[Xen-devel] Re: [PATCH] change acquire/release_console_sem() to console_lock/unlock()

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

On Fri, 21 Jan 2011 09:10:06 +0100 Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> 
wrote:

> include/linux/mutex.h:
> 
> /*
>  * NOTE: mutex_trylock() follows the spin_trylock() convention,
>  *       not the down_trylock() convention!
>  *
>  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
>  */
> extern int mutex_trylock(struct mutex *lock);
> 
> So that's why the return value was inverted (when treating it as a boolean).
> I can understand that.
> 
> However:
> 
> +/**
> + * console_trylock - try to lock the console system for exclusive use.
> + *
> + * Tried to acquire a lock which guarantees that the caller has
> + * exclusive access to the console system and the console_drivers list.
> + *
> + * returns -1 on success, and 0 on failure to acquire the lock.
> + */
> +int console_trylock(void)
> 
> So this one returns -1 on success, not 1? Why?

Yup.  All callers just test for non-zero, so...

--- 
a/kernel/printk.c~change-acquire-release_console_sem-to-console_lock-unlock-fix-2
+++ a/kernel/printk.c
@@ -1058,7 +1058,7 @@ EXPORT_SYMBOL(console_lock);
  * Tried to acquire a lock which guarantees that the caller has
  * exclusive access to the console system and the console_drivers list.
  *
- * returns -1 on success, and 0 on failure to acquire the lock.
+ * returns 1 on success, and 0 on failure to acquire the lock.
  */
 int console_trylock(void)
 {
@@ -1070,7 +1070,7 @@ int console_trylock(void)
        }
        console_locked = 1;
        console_may_schedule = 0;
-       return -1;
+       return 1;
 }
 EXPORT_SYMBOL(console_trylock);
 
_


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