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458 lines
12 KiB
458 lines
12 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* fs/eventfd.c |
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* |
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* Copyright (C) 2007 Davide Libenzi <[email protected]> |
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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/signal.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/export.h> |
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#include <linux/kref.h> |
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#include <linux/eventfd.h> |
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#include <linux/proc_fs.h> |
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#include <linux/seq_file.h> |
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#include <linux/idr.h> |
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#include <linux/uio.h> |
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static DEFINE_IDA(eventfd_ida); |
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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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int id; |
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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 returning a EPOLLERR |
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* to poll(2). |
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* |
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* Returns the amount by which the counter was incremented. This will be less |
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* than @n if the counter has overflowed. |
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*/ |
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__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) |
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{ |
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unsigned long flags; |
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/* |
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* Deadlock or stack overflow issues can happen if we recurse here |
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* through waitqueue wakeup handlers. If the caller users potentially |
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* nested waitqueues with custom wakeup handlers, then it should |
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* check eventfd_signal_allowed() before calling this function. If |
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* it returns false, the eventfd_signal() call should be deferred to a |
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* safe context. |
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*/ |
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if (WARN_ON_ONCE(current->in_eventfd_signal)) |
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return 0; |
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spin_lock_irqsave(&ctx->wqh.lock, flags); |
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current->in_eventfd_signal = 1; |
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if (ULLONG_MAX - ctx->count < n) |
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n = 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, EPOLLIN); |
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current->in_eventfd_signal = 0; |
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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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if (ctx->id >= 0) |
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ida_simple_remove(&eventfd_ida, ctx->id); |
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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_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_fdget() or eventfd_ctx_fileget(). |
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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, EPOLLHUP); |
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eventfd_ctx_put(ctx); |
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return 0; |
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} |
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static __poll_t 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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__poll_t events = 0; |
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u64 count; |
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poll_wait(file, &ctx->wqh, wait); |
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/* |
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* All writes to ctx->count occur within ctx->wqh.lock. This read |
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* can be done outside ctx->wqh.lock because we know that poll_wait |
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* takes that lock (through add_wait_queue) if our caller will sleep. |
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* |
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* The read _can_ therefore seep into add_wait_queue's critical |
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* section, but cannot move above it! add_wait_queue's spin_lock acts |
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* as an acquire barrier and ensures that the read be ordered properly |
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* against the writes. The following CAN happen and is safe: |
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* |
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* poll write |
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* ----------------- ------------ |
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* lock ctx->wqh.lock (in poll_wait) |
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* count = ctx->count |
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* __add_wait_queue |
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* unlock ctx->wqh.lock |
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* lock ctx->qwh.lock |
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* ctx->count += n |
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* if (waitqueue_active) |
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* wake_up_locked_poll |
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* unlock ctx->qwh.lock |
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* eventfd_poll returns 0 |
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* |
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* but the following, which would miss a wakeup, cannot happen: |
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* |
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* poll write |
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* ----------------- ------------ |
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* count = ctx->count (INVALID!) |
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* lock ctx->qwh.lock |
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* ctx->count += n |
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* **waitqueue_active is false** |
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* **no wake_up_locked_poll!** |
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* unlock ctx->qwh.lock |
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* lock ctx->wqh.lock (in poll_wait) |
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* __add_wait_queue |
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* unlock ctx->wqh.lock |
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* eventfd_poll returns 0 |
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*/ |
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count = READ_ONCE(ctx->count); |
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if (count > 0) |
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events |= EPOLLIN; |
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if (count == ULLONG_MAX) |
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events |= EPOLLERR; |
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if (ULLONG_MAX - 1 > count) |
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events |= EPOLLOUT; |
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return events; |
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} |
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void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt) |
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{ |
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lockdep_assert_held(&ctx->wqh.lock); |
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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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EXPORT_SYMBOL_GPL(eventfd_ctx_do_read); |
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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_entry_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, EPOLLOUT); |
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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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static ssize_t eventfd_read(struct kiocb *iocb, struct iov_iter *to) |
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{ |
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struct file *file = iocb->ki_filp; |
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struct eventfd_ctx *ctx = file->private_data; |
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__u64 ucnt = 0; |
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DECLARE_WAITQUEUE(wait, current); |
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if (iov_iter_count(to) < sizeof(ucnt)) |
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return -EINVAL; |
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spin_lock_irq(&ctx->wqh.lock); |
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if (!ctx->count) { |
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if ((file->f_flags & O_NONBLOCK) || |
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(iocb->ki_flags & IOCB_NOWAIT)) { |
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spin_unlock_irq(&ctx->wqh.lock); |
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return -EAGAIN; |
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} |
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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) |
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break; |
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if (signal_pending(current)) { |
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__remove_wait_queue(&ctx->wqh, &wait); |
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__set_current_state(TASK_RUNNING); |
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spin_unlock_irq(&ctx->wqh.lock); |
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return -ERESTARTSYS; |
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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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eventfd_ctx_do_read(ctx, &ucnt); |
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if (waitqueue_active(&ctx->wqh)) |
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wake_up_locked_poll(&ctx->wqh, EPOLLOUT); |
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spin_unlock_irq(&ctx->wqh.lock); |
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if (unlikely(copy_to_iter(&ucnt, sizeof(ucnt), to) != sizeof(ucnt))) |
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return -EFAULT; |
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return sizeof(ucnt); |
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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, EPOLLIN); |
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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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#ifdef CONFIG_PROC_FS |
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static void eventfd_show_fdinfo(struct seq_file *m, struct file *f) |
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{ |
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struct eventfd_ctx *ctx = f->private_data; |
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spin_lock_irq(&ctx->wqh.lock); |
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seq_printf(m, "eventfd-count: %16llx\n", |
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(unsigned long long)ctx->count); |
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spin_unlock_irq(&ctx->wqh.lock); |
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seq_printf(m, "eventfd-id: %d\n", ctx->id); |
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} |
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#endif |
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static const struct file_operations eventfd_fops = { |
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#ifdef CONFIG_PROC_FS |
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.show_fdinfo = eventfd_show_fdinfo, |
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#endif |
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.release = eventfd_release, |
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.poll = eventfd_poll, |
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.read_iter = 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 eventfd_ctx *ctx; |
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struct fd f = fdget(fd); |
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if (!f.file) |
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return ERR_PTR(-EBADF); |
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ctx = eventfd_ctx_fileget(f.file); |
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fdput(f); |
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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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struct eventfd_ctx *ctx; |
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if (file->f_op != &eventfd_fops) |
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return ERR_PTR(-EINVAL); |
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ctx = file->private_data; |
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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_fileget); |
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static int do_eventfd(unsigned int count, int flags) |
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{ |
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struct eventfd_ctx *ctx; |
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struct file *file; |
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int fd; |
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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 -EINVAL; |
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); |
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if (!ctx) |
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return -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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ctx->id = ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL); |
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flags &= EFD_SHARED_FCNTL_FLAGS; |
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flags |= O_RDWR; |
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fd = get_unused_fd_flags(flags); |
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if (fd < 0) |
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goto err; |
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file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags); |
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if (IS_ERR(file)) { |
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put_unused_fd(fd); |
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fd = PTR_ERR(file); |
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goto err; |
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} |
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file->f_mode |= FMODE_NOWAIT; |
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fd_install(fd, file); |
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return fd; |
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err: |
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eventfd_free_ctx(ctx); |
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return fd; |
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} |
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SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags) |
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{ |
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return do_eventfd(count, flags); |
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} |
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SYSCALL_DEFINE1(eventfd, unsigned int, count) |
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{ |
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return do_eventfd(count, 0); |
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} |
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