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/*
* fs/eventfd.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
*
*/
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched/signal.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/anon_inodes.h>
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/kref.h>
#include <linux/eventfd.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
struct eventfd_ctx {
struct kref kref;
wait_queue_head_t wqh;
/*
* Every time that a write(2) is performed on an eventfd, the
* value of the __u64 being written is added to "count" and a
* wakeup is performed on "wqh". A read(2) will return the "count"
* value to userspace, and will reset "count" to zero. The kernel
* side eventfd_signal() also, adds to the "count" counter and
* issue a wakeup.
*/
__u64 count;
unsigned int flags;
};
/**
* eventfd_signal - Adds @n to the eventfd counter.
* @ctx: [in] Pointer to the eventfd context.
* @n: [in] Value of the counter to be added to the eventfd internal counter.
* The value cannot be negative.
*
* This function is supposed to be called by the kernel in paths that do not
* allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
* value, and we signal this as overflow condition by returning a POLLERR
* to poll(2).
*
* Returns the amount by which the counter was incremented. This will be less
* than @n if the counter has overflowed.
*/
__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
{
unsigned long flags;
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ULLONG_MAX - ctx->count < n)
n = ULLONG_MAX - ctx->count;
ctx->count += n;
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLIN);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return n;
}
EXPORT_SYMBOL_GPL(eventfd_signal);
static void eventfd_free_ctx(struct eventfd_ctx *ctx)
{
kfree(ctx);
}
static void eventfd_free(struct kref *kref)
{
struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
eventfd_free_ctx(ctx);
}
/**
* eventfd_ctx_get - Acquires a reference to the internal eventfd context.
* @ctx: [in] Pointer to the eventfd context.
*
* Returns: In case of success, returns a pointer to the eventfd context.
*/
struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
{
kref_get(&ctx->kref);
return ctx;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_get);
/**
* eventfd_ctx_put - Releases a reference to the internal eventfd context.
* @ctx: [in] Pointer to eventfd context.
*
* The eventfd context reference must have been previously acquired either
* with eventfd_ctx_get() or eventfd_ctx_fdget().
*/
void eventfd_ctx_put(struct eventfd_ctx *ctx)
{
kref_put(&ctx->kref, eventfd_free);
}
EXPORT_SYMBOL_GPL(eventfd_ctx_put);
static int eventfd_release(struct inode *inode, struct file *file)
{
struct eventfd_ctx *ctx = file->private_data;
wake_up_poll(&ctx->wqh, POLLHUP);
eventfd_ctx_put(ctx);
return 0;
}
static unsigned int eventfd_poll(struct file *file, poll_table *wait)
{
struct eventfd_ctx *ctx = file->private_data;
unsigned int events = 0;
u64 count;
poll_wait(file, &ctx->wqh, wait);
/*
* All writes to ctx->count occur within ctx->wqh.lock. This read
* can be done outside ctx->wqh.lock because we know that poll_wait
* takes that lock (through add_wait_queue) if our caller will sleep.
*
* The read _can_ therefore seep into add_wait_queue's critical
* section, but cannot move above it! add_wait_queue's spin_lock acts
* as an acquire barrier and ensures that the read be ordered properly
* against the writes. The following CAN happen and is safe:
*
* poll write
* ----------------- ------------
* lock ctx->wqh.lock (in poll_wait)
* count = ctx->count
* __add_wait_queue
* unlock ctx->wqh.lock
* lock ctx->qwh.lock
* ctx->count += n
* if (waitqueue_active)
* wake_up_locked_poll
* unlock ctx->qwh.lock
* eventfd_poll returns 0
*
* but the following, which would miss a wakeup, cannot happen:
*
* poll write
* ----------------- ------------
* count = ctx->count (INVALID!)
* lock ctx->qwh.lock
* ctx->count += n
* **waitqueue_active is false**
* **no wake_up_locked_poll!**
* unlock ctx->qwh.lock
* lock ctx->wqh.lock (in poll_wait)
* __add_wait_queue
* unlock ctx->wqh.lock
* eventfd_poll returns 0
*/
count = READ_ONCE(ctx->count);
if (count > 0)
events |= POLLIN;
if (count == ULLONG_MAX)
events |= POLLERR;
if (ULLONG_MAX - 1 > count)
events |= POLLOUT;
return events;
}
static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
{
*cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
ctx->count -= *cnt;
}
/**
* eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
* @ctx: [in] Pointer to eventfd context.
* @wait: [in] Wait queue to be removed.
* @cnt: [out] Pointer to the 64-bit counter value.
*
* Returns %0 if successful, or the following error codes:
*
* -EAGAIN : The operation would have blocked.
*
* This is used to atomically remove a wait queue entry from the eventfd wait
* queue head, and read/reset the counter value.
*/
int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
__u64 *cnt)
{
unsigned long flags;
spin_lock_irqsave(&ctx->wqh.lock, flags);
eventfd_ctx_do_read(ctx, cnt);
__remove_wait_queue(&ctx->wqh, wait);
if (*cnt != 0 && waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLOUT);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return *cnt != 0 ? 0 : -EAGAIN;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
/**
* eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
* @ctx: [in] Pointer to eventfd context.
* @no_wait: [in] Different from zero if the operation should not block.
* @cnt: [out] Pointer to the 64-bit counter value.
*
* Returns %0 if successful, or the following error codes:
*
* -EAGAIN : The operation would have blocked but @no_wait was non-zero.
* -ERESTARTSYS : A signal interrupted the wait operation.
*
* If @no_wait is zero, the function might sleep until the eventfd internal
* counter becomes greater than zero.
*/
ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
{
ssize_t res;
DECLARE_WAITQUEUE(wait, current);
spin_lock_irq(&ctx->wqh.lock);
*cnt = 0;
res = -EAGAIN;
if (ctx->count > 0)
res = 0;
else if (!no_wait) {
__add_wait_queue(&ctx->wqh, &wait);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
if (ctx->count > 0) {
res = 0;
break;
}
if (signal_pending(current)) {
res = -ERESTARTSYS;
break;
}
spin_unlock_irq(&ctx->wqh.lock);
schedule();
spin_lock_irq(&ctx->wqh.lock);
}
__remove_wait_queue(&ctx->wqh, &wait);
__set_current_state(TASK_RUNNING);
}
if (likely(res == 0)) {
eventfd_ctx_do_read(ctx, cnt);
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, POLLOUT);
}
spin_unlock_irq(&ctx->wqh.lock);
return res;
}
EXPORT_SYMBOL_GPL(eventfd_ctx_read);
static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct eventfd_ctx *ctx = file->private_data;
ssize_t res;
__u64 cnt;
if (count < sizeof(cnt))
return -EINVAL;
res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
if (res < 0)
return res;
return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
}
static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
loff_t *ppos)
{
struct eventfd_ctx *ctx = file->private_data;
ssize_t res;
__u64 ucnt;
DECLARE_WAITQUEUE(wait, current);
if (count < sizeof(ucnt))
return -EINVAL;
if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
return -EFAULT;
if (ucnt == ULLONG_MAX)
return -EINVAL;
spin_lock_irq(&ctx
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