[PATCH-RFC 1/2] eventfd: reorganize the code to simplify new flags

Michael S. Tsirkin
2009-07-28T17:55:50Z

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

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
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 +34,37 @@ 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 (eventfd_writeable(ctx, 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