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Introduce private data area for injection points

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This commit extends the backend-side infrastructure of injection points
so as it becomes possible to register some input data when attaching a
point.  This private data can be registered with the function name and
the library name of the callback when attaching a point, then it is
given as input argument to the callback.  This gives the possibility for
modules to pass down custom data at runtime when attaching a point
without managing that internally, in a manner consistent with the
callback entry retrieved from the hash shmem table storing the injection
point data.

InjectionPointAttach() gains two arguments, to be able to define the
private data contents and its size.

A follow-up commit will rely on this infrastructure to close a race
condition with the injection point detach in the module
injection_points.

While on it, this changes InjectionPointDetach() to return a boolean,
returning false if a point cannot be detached.  This has been mentioned
by Noah as useful when it comes to implement more complex tests with
concurrent point detach, solid with the automatic detach done for local
points in the test module.

Documentation is adjusted in consequence.

Per discussion with Noah Misch.

Reviewed-by: Noah Misch
Discussion: https://postgr.es/m/20240509031553.47@rfd.leadboat.com
This commit is contained in:
Michael Paquier
2024-05-12 18:53:06 +09:00
parent 407e0b023c
commit 33181b48fd
5 changed files with 74 additions and 28 deletions
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55
src/backend/utils/misc/injection_point.c
View File

@@ -42,6 +42,7 @@ static HTAB *InjectionPointHash; /* find points from names */
#define INJ_NAME_MAXLEN 64
#define INJ_LIB_MAXLEN 128
#define INJ_FUNC_MAXLEN 128
#define INJ_PRIVATE_MAXLEN 1024
/* Single injection point stored in InjectionPointHash */
typedef struct InjectionPointEntry
@@ -49,6 +50,12 @@ typedef struct InjectionPointEntry
char name[INJ_NAME_MAXLEN]; /* hash key */
char library[INJ_LIB_MAXLEN]; /* library */
char function[INJ_FUNC_MAXLEN]; /* function */
/*
* Opaque data area that modules can use to pass some custom data to
* callbacks, registered when attached.
*/
char private_data[INJ_PRIVATE_MAXLEN];
} InjectionPointEntry;
#define INJECTION_POINT_HASH_INIT_SIZE 16
@@ -61,6 +68,7 @@ typedef struct InjectionPointEntry
typedef struct InjectionPointCacheEntry
{
char name[INJ_NAME_MAXLEN];
char private_data[INJ_PRIVATE_MAXLEN];
InjectionPointCallback callback;
} InjectionPointCacheEntry;
@@ -73,7 +81,8 @@ static HTAB *InjectionPointCache = NULL;
*/
static void
injection_point_cache_add(const char *name,
InjectionPointCallback callback)
InjectionPointCallback callback,
const void *private_data)
{
InjectionPointCacheEntry *entry;
bool found;
@@ -99,6 +108,8 @@ injection_point_cache_add(const char *name,
Assert(!found);
strlcpy(entry->name, name, sizeof(entry->name));
entry->callback = callback;
if (private_data != NULL)
memcpy(entry->private_data, private_data, INJ_PRIVATE_MAXLEN);
}
/*
@@ -124,11 +135,14 @@ injection_point_cache_remove(const char *name)
* Retrieve an injection point from the local cache, if any.
*/
static InjectionPointCallback
injection_point_cache_get(const char *name)
injection_point_cache_get(const char *name, const void **private_data)
{
bool found;
InjectionPointCacheEntry *entry;
if (private_data)
*private_data = NULL;
/* no callback if no cache yet */
if (InjectionPointCache == NULL)
return NULL;
@@ -137,7 +151,11 @@ injection_point_cache_get(const char *name)
hash_search(InjectionPointCache, name, HASH_FIND, &found);
if (found)
{
if (private_data)
*private_data = entry->private_data;
return entry->callback;
}
return NULL;
}
@@ -186,7 +204,9 @@ InjectionPointShmemInit(void)
void
InjectionPointAttach(const char *name,
const char *library,
const char *function)
const char *function,
const void *private_data,
int private_data_size)
{
#ifdef USE_INJECTION_POINTS
InjectionPointEntry *entry_by_name;
@@ -201,6 +221,9 @@ InjectionPointAttach(const char *name,
if (strlen(function) >= INJ_FUNC_MAXLEN)
elog(ERROR, "injection point function %s too long (maximum of %u)",
function, INJ_FUNC_MAXLEN);
if (private_data_size >= INJ_PRIVATE_MAXLEN)
elog(ERROR, "injection point data too long (maximum of %u)",
INJ_PRIVATE_MAXLEN);
/*
* Allocate and register a new injection point. A new point should not
@@ -223,6 +246,8 @@ InjectionPointAttach(const char *name,
entry_by_name->library[INJ_LIB_MAXLEN - 1] = '\0';
strlcpy(entry_by_name->function, function, sizeof(entry_by_name->function));
entry_by_name->function[INJ_FUNC_MAXLEN - 1] = '\0';
if (private_data != NULL)
memcpy(entry_by_name->private_data, private_data, private_data_size);
LWLockRelease(InjectionPointLock);
@@ -233,8 +258,10 @@ InjectionPointAttach(const char *name,
/*
* Detach an existing injection point.
*
* Returns true if the injection point was detached, false otherwise.
*/
void
bool
InjectionPointDetach(const char *name)
{
#ifdef USE_INJECTION_POINTS
@@ -245,10 +272,12 @@ InjectionPointDetach(const char *name)
LWLockRelease(InjectionPointLock);
if (!found)
elog(ERROR, "injection point \"%s\" not found", name);
return false;
return true;
#else
elog(ERROR, "Injection points are not supported by this build");
return true; /* silence compiler */
#endif
}
@@ -265,6 +294,7 @@ InjectionPointRun(const char *name)
InjectionPointEntry *entry_by_name;
bool found;
InjectionPointCallback injection_callback;
const void *private_data;
LWLockAcquire(InjectionPointLock, LW_SHARED);
entry_by_name = (InjectionPointEntry *)
@@ -286,10 +316,10 @@ InjectionPointRun(const char *name)
* Check if the callback exists in the local cache, to avoid unnecessary
* external loads.
*/
injection_callback = injection_point_cache_get(name);
if (injection_callback == NULL)
if (injection_point_cache_get(name, NULL) == NULL)
{
char path[MAXPGPATH];
InjectionPointCallback injection_callback_local;
/* not found in local cache, so load and register */
snprintf(path, MAXPGPATH, "%s/%s%s", pkglib_path,
@@ -299,18 +329,21 @@ InjectionPointRun(const char *name)
elog(ERROR, "could not find library \"%s\" for injection point \"%s\"",
path, name);
injection_callback = (InjectionPointCallback)
injection_callback_local = (InjectionPointCallback)
load_external_function(path, entry_by_name->function, false, NULL);
if (injection_callback == NULL)
if (injection_callback_local == NULL)
elog(ERROR, "could not find function \"%s\" in library \"%s\" for injection point \"%s\"",
entry_by_name->function, path, name);
/* add it to the local cache when found */
injection_point_cache_add(name, injection_callback);
injection_point_cache_add(name, injection_callback_local,
entry_by_name->private_data);
}
injection_callback(name);
/* Now loaded, so get it. */
injection_callback = injection_point_cache_get(name, &private_data);
injection_callback(name, private_data);
#else
elog(ERROR, "Injection points are not supported by this build");
#endif