[PATCH] eventfd: change int to __u64 in eventfd_signal()

[PATCH] eventfd: change int to __u64 in eventfd_signal()

[handai.szj]

From: Sha Zhengju <handai.szj@taobao.com>

From: Sha Zhengju <handai.szj@taobao.com>

eventfd_ctx->count is an __u64 counter which is allowed to reach ULLONG_MAX.
Now eventfd_write() add an __u64 value to "count", but kernel side 
eventfd_signal() only add an int value to it. So make them consistent here.  

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>

---
 fs/eventfd.c            |    4 ++--
 include/linux/eventfd.h |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/eventfd.c b/fs/eventfd.c
index dba15fe..9e63e42 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -51,7 +51,7 @@ struct eventfd_ctx {
  *
  * -EINVAL    : The value of @n is negative.
  */
-int eventfd_signal(struct eventfd_ctx *ctx, int n)
+__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
 {
 	unsigned long flags;
 
@@ -59,7 +59,7 @@ int eventfd_signal(struct eventfd_ctx *ctx, int n)
 		return -EINVAL;
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
 	if (ULLONG_MAX - ctx->count < n)
-		n = (int) (ULLONG_MAX - ctx->count);
+		n = ULLONG_MAX - ctx->count;
 	ctx->count += n;
 	if (waitqueue_active(&ctx->wqh))
 		wake_up_locked_poll(&ctx->wqh, POLLIN);
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index 91bb4f2..3c3ef19 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -34,7 +34,7 @@ void eventfd_ctx_put(struct eventfd_ctx *ctx);
 struct file *eventfd_fget(int fd);
 struct eventfd_ctx *eventfd_ctx_fdget(int fd);
 struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
-int eventfd_signal(struct eventfd_ctx *ctx, int n);
+__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n);
 ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt);
 int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
 				  __u64 *cnt);
-- 
1.7.4.1

Re: [PATCH] eventfd: change int to __u64 in eventfd_signal()

[Andrew Morton]

On Thu, 12 Apr 2012 18:01:20 +0800
handai.szj@gmail.com wrote:

> From: Sha Zhengju <handai.szj@taobao.com>
> 
> From: Sha Zhengju <handai.szj@taobao.com>
> 
> eventfd_ctx->count is an __u64 counter which is allowed to reach ULLONG_MAX.
> Now eventfd_write() add an __u64 value to "count", but kernel side 
> eventfd_signal() only add an int value to it. So make them consistent here.  
> 
> ...
>
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -51,7 +51,7 @@ struct eventfd_ctx {
>   *
>   * -EINVAL    : The value of @n is negative.
>   */
> -int eventfd_signal(struct eventfd_ctx *ctx, int n)
> +__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
>  {
>  	unsigned long flags;
>  
> @@ -59,7 +59,7 @@ int eventfd_signal(struct eventfd_ctx *ctx, int n)
>  		return -EINVAL;
>  	spin_lock_irqsave(&ctx->wqh.lock, flags);
>  	if (ULLONG_MAX - ctx->count < n)
> -		n = (int) (ULLONG_MAX - ctx->count);
> +		n = ULLONG_MAX - ctx->count;
>  	ctx->count += n;
>  	if (waitqueue_active(&ctx->wqh))
>  		wake_up_locked_poll(&ctx->wqh, POLLIN);

Changing `n' to an unsigned type makes the "if (n < 0)" test a no-op.

Every in-kernel caller of eventfd_signal() passes n=1.  All of them. 
Perhaps we can just remove that argument and hard-wire the +1
assumption into eventfd_signal().

Re: [PATCH] eventfd: change int to __u64 in eventfd_signal()

[Sha Zhengju]

On 04/13/2012 07:09 AM, Andrew Morton wrote:
> On Thu, 12 Apr 2012 18:01:20 +0800
> handai.szj@gmail.com wrote:
>
>> From: Sha Zhengju<handai.szj@taobao.com>
>>
>> From: Sha Zhengju<handai.szj@taobao.com>
>>
>> eventfd_ctx->count is an __u64 counter which is allowed to reach ULLONG_MAX.
>> Now eventfd_write() add an __u64 value to "count", but kernel side
>> eventfd_signal() only add an int value to it. So make them consistent here.
>>
>> ...
>>
>> --- a/fs/eventfd.c
>> +++ b/fs/eventfd.c
>> @@ -51,7 +51,7 @@ struct eventfd_ctx {
>>    *
>>    * -EINVAL    : The value of @n is negative.
>>    */
>> -int eventfd_signal(struct eventfd_ctx *ctx, int n)
>> +__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
>>   {
>>   	unsigned long flags;
>>
>> @@ -59,7 +59,7 @@ int eventfd_signal(struct eventfd_ctx *ctx, int n)
>>   		return -EINVAL;
>>   	spin_lock_irqsave(&ctx->wqh.lock, flags);
>>   	if (ULLONG_MAX - ctx->count<  n)
>> -		n = (int) (ULLONG_MAX - ctx->count);
>> +		n = ULLONG_MAX - ctx->count;
>>   	ctx->count += n;
>>   	if (waitqueue_active(&ctx->wqh))
>>   		wake_up_locked_poll(&ctx->wqh, POLLIN);
> Changing `n' to an unsigned type makes the "if (n<  0)" test a no-op.
>
yeah, it's really not necessary. I slipped up..
> Every in-kernel caller of eventfd_signal() passes n=1.  All of them.
> Perhaps we can just remove that argument and hard-wire the +1
> assumption into eventfd_signal().
A userspace write(2) performing on an eventfd can pass an u64 value to
"count" and issue a wakeup, I think the kernel side can just be in 
accord with it.
Though all the current in-kernel callers just pass 1 to eventfd_signal(), it
doesn't mean there is no possibility of other usages in future. 
Actually, we're
considering to encode some usefully info to "count" and sent it to 
userspace. :-)