64 count;
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unsigned int flags;
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};
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/**
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* eventfd_signal - Adds @n to the eventfd counter.
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* @ctx: [in] Pointer to the eventfd context.
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* @n: [in] Value of the counter to be added to the eventfd internal counter.
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* The value cannot be negative.
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*
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* This function is supposed to be called by the kernel in paths that do not
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* allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
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* value, and we signal this as overflow condition by returining a POLLERR
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* to poll(2).
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*
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* Returns @n in case of success, a non-negative number lower than @n in case
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* of overflow, or the following error codes:
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*
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* -EINVAL : The value of @n is negative.
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*/
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int eventfd_signal(struct eventfd_ctx *ctx, int n)
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{
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unsigned long flags;
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if (n < 0)
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return -EINVAL;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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if (ULLONG_MAX - ctx->count < n)
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n = (int) (ULLONG_MAX - ctx->count);
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ctx->count += n;
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, POLLIN);
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return n;
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}
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EXPORT_SYMBOL_GPL(eventfd_signal);
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static void eventfd_free_ctx(struct eventfd_ctx *ctx)
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{
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kfree(ctx);
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}
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static void eventfd_free(struct kref *kref)
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{
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struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
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eventfd_free_ctx(ctx);
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}
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/**
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* eventfd_ctx_get - Acquires a reference to the internal eventfd context.
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* @ctx: [in] Pointer to the eventfd context.
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*
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* Returns: In case of success, returns a pointer to the eventfd context.
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*/
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struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
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{
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kref_get(&ctx->kref);
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return ctx;
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_get);
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/**
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* eventfd_ctx_put - Releases a reference to the internal eventfd context.
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* @ctx: [in] Pointer to eventfd context.
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*
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* The eventfd context reference must have been previously acquired either
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* with eventfd_ctx_get() or eventfd_ctx_fdget().
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*/
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void eventfd_ctx_put(struct eventfd_ctx *ctx)
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{
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kref_put(&ctx->kref, eventfd_free);
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_put);
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static int eventfd_release(struct inode *inode, struct file *file)
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{
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struct eventfd_ctx *ctx = file->private_data;
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wake_up_poll(&ctx->wqh, POLLHUP);
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eventfd_ctx_put(ctx);
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return 0;
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}
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static unsigned int eventfd_poll(struct file *file, poll_table *wait)
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{
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struct eventfd_ctx *ctx = file->private_data;
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unsigned int events = 0;
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unsigned long flags;
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poll_wait(file, &ctx->wqh, wait);
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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if (ctx->count > 0)
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events |= POLLIN;
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if (ctx->count == ULLONG_MAX)
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events |= POLLERR;
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if (ULLONG_MAX - 1 > ctx->count)
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events |= POLLOUT;
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return events;
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}
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static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
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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 64-bit counter value.
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*
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* Returns %0 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 64-bit counter value.
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*
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* Returns %0 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 non-zero.
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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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ssize_t res;
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DECLARE_WAITQUEUE(wait, current);
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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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if (ctx->count > 0)
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res = 0;
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else if (!no_wait) {
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__add_wait_queue(&ctx->wqh, &wait);
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (ctx->count > 0) {
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res = 0;
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break;
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}
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if (signal_pending(current)) {
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res = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(&ctx->wqh.lock);
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schedule();
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spin_lock_irq(&ctx->wqh.lock);
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}
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__remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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}
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if (likely(res == 0)) {
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eventfd_ctx_do_read(ctx, cnt);
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, POLLOUT);
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}
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spin_unlock_irq(&ctx->wqh.lock);
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return res;
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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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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 ucnt;
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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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if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
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return -EFAULT;
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if (ucnt == ULLONG_MAX)
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return -EINVAL;
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spin_lock_irq(&ctx->wqh.lock);
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res = -EAGAIN;
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if (ULLONG_MAX - ctx->count > ucnt)
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res = sizeof(ucnt);
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else if (!(file->f_flags & O_NONBLOCK)) {
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__add_wait_queue(&ctx->wqh, &wait);
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for (res = 0;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (ULLONG_MAX - ctx->count > ucnt) {
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res = sizeof(ucnt);
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break;
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}
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if (signal_pending(current)) {
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res = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(&ctx->wqh.lock);
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schedule();
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spin_lock_irq(&ctx->wqh.lock);
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}
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__remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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}
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if (likely(res > 0)) {
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ctx->count += ucnt;
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, POLLIN);
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}
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spin_unlock_irq(&ctx->wqh.lock);
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return res;
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}
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static const struct file_operations eventfd_fops = {
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.release = eventfd_release,
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.poll = eventfd_poll,
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.read = eventfd_read,
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.write = eventfd_write,
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.llseek = noop_llseek,
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};
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/**
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* eventfd_fget - Acquire a reference of an eventfd file descriptor.
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* @fd: [in] Eventfd file descriptor.
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*
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* Returns a pointer to the eventfd file structure in case of success, or the
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* following error pointer:
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*
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* -EBADF : Invalid @fd file descriptor.
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* -EINVAL : The @fd file descriptor is not an eventfd file.
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*/
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struct file *eventfd_fget(int fd)
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{
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struct file *file;
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file = fget(fd);
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if (!file)
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return ERR_PTR(-EBADF);
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if (file->f_op != &eventfd_fops) {
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fput(file);
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return ERR_PTR(-EINVAL);
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}
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return file;
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}
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EXPORT_SYMBOL_GPL(eventfd_fget);
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/**
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* eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
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* @fd: [in] Eventfd file descriptor.
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*
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* Returns a pointer to the internal eventfd context, otherwise the error
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* pointers returned by the following functions:
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*
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* eventfd_fget
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*/
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struct eventfd_ctx *eventfd_ctx_fdget(int fd)
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{
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struct file *file;
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struct eventfd_ctx *ctx;
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file = eventfd_fget(fd);
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if (IS_ERR(file))
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return (struct eventfd_ctx *) file;
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ctx = eventfd_ctx_get(file->private_data);
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fput(file);
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return ctx;
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
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/**
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* eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
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* @file: [in] Eventfd file pointer.
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*
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* Returns a pointer to the internal eventfd context, otherwise the error
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* pointer:
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*
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* -EINVAL : The @fd file descriptor is not an eventfd file.
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*/
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struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
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{
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if (file->f_op != &eventfd_fops)
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return ERR_PTR(-EINVAL);
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return eventfd_ctx_get(file->private_data);
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}
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EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
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/**
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* eventfd_file_create - Creates an eventfd file pointer.
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* @count: Initial eventfd counter value.
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* @flags: Flags for the eventfd file.
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*
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* This function creates an eventfd file pointer, w/out installing it into
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* the fd table. This is useful when the eventfd file is used during the
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* initialization of data structures that require extra setup after the eventfd
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* creation. So the eventfd creation is split into the file pointer creation
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* phase, and the file descriptor installation phase.
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* In this way races with userspace closing the newly installed file descriptor
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* can be avoided.
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* Returns an eventfd file pointer, or a proper error pointer.
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*/
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struct file *eventfd_file_create(unsigned int count, int flags)
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{
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struct file *file;
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struct eventfd_ctx *ctx;
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/* Check the EFD_* constants for consistency. */
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BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
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BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
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if (flags & ~EFD_FLAGS_SET)
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return ERR_PTR(-EINVAL);
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return ERR_PTR(-ENOMEM);
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kref_init(&ctx->kref);
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init_waitqueue_head(&ctx->wqh);
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ctx->count = count;
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ctx->flags = flags;
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file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
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O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
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if (IS_ERR(file))
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eventfd_free_ctx(ctx);
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return file;
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}
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SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
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{
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int fd, error;
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struct file *file;
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error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
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if (error < 0)
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return error;
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fd = error;
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file = eventfd_file_create(count, flags);
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if (IS_ERR(file)) {
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error = PTR_ERR(file);
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goto err_put_unused_fd;
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}
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fd_install(fd, file);
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return fd;
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err_put_unused_fd:
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put_unused_fd(fd);
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return error;
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}
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SYSCALL_DEFINE1(eventfd, unsigned int, count)
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{
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return sys_eventfd2(count, 0);
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}
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