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-rw-r--r--Documentation/livepatch/shadow-vars.txt41
1 files changed, 29 insertions, 12 deletions
diff --git a/Documentation/livepatch/shadow-vars.txt b/Documentation/livepatch/shadow-vars.txt
index 89c66634d600..ecc09a7be5dd 100644
--- a/Documentation/livepatch/shadow-vars.txt
+++ b/Documentation/livepatch/shadow-vars.txt
@@ -34,9 +34,13 @@ meta-data and shadow-data:
- data[] - storage for shadow data
It is important to note that the klp_shadow_alloc() and
-klp_shadow_get_or_alloc() calls, described below, store a *copy* of the
-data that the functions are provided. Callers should provide whatever
-mutual exclusion is required of the shadow data.
+klp_shadow_get_or_alloc() are zeroing the variable by default.
+They also allow to call a custom constructor function when a non-zero
+value is needed. Callers should provide whatever mutual exclusion
+is required.
+
+Note that the constructor is called under klp_shadow_lock spinlock. It allows
+to do actions that can be done only once when a new variable is allocated.
* klp_shadow_get() - retrieve a shadow variable data pointer
- search hashtable for <obj, id> pair
@@ -47,7 +51,7 @@ mutual exclusion is required of the shadow data.
- WARN and return NULL
- if <obj, id> doesn't already exist
- allocate a new shadow variable
- - copy data into the new shadow variable
+ - initialize the variable using a custom constructor and data when provided
- add <obj, id> to the global hashtable
* klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable
@@ -56,16 +60,20 @@ mutual exclusion is required of the shadow data.
- return existing shadow variable
- if <obj, id> doesn't already exist
- allocate a new shadow variable
- - copy data into the new shadow variable
+ - initialize the variable using a custom constructor and data when provided
- add <obj, id> pair to the global hashtable
* klp_shadow_free() - detach and free a <obj, id> shadow variable
- find and remove a <obj, id> reference from global hashtable
- - if found, free shadow variable
+ - if found
+ - call destructor function if defined
+ - free shadow variable
* klp_shadow_free_all() - detach and free all <*, id> shadow variables
- find and remove any <*, id> references from global hashtable
- - if found, free shadow variable
+ - if found
+ - call destructor function if defined
+ - free shadow variable
2. Use cases
@@ -107,7 +115,8 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
sta = kzalloc(sizeof(*sta) + hw->sta_data_size, gfp);
/* Attach a corresponding shadow variable, then initialize it */
- ps_lock = klp_shadow_alloc(sta, PS_LOCK, NULL, sizeof(*ps_lock), gfp);
+ ps_lock = klp_shadow_alloc(sta, PS_LOCK, sizeof(*ps_lock), gfp,
+ NULL, NULL);
if (!ps_lock)
goto shadow_fail;
spin_lock_init(ps_lock);
@@ -131,7 +140,7 @@ variable:
void sta_info_free(struct ieee80211_local *local, struct sta_info *sta)
{
- klp_shadow_free(sta, PS_LOCK);
+ klp_shadow_free(sta, PS_LOCK, NULL);
kfree(sta);
...
@@ -148,16 +157,24 @@ shadow variables to parents already in-flight.
For commit 1d147bfa6429, a good spot to allocate a shadow spinlock is
inside ieee80211_sta_ps_deliver_wakeup():
+int ps_lock_shadow_ctor(void *obj, void *shadow_data, void *ctor_data)
+{
+ spinlock_t *lock = shadow_data;
+
+ spin_lock_init(lock);
+ return 0;
+}
+
#define PS_LOCK 1
void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
{
- DEFINE_SPINLOCK(ps_lock_fallback);
spinlock_t *ps_lock;
/* sync with ieee80211_tx_h_unicast_ps_buf */
ps_lock = klp_shadow_get_or_alloc(sta, PS_LOCK,
- &ps_lock_fallback, sizeof(ps_lock_fallback),
- GFP_ATOMIC);
+ sizeof(*ps_lock), GFP_ATOMIC,
+ ps_lock_shadow_ctor, NULL);
+
if (ps_lock)
spin_lock(ps_lock);
...