Hi,
Gathering signals in bulk enables server applications to drain a signal
queue (almost full of realtime signals) more efficiently by reducing the
syscall and file look-up overhead.
Very similar to the sigtimedwait4() call described by Niels Provos,
Chuck Lever, and Stephen Tweedie in a paper entitled "Analyzing the
Overload Behavior of a Simple Web Server". The paper lists more details
and advantages.
Signed-off-by: Davi E. M. Arnaut <[email protected]>
diff --git a/fs/signalfd.c b/fs/signalfd.c
index 7cfeab4..f6303c5 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -11,6 +11,8 @@
* Now using anonymous inode source.
* Thanks to Oleg Nesterov for useful code review and suggestions.
* More comments and suggestions from Arnd Bergmann.
+ * Sat May 19, 2007: Davi E. M. Arnaut <[email protected]>
+ * Retrieve multiple signals with one read() call
*/
#include <linux/file.h>
@@ -206,6 +208,64 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
return err ? -EFAULT: sizeof(*uinfo);
}
+static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
+ int nonblock)
+{
+ int locked;
+ ssize_t ret;
+ struct signalfd_lockctx lk;
+ DECLARE_WAITQUEUE(wait, current);
+
+ locked = signalfd_lock(ctx, &lk);
+ if (!locked)
+ return 0;
+
+ ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
+ switch (ret) {
+ case 0:
+ if (!nonblock)
+ break;
+ ret = -EAGAIN;
+ default:
+ signalfd_unlock(&lk);
+ return ret;
+ }
+
+ add_wait_queue(&ctx->wqh, &wait);
+ for (;;) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
+ if (ret != 0)
+ break;
+ if (signal_pending(current)) {
+ ret = -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.
+ */
+ ret = 0;
+ break;
+ }
+ }
+
+ remove_wait_queue(&ctx->wqh, &wait);
+ __set_current_state(TASK_RUNNING);
+
+ if (likely(locked))
+ signalfd_unlock(&lk);
+
+ return ret;
+}
+
/*
* Returns either the size of a "struct signalfd_siginfo", or zero if the
* sighand we are attached to, has been orphaned. The "count" parameter
@@ -215,55 +275,30 @@ 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;
+ struct signalfd_siginfo __user *siginfo;
+ int nonblock = file->f_flags & O_NONBLOCK;
+ ssize_t ret, total = 0;
siginfo_t info;
- struct signalfd_lockctx lk;
- DECLARE_WAITQUEUE(wait, current);
- if (count < sizeof(struct signalfd_siginfo))
+ count /= sizeof(struct signalfd_siginfo);
+ if (!count)
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;
+ siginfo = (struct signalfd_siginfo __user *) buf;
+
+ do {
+ ret = signalfd_dequeue(ctx, &info, nonblock);
+ if (unlikely(ret <= 0))
+ break;
+ ret = signalfd_copyinfo(siginfo, &info);
+ if (ret < 0)
+ break;
+ siginfo++;
+ total += ret;
+ nonblock = 1;
+ } while (--count);
+
+ return total ? total : ret;
}
static const struct file_operations signalfd_fops = {
-
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