Applied to master, thanks!
On 03/08/2016 15:00, "Jarno Rajahalme" <ja...@ovn.org> wrote:
>Looks good to me,
>
>Acked-by: Jarno Rajahalme <ja...@ovn.org>
>
>> On Aug 2, 2016, at 5:03 PM, Daniele Di Proietto <diproiet...@vmware.com>
>> wrote:
>>
>> With RCU in Open vSwitch it's very easy to protect objects accessed by
>> a pointer, but sometimes a pointer is not available.
>>
>> One example is the vhost id for DPDK 16.07. Until DPDK 16.04 a pointer
>> was used to access a vhost device with RCU semantics. From DPDK 16.07
>> an integer id (which is an array index) is used to access a vhost
>> device. Ideally, we want the exact same RCU semantics that we had for
>> the pointer, on the integer (atomicity, memory barriers, behaviour
>> around quiescent states)
>>
>> This commit implements a new type in ovs-rcu: ovsrcu_index. The newly
>> implemented ovsrcu_index_*() functions should be used to access the
>> type.
>>
>> Even though we say "Do not, in general, declare a typedef for a struct,
>> union, or enum.", I think we're not in the "general" case.
>>
>> Signed-off-by: Daniele Di Proietto <diproiet...@vmware.com>
>> ---
>> lib/ovs-rcu.h | 84
>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 84 insertions(+)
>>
>> diff --git a/lib/ovs-rcu.h b/lib/ovs-rcu.h
>> index dc75749..2887bb8 100644
>> --- a/lib/ovs-rcu.h
>> +++ b/lib/ovs-rcu.h
>> @@ -125,6 +125,36 @@
>> * ovs_mutex_unlock(&mutex);
>> * }
>> *
>> + * In some rare cases an object may not be addressable with a pointer, but
>> only
>> + * through an array index (e.g. because it's provided by another library).
>> It
>> + * is still possible to have RCU semantics by using the ovsrcu_index type.
>> + *
>> + * static struct ovs_mutex mutex = OVS_MUTEX_INITIALIZER;
>> + *
>> + * ovsrcu_index port_id;
>> + *
>> + * void tx()
>> + * {
>> + * int id = ovsrcu_index_get(&port_id);
>> + * if (id == -1) {
>> + * return;
>> + * }
>> + * port_tx(id);
>> + * }
>> + *
>> + * void delete()
>> + * {
>> + * int id;
>> + *
>> + * ovs_mutex_lock(&mutex);
>> + * id = ovsrcu_index_get_protected(&port_id);
>> + * ovsrcu_index_set(&port_id, -1);
>> + * ovs_mutex_unlock(&mutex);
>> + *
>> + * ovsrcu_synchronize();
>> + * port_delete(id);
>> + * }
>> + *
>> */
>>
>> #include "compiler.h"
>> @@ -213,6 +243,60 @@ void ovsrcu_postpone__(void (*function)(void *aux),
>> void *aux);
>> (void) sizeof(*(ARG)), \
>> ovsrcu_postpone__((void (*)(void *))(FUNCTION), ARG))
>>
>> +/* An array index protected by RCU semantics. This is an easier
>> alternative to
>> + * an RCU protected pointer to a malloc'd int. */
>> +typedef struct { atomic_int v; } ovsrcu_index;
>> +
>> +static inline int ovsrcu_index_get__(const ovsrcu_index *i, memory_order
>> order)
>> +{
>> + int ret;
>> + atomic_read_explicit(CONST_CAST(atomic_int *, &i->v), &ret, order);
>> + return ret;
>> +}
>> +
>> +/* Returns the index contained in 'i'. The returned value can be used until
>> + * the next grace period. */
>> +static inline int ovsrcu_index_get(const ovsrcu_index *i)
>> +{
>> + return ovsrcu_index_get__(i, memory_order_consume);
>> +}
>> +
>> +/* Returns the index contained in 'i'. This is an alternative to
>> + * ovsrcu_index_get() that can be used when there's no possible concurrent
>> + * writer. */
>> +static inline int ovsrcu_index_get_protected(const ovsrcu_index *i)
>> +{
>> + return ovsrcu_index_get__(i, memory_order_relaxed);
>> +}
>> +
>> +static inline void ovsrcu_index_set__(ovsrcu_index *i, int value,
>> + memory_order order)
>> +{
>> + atomic_store_explicit(&i->v, value, order);
>> +}
>> +
>> +/* Writes the index 'value' in 'i'. The previous value of 'i' may still be
>> + * used by readers until the next grace period. */
>> +static inline void ovsrcu_index_set(ovsrcu_index *i, int value)
>> +{
>> + ovsrcu_index_set__(i, value, memory_order_release);
>> +}
>> +
>> +/* Writes the index 'value' in 'i'. This is an alternative to
>> + * ovsrcu_index_set() that can be used when there's no possible concurrent
>> + * reader. */
>> +static inline void ovsrcu_index_set_hidden(ovsrcu_index *i, int value)
>> +{
>> + ovsrcu_index_set__(i, value, memory_order_relaxed);
>> +}
>> +
>> +/* Initializes 'i' with 'value'. This is safe to call as long as there are
>> no
>> + * concurrent readers. */
>> +static inline void ovsrcu_index_init(ovsrcu_index *i, int value)
>> +{
>> + atomic_init(&i->v, value);
>> +}
>> +
>> /* Quiescent states. */
>> void ovsrcu_quiesce_start(void);
>> void ovsrcu_quiesce_end(void);
>> --
>> 2.8.1
>>
>
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