1 files changed, 349 insertions, 0 deletions
diff --git a/fs/signalfd.c b/fs/signalfd.c
new file mode 100644
index 000000000000..7cfeab412b45
--- /dev/null
+++ b/fs/signalfd.c
@@ -0,0 +1,349 @@
+/*
+ *  fs/signalfd.c
+ *
+ *  Copyright (C) 2003  Linus Torvalds
+ *
+ *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
+ *      Changed ->read() to return a siginfo strcture instead of signal number.
+ *      Fixed locking in ->poll().
+ *      Added sighand-detach notification.
+ *      Added fd re-use in sys_signalfd() syscall.
+ *      Now using anonymous inode source.
+ *      Thanks to Oleg Nesterov for useful code review and suggestions.
+ *      More comments and suggestions from Arnd Bergmann.
+ */
+
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/signal.h>
+#include <linux/list.h>
+#include <linux/anon_inodes.h>
+#include <linux/signalfd.h>
+
+struct signalfd_ctx {
+	struct list_head lnk;
+	wait_queue_head_t wqh;
+	sigset_t sigmask;
+	struct task_struct *tsk;
+};
+
+struct signalfd_lockctx {
+	struct task_struct *tsk;
+	unsigned long flags;
+};
+
+/*
+ * Tries to acquire the sighand lock. We do not increment the sighand
+ * use count, and we do not even pin the task struct, so we need to
+ * do it inside an RCU read lock, and we must be prepared for the
+ * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
+ * being detached. We return 0 if the sighand has been detached, or
+ * 1 if we were able to pin the sighand lock.
+ */
+static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
+{
+	struct sighand_struct *sighand = NULL;
+
+	rcu_read_lock();
+	lk->tsk = rcu_dereference(ctx->tsk);
+	if (likely(lk->tsk != NULL))
+		sighand = lock_task_sighand(lk->tsk, &lk->flags);
+	rcu_read_unlock();
+
+	if (sighand && !ctx->tsk) {
+		unlock_task_sighand(lk->tsk, &lk->flags);
+		sighand = NULL;
+	}
+
+	return sighand != NULL;
+}
+
+static void signalfd_unlock(struct signalfd_lockctx *lk)
+{
+	unlock_task_sighand(lk->tsk, &lk->flags);
+}
+
+/*
+ * This must be called with the sighand lock held.
+ */
+void signalfd_deliver(struct task_struct *tsk, int sig)
+{
+	struct sighand_struct *sighand = tsk->sighand;
+	struct signalfd_ctx *ctx, *tmp;
+
+	BUG_ON(!sig);
+	list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
+		/*
+		 * We use a negative signal value as a way to broadcast that the
+		 * sighand has been orphaned, so that we can notify all the
+		 * listeners about this. Remember the ctx->sigmask is inverted,
+		 * so if the user is interested in a signal, that corresponding
+		 * bit will be zero.
+		 */
+		if (sig < 0) {
+			if (ctx->tsk == tsk) {
+				ctx->tsk = NULL;
+				list_del_init(&ctx->lnk);
+				wake_up(&ctx->wqh);
+			}
+		} else {
+			if (!sigismember(&ctx->sigmask, sig))
+				wake_up(&ctx->wqh);
+		}
+	}
+}
+
+static void signalfd_cleanup(struct signalfd_ctx *ctx)
+{
+	struct signalfd_lockctx lk;
+
+	/*
+	 * This is tricky. If the sighand is gone, we do not need to remove
+	 * context from the list, the list itself won't be there anymore.
+	 */
+	if (signalfd_lock(ctx, &lk)) {
+		list_del(&ctx->lnk);
+		signalfd_unlock(&lk);
+	}
+	kfree(ctx);
+}
+
+static int signalfd_release(struct inode *inode, struct file *file)
+{
+	signalfd_cleanup(file->private_data);
+	return 0;
+}
+
+static unsigned int signalfd_poll(struct file *file, poll_table *wait)
+{
+	struct signalfd_ctx *ctx = file->private_data;
+	unsigned int events = 0;
+	struct signalfd_lockctx lk;
+
+	poll_wait(file, &ctx->wqh, wait);
+
+	/*
+	 * Let the caller get a POLLIN in this case, ala socket recv() when
+	 * the peer disconnects.
+	 */
+	if (signalfd_lock(ctx, &lk)) {
+		if (next_signal(&lk.tsk->pending, &ctx->sigmask) > 0 ||
+		    next_signal(&lk.tsk->signal->shared_pending,
+				&ctx->sigmask) > 0)
+			events |= POLLIN;
+		signalfd_unlock(&lk);
+	} else
+		events |= POLLIN;
+
+	return events;
+}
+
+/*
+ * Copied from copy_siginfo_to_user() in kernel/signal.c
+ */
+static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
+			     siginfo_t const *kinfo)
+{
+	long err;
+
+	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
+
+	/*
+	 * Unused memebers should be zero ...
+	 */
+	err = __clear_user(uinfo, sizeof(*uinfo));
+
+	/*
+	 * If you change siginfo_t structure, please be sure
+	 * this code is fixed accordingly.
+	 */
+	err |= __put_user(kinfo->si_signo, &uinfo->signo);
+	err |= __put_user(kinfo->si_errno, &uinfo->err);
+	err |= __put_user((short)kinfo->si_code, &uinfo->code);
+	switch (kinfo->si_code & __SI_MASK) {
+	case __SI_KILL:
+		err |= __put_user(kinfo->si_pid, &uinfo->pid);
+		err |= __put_user(kinfo->si_uid, &uinfo->uid);
+		break;
+	case __SI_TIMER:
+		 err |= __put_user(kinfo->si_tid, &uinfo->tid);
+		 err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
+		 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
+		break;
+	case __SI_POLL:
+		err |= __put_user(kinfo->si_band, &uinfo->band);
+		err |= __put_user(kinfo->si_fd, &uinfo->fd);
+		break;
+	case __SI_FAULT:
+		err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
+#ifdef __ARCH_SI_TRAPNO
+		err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
+#endif
+		break;
+	case __SI_CHLD:
+		err |= __put_user(kinfo->si_pid, &uinfo->pid);
+		err |= __put_user(kinfo->si_uid, &uinfo->uid);
+		err |= __put_user(kinfo->si_status, &uinfo->status);
+		err |= __put_user(kinfo->si_utime, &uinfo->utime);
+		err |= __put_user(kinfo->si_stime, &uinfo->stime);
+		break;
+	case __SI_RT: /* This is not generated by the kernel as of now. */
+	case __SI_MESGQ: /* But this is */
+		err |= __put_user(kinfo->si_pid, &uinfo->pid);
+		err |= __put_user(kinfo->si_uid, &uinfo->uid);
+		err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
+		break;
+	default: /* this is just in case for now ... */
+		err |= __put_user(kinfo->si_pid, &uinfo->pid);
+		err |= __put_user(kinfo->si_uid, &uinfo->uid);
+		break;
+	}
+
+	return err ? -EFAULT: sizeof(*uinfo);
+}
+
+/*
+ * Returns either the size of a "struct signalfd_siginfo", or zero if the
+ * sighand we are attached to, has been orphaned. The "count" parameter
+ * must be at least the size of a "struct signalfd_siginfo".
+ */
+static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
+			     loff_t *ppos)
+{
+	struct signalfd_ctx *ctx = file->private_data;
+	ssize_t res = 0;
+	int locked, signo;
+	siginfo_t info;
+	struct signalfd_lockctx lk;
+	DECLARE_WAITQUEUE(wait, current);
+
+	if (count < sizeof(struct signalfd_siginfo))
+		return -EINVAL;
+	locked = signalfd_lock(ctx, &lk);
+	if (!locked)
+		return 0;
+	res = -EAGAIN;
+	signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
+	if (signo == 0 && !(file->f_flags & O_NONBLOCK)) {
+		add_wait_queue(&ctx->wqh, &wait);
+		for (;;) {
+			set_current_state(TASK_INTERRUPTIBLE);
+			signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
+			if (signo != 0)
+				break;
+			if (signal_pending(current)) {
+				res = -ERESTARTSYS;
+				break;
+			}
+			signalfd_unlock(&lk);
+			schedule();
+			locked = signalfd_lock(ctx, &lk);
+			if (unlikely(!locked)) {
+				/*
+				 * Let the caller read zero byte, ala socket
+				 * recv() when the peer disconnect. This test
+				 * must be done before doing a dequeue_signal(),
+				 * because if the sighand has been orphaned,
+				 * the dequeue_signal() call is going to crash.
+				 */
+				res = 0;
+				break;
+			}
+		}
+		remove_wait_queue(&ctx->wqh, &wait);
+		__set_current_state(TASK_RUNNING);
+	}
+	if (likely(locked))
+		signalfd_unlock(&lk);
+	if (likely(signo))
+		res = signalfd_copyinfo((struct signalfd_siginfo __user *) buf,
+					&info);
+
+	return res;
+}
+
+static const struct file_operations signalfd_fops = {
+	.release	= signalfd_release,
+	.poll		= signalfd_poll,
+	.read		= signalfd_read,
+};
+
+/*
+ * Create a file descriptor that is associated with our signal
+ * state. We can pass it around to others if we want to, but
+ * it will always be _our_ signal state.
+ */
+asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
+{
+	int error;
+	sigset_t sigmask;
+	struct signalfd_ctx *ctx;
+	struct sighand_struct *sighand;
+	struct file *file;
+	struct inode *inode;
+	struct signalfd_lockctx lk;
+
+	if (sizemask != sizeof(sigset_t) ||
+	    copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
+		return error = -EINVAL;
+	sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
+	signotset(&sigmask);
+
+	if (ufd == -1) {
+		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+		if (!ctx)
+			return -ENOMEM;
+
+		init_waitqueue_head(&ctx->wqh);
+		ctx->sigmask = sigmask;
+		ctx->tsk = current;
+
+		sighand = current->sighand;
+		/*
+		 * Add this fd to the list of signal listeners.
+		 */
+		spin_lock_irq(&sighand->siglock);
+		list_add_tail(&ctx->lnk, &sighand->signalfd_list);
+		spin_unlock_irq(&sighand->siglock);
+
+		/*
+		 * When we call this, the initialization must be complete, since
+		 * anon_inode_getfd() will install the fd.
+		 */
+		error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
+					 &signalfd_fops, ctx);
+		if (error)
+			goto err_fdalloc;
+	} else {
+		file = fget(ufd);
+		if (!file)
+			return -EBADF;
+		ctx = file->private_data;
+		if (file->f_op != &signalfd_fops) {
+			fput(file);
+			return -EINVAL;
+		}
+		/*
+		 * We need to be prepared of the fact that the sighand this fd
+		 * is attached to, has been detched. In that case signalfd_lock()
+		 * will return 0, and we'll just skip setting the new mask.
+		 */
+		if (signalfd_lock(ctx, &lk)) {
+			ctx->sigmask = sigmask;
+			signalfd_unlock(&lk);
+		}
+		wake_up(&ctx->wqh);
+		fput(file);
+	}
+
+	return ufd;
+
+err_fdalloc:
+	signalfd_cleanup(ctx);
+	return error;
+}
+