This change is a tighter rework of
7d85d87f4d5c, which tried to improve
the code so as it would work should PgStat_HashKey gain new fields that
create padding bytes. However, the previous change is proving to not be
enough as some code paths of pgstats do not pass PgStat_HashKey by
reference (valgrind would warn when padding is added to the structure,
through a new field).
Per discussion, let's document and check that PgStat_HashKey has no
padding rather than try to complicate the code of pgstats so as it is
able to work around that.
This removes a couple of memset(0) calls that should not be required.
While on it, this commit adds a static assertion checking that no
padding is introduced in the structure, by checking that the size of
PgStat_HashKey matches with the sum of the size of all its fields.
The object ID part of the hash key is already 8 bytes, which should be
plenty enough already. A comment is added to discourage the addition of
new fields.
Author: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAA5RZ0t9omat+HVSakJXwTMWvhpYFcAZb41RPWKwrKFUgmAFBQ@mail.gmail.com
index f8e91484e36be1a314eb542dfb8d28b111beee11..73c2ced3f4e2b7be4baed9bd343d12f84c4bd8dc 100644 (file)
void *
pgstat_fetch_entry(PgStat_Kind kind, Oid dboid, uint64 objid)
{
- PgStat_HashKey key;
+ PgStat_HashKey key = {0};
PgStat_EntryRef *entry_ref;
void *stats_data;
const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
@@ -943,9 +943,6 @@ pgstat_fetch_entry(PgStat_Kind kind, Oid dboid, uint64 objid)
pgstat_prep_snapshot();
- /* clear padding */
- memset(&key, 0, sizeof(struct PgStat_HashKey));
-
key.kind = kind;
key.dboid = dboid;
key.objid = objid;
index 9dc3212f7dd0103e57ff19b9fcfa6d2b996cf7cb..ca36fd247f64219c320347bdda3ad9aea63dee5d 100644 (file)
pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, uint64 objid, bool create,
bool *created_entry)
{
- PgStat_HashKey key;
+ PgStat_HashKey key = {0};
PgStatShared_HashEntry *shhashent;
PgStatShared_Common *shheader = NULL;
PgStat_EntryRef *entry_ref;
- /* clear padding */
- memset(&key, 0, sizeof(struct PgStat_HashKey));
-
key.kind = kind;
key.dboid = dboid;
key.objid = objid;
bool
pgstat_drop_entry(PgStat_Kind kind, Oid dboid, uint64 objid)
{
- PgStat_HashKey key;
+ PgStat_HashKey key = {0};
PgStatShared_HashEntry *shent;
bool freed = true;
- /* clear padding */
- memset(&key, 0, sizeof(struct PgStat_HashKey));
-
key.kind = kind;
key.dboid = dboid;
key.objid = objid;
index 6cf00008f6333575f3f160fab6f32c61f7c2d4c7..bf75ebcef31ce6be0a287f2c8c715e82f11e9912 100644 (file)
* PgStatShared_Common as the first element.
*/
-/* struct for shared statistics hash entry key. */
+/*
+ * Struct for shared statistics hash entry key.
+ *
+ * NB: We assume that this struct contains no padding. Also, 8 bytes
+ * allocated for the object ID are good enough to ensure the uniqueness
+ * of the hash key, hence the addition of new fields is not recommended.
+ */
typedef struct PgStat_HashKey
{
PgStat_Kind kind; /* statistics entry kind */
* identifier. */
} PgStat_HashKey;
+/*
+ * PgStat_HashKey should not have any padding. Checking that the structure
+ * size matches with the sum of each field is a check simple enough to
+ * enforce this policy.
+ */
+StaticAssertDecl((sizeof(PgStat_Kind) + sizeof(uint64) + sizeof(Oid)) ==
+ sizeof(PgStat_HashKey),
+ "PgStat_HashKey should have no padding");
+
/*
* Shared statistics hash entry. Doesn't itself contain any stats, but points
* to them (with ->body). That allows the stats entries themselves to be of