Use integer backend type when exec'ing a postmaster child

This way we don't have to walk the entire process type array and
strcmp() the string with the names therein.  The integer value can be
directly used as array index instead.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Euler Taveira <euler@eulerto.com>
Discussion: https://postgr.es/m/202512090935.k3xrtr44hxkn@alvherre.pgsql

diff --git a/src/backend/postmaster/launch_backend.c b/src/backend/postmaster/launch_backend.c
index eb91503522f4a81732655c7e1bc47e9c3c42d85b..cea229ad6a44c975a8c456d9e2c9352888a9aef1 100644 (file)
--- a/src/backend/postmaster/launch_backend.c
+++ b/src/backend/postmaster/launch_backend.c
@@ -162,7 +162,7 @@ static bool save_backend_variables(BackendParameters *param, int child_slot,
 #endif
                                                                   const void *startup_data, size_t startup_data_len);
 
-static pid_t internal_forkexec(const char *child_kind, int child_slot,
+static pid_t internal_forkexec(BackendType child_kind, int child_slot,
                                                           const void *startup_data, size_t startup_data_len,
                                                           ClientSocket *client_sock);
 
@@ -217,7 +217,7 @@ postmaster_child_launch(BackendType child_type, int child_slot,
                ((BackendStartupData *) startup_data)->fork_started = GetCurrentTimestamp();
 
 #ifdef EXEC_BACKEND
-       pid = internal_forkexec(child_process_kinds[child_type].name, child_slot,
+       pid = internal_forkexec(child_type, child_slot,
                                                        startup_data, startup_data_len, client_sock);
        /* the child process will arrive in SubPostmasterMain */
 #else                                                  /* !EXEC_BACKEND */
@@ -282,7 +282,7 @@ postmaster_child_launch(BackendType child_type, int child_slot,
  * - fork():s, and then exec():s the child process
  */
 static pid_t
-internal_forkexec(const char *child_kind, int child_slot,
+internal_forkexec(BackendType child_kind, int child_slot,
                                  const void *startup_data, size_t startup_data_len, ClientSocket *client_sock)
 {
        static unsigned long tmpBackendFileNum = 0;
@@ -358,7 +358,7 @@ internal_forkexec(const char *child_kind, int child_slot,
 
        /* set up argv properly */
        argv[0] = "postgres";
-       snprintf(forkav, MAXPGPATH, "--forkchild=%s", child_kind);
+       snprintf(forkav, MAXPGPATH, "--forkchild=%d", (int) child_kind);
        argv[1] = forkav;
        /* Insert temp file name after --forkchild argument */
        argv[2] = tmpfilename;
@@ -392,7 +392,7 @@ internal_forkexec(const char *child_kind, int child_slot,
  *      file is complete.
  */
 static pid_t
-internal_forkexec(const char *child_kind, int child_slot,
+internal_forkexec(BackendType child_kind, int child_slot,
                                  const void *startup_data, size_t startup_data_len, ClientSocket *client_sock)
 {
        int                     retry_count = 0;
@@ -444,8 +444,8 @@ retry:
 #else
        sprintf(paramHandleStr, "%lu", (DWORD) paramHandle);
 #endif
-       l = snprintf(cmdLine, sizeof(cmdLine) - 1, "\"%s\" --forkchild=\"%s\" %s",
-                                postgres_exec_path, child_kind, paramHandleStr);
+       l = snprintf(cmdLine, sizeof(cmdLine) - 1, "\"%s\" --forkchild=%d %s",
+                                postgres_exec_path, (int) child_kind, paramHandleStr);
        if (l >= sizeof(cmdLine))
        {
                ereport(LOG,
@@ -567,8 +567,8 @@ retry:
  *                     to what it would be if we'd simply forked on Unix, and then
  *                     dispatch to the appropriate place.
  *
- * The first two command line arguments are expected to be "--forkchild=<name>",
- * where <name> indicates which postmaster child we are to become, and
+ * The first two command line arguments are expected to be "--forkchild=<kind>",
+ * where <kind> indicates which process type we are to become, and
  * the name of a variables file that we can read to load data that would
  * have been inherited by fork() on Unix.
  */
@@ -579,7 +579,6 @@ SubPostmasterMain(int argc, char *argv[])
        size_t          startup_data_len;
        char       *child_kind;
        BackendType child_type;
-       bool            found = false;
        TimestampTz fork_end;
 
        /* In EXEC_BACKEND case we will not have inherited these settings */
@@ -599,21 +598,15 @@ SubPostmasterMain(int argc, char *argv[])
        if (argc != 3)
                elog(FATAL, "invalid subpostmaster invocation");
 
-       /* Find the entry in child_process_kinds */
+       /*
+        * Parse the --forkchild argument to find our process type.  We rely with
+        * malice aforethought on atoi returning 0 (B_INVALID) on error.
+        */
        if (strncmp(argv[1], "--forkchild=", 12) != 0)
                elog(FATAL, "invalid subpostmaster invocation (--forkchild argument missing)");
        child_kind = argv[1] + 12;
-       found = false;
-       for (int idx = 0; idx < lengthof(child_process_kinds); idx++)
-       {
-               if (strcmp(child_process_kinds[idx].name, child_kind) == 0)
-               {
-                       child_type = (BackendType) idx;
-                       found = true;
-                       break;
-               }
-       }
-       if (!found)
+       child_type = (BackendType) atoi(child_kind);
+       if (child_type <= B_INVALID || child_type > BACKEND_NUM_TYPES - 1)
                elog(ERROR, "unknown child kind %s", child_kind);
 
        /* Read in the variables file */