Add ABI extra field to fmgr magic block

This allows derived products to intentionally make their fmgr ABI
incompatible, with a clean error message.

Discussion: https://www.postgresql.org/message-id/flat/55215fda-db31-a045-d6b7-d6f2d2dc9920%40enterprisedb.com

diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 96fd9d2268582773f1b8cdcefe9897ff174c657d..cc1a5200705b2b01085010f0c4a99feb60c81acc 100644 (file)
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -330,6 +330,21 @@ incompatible_module_error(const char *libname,
                           magic_data.version / 100, library_version)));
    }
 
+   /*
+    * Similarly, if the ABI extra field doesn't match, error out.  Other
+    * fields below might also mismatch, but that isn't useful information if
+    * you're using the wrong product altogether.
+    */
+   if (strcmp(module_magic_data->abi_extra, magic_data.abi_extra) != 0)
+   {
+       ereport(ERROR,
+               (errmsg("incompatible library \"%s\": ABI mismatch",
+                       libname),
+                errdetail("Server has ABI \"%s\", library has \"%s\".",
+                          magic_data.abi_extra,
+                          module_magic_data->abi_extra)));
+   }
+
    /*
     * Otherwise, spell out which fields don't agree.
     *

diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index ab7b85c86e14fe01f982cb1dbca53ea4145d00e0..cec663bdff0d7584b70bfb98b061d4e49b92fb9f 100644 (file)
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -458,6 +458,7 @@ typedef struct
    int         indexmaxkeys;   /* INDEX_MAX_KEYS */
    int         namedatalen;    /* NAMEDATALEN */
    int         float8byval;    /* FLOAT8PASSBYVAL */
+   char        abi_extra[32];  /* see pg_config_manual.h */
 } Pg_magic_struct;
 
 /* The actual data block contents */
@@ -468,9 +469,13 @@ typedef struct
    FUNC_MAX_ARGS, \
    INDEX_MAX_KEYS, \
    NAMEDATALEN, \
-   FLOAT8PASSBYVAL \
+   FLOAT8PASSBYVAL, \
+   FMGR_ABI_EXTRA, \
 }
 
+StaticAssertDecl(sizeof(FMGR_ABI_EXTRA) <= sizeof(((Pg_magic_struct*)0)->abi_extra),
+                "FMGR_ABI_EXTRA too long");
+
 /*
  * Declare the module magic function.  It needs to be a function as the dlsym
  * in the backend is only guaranteed to work on functions, not data

diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 614035e2159ef387c04752ab5c3f2fb7ee683279..225c5b87cc799f3e1ada8c085582c6b5ca757cc7 100644 (file)
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -42,6 +42,23 @@
  */
 #define FUNC_MAX_ARGS      100
 
+/*
+ * When creating a product derived from PostgreSQL with changes that cause
+ * incompatibilities for loadable modules, it is recommended to change this
+ * string so that dfmgr.c can refuse to load incompatible modules with a clean
+ * error message.  Typical examples that cause incompatibilities are any
+ * changes to node tags or node structures.  (Note that dfmgr.c already
+ * detects common sources of incompatibilities due to major version
+ * differences and due to some changed compile-time constants.  This setting
+ * is for catching anything that cannot be detected in a straightforward way.)
+ *
+ * There is no prescribed format for the string.  The suggestion is to include
+ * product or company name, and optionally any internally-relevant ABI
+ * version.  Example: "ACME Postgres/1.2".  Note that the string will appear
+ * in a user-facing error message if an ABI mismatch is detected.
+ */
+#define FMGR_ABI_EXTRA     "PostgreSQL"
+
 /*
  * Maximum number of columns in an index.  There is little point in making
  * this anything but a multiple of 32, because the main cost is associated