linux-imx
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static int eventfd_release(struct inode *inode, struct file *file){ struct eventfd_ctx *ctx = file->private_data; wake_up_poll(&ctx->wqh, EPOLLHUP); eventfd_ctx_put(ctx); return 0;}static struct wait_queue_head *eventfd_get_poll_head(struct file *file, __poll_t events){ struct eventfd_ctx *ctx = file->private_data; return &ctx->wqh;}static __poll_t eventfd_poll_mask(struct file *file, __poll_t eventmask)static __poll_t eventfd_poll(struct file *file, poll_table *wait){ struct eventfd_ctx *ctx = file->private_data; __poll_t 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: * * **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 |= (EPOLLIN & eventmask); events |= EPOLLIN; if (count == ULLONG_MAX) events |= EPOLLERR; if (ULLONG_MAX - 1 > count) events |= (EPOLLOUT & eventmask); events |= EPOLLOUT; 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;} (unsigned long long)ctx->count); spin_unlock_irq(&ctx->wqh.lock);}#endifstatic const struct file_operations eventfd_fops = {#ifdef CONFIG_PROC_FS .show_fdinfo = eventfd_show_fdinfo,#endif .release = eventfd_release, .get_poll_head = eventfd_get_poll_head, .poll_mask = eventfd_poll_mask, .poll = eventfd_poll, .read = eventfd_read, .write = eventfd_write, .llseek = noop_llseek,};/** * eventfd_fget - Acquire a reference of an eventfd file descriptor. * @fd: [in] Eventfd file descriptor. * * Returns a pointer to the eventfd file structure in case of success, or the