[PATCHv2] eventfd: reorganize the code slightly

["Michael S. Tsirkin" <mst@redhat.com>]

This slightly reorganizes the code in eventfd, encapsulating counter
math in inline functions, so that it will be easier to follow the logic
and to add new flags.
No functional changes.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Changes from v1:
move a bugfix from EFD_STATE patch to this patch
noted by Paolo Bonzini

 fs/eventfd.c |   56 ++++++++++++++++++++++++++++++++++++++++++--------------
 1 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 31d12de..347a0e0 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -34,6 +34,36 @@ struct eventfd_ctx {
 	unsigned int flags;
 };
 
+static inline int eventfd_readable(struct eventfd_ctx *ctx)
+{
+	return ctx->count > 0;
+}
+
+static inline int eventfd_writeable(struct eventfd_ctx *ctx, u64 n)
+{
+	return ULLONG_MAX - n > ctx->count;
+}
+
+static inline int eventfd_overflow(struct eventfd_ctx *ctx, u64 cnt)
+{
+	return cnt == ULLONG_MAX;
+}
+
+static inline void eventfd_dowrite(struct eventfd_ctx *ctx, u64 ucnt)
+{
+	if (ULLONG_MAX - ctx->count < ucnt)
+		ucnt = ULLONG_MAX - ctx->count;
+
+	ctx->count += ucnt;
+}
+
+static inline u64 eventfd_doread(struct eventfd_ctx *ctx)
+{
+	u64 ucnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
+	ctx->count -= ucnt;
+	return ucnt;
+}
+
 /**
  * eventfd_signal - Adds @n to the eventfd counter.
  * @ctx: [in] Pointer to the eventfd context.
@@ -57,9 +88,7 @@ int eventfd_signal(struct eventfd_ctx *ctx, int n)
 	if (n < 0)
 		return -EINVAL;
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
-	if (ULLONG_MAX - ctx->count < n)
-		n = (int) (ULLONG_MAX - ctx->count);
-	ctx->count += n;
+	eventfd_dowrite(ctx, n);
 	if (waitqueue_active(&ctx->wqh))
 		wake_up_locked_poll(&ctx->wqh, POLLIN);
 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
@@ -119,11 +148,11 @@ static unsigned int eventfd_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &ctx->wqh, wait);
 
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
-	if (ctx->count > 0)
+	if (eventfd_readable(ctx))
 		events |= POLLIN;
-	if (ctx->count == ULLONG_MAX)
+	if (eventfd_overflow(ctx, ctx->count))
 		events |= POLLERR;
-	if (ULLONG_MAX - 1 > ctx->count)
+	if (eventfd_writeable(ctx, 1))
 		events |= POLLOUT;
 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 
@@ -142,13 +171,13 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
 		return -EINVAL;
 	spin_lock_irq(&ctx->wqh.lock);
 	res = -EAGAIN;
-	if (ctx->count > 0)
+	if (eventfd_readable(ctx))
 		res = sizeof(ucnt);
 	else if (!(file->f_flags & O_NONBLOCK)) {
 		__add_wait_queue(&ctx->wqh, &wait);
 		for (res = 0;;) {
 			set_current_state(TASK_INTERRUPTIBLE);
-			if (ctx->count > 0) {
+			if (eventfd_readable(ctx)) {
 				res = sizeof(ucnt);
 				break;
 			}
@@ -164,8 +193,7 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
 		__set_current_state(TASK_RUNNING);
 	}
 	if (likely(res > 0)) {
-		ucnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
-		ctx->count -= ucnt;
+		ucnt = eventfd_doread(ctx);
 		if (waitqueue_active(&ctx->wqh))
 			wake_up_locked_poll(&ctx->wqh, POLLOUT);
 	}
@@ -188,17 +216,17 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
 		return -EINVAL;
 	if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
 		return -EFAULT;
-	if (ucnt == ULLONG_MAX)
+	if (eventfd_overflow(ctx, ucnt))
 		return -EINVAL;
 	spin_lock_irq(&ctx->wqh.lock);
 	res = -EAGAIN;
-	if (ULLONG_MAX - ctx->count > ucnt)
+	if (eventfd_writeable(ctx, ucnt))
 		res = sizeof(ucnt);
 	else if (!(file->f_flags & O_NONBLOCK)) {
 		__add_wait_queue(&ctx->wqh, &wait);
 		for (res = 0;;) {
 			set_current_state(TASK_INTERRUPTIBLE);
-			if (ULLONG_MAX - ctx->count > ucnt) {
+			if (eventfd_writeable(ctx, ucnt)) {
 				res = sizeof(ucnt);
 				break;
 			}
@@ -214,7 +242,7 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
 		__set_current_state(TASK_RUNNING);
 	}
 	if (likely(res > 0)) {
-		ctx->count += ucnt;
+		eventfd_dowrite(ctx, ucnt);
 		if (waitqueue_active(&ctx->wqh))
 			wake_up_locked_poll(&ctx->wqh, POLLIN);
 	}
-- 
1.6.2.5