Don't Insert() a VFD entry until it's fully built.

Otherwise, if FDDEBUG is enabled, the debugging output fails because
it tries to read the fileName, which isn't set up yet (and should in
fact always be NULL).

AFAICT, this has been wrong since Berkeley.  Before 96bf88d52,
it would accidentally fail to crash on platforms where snprintf()
is forgiving about being passed a NULL pointer for %s; but the
file name intended to be included in the debug output wouldn't
ever have shown up.

Report and fix by Greg Nancarrow.  Although this is only visibly
broken in custom-made builds, it still seems worth back-patching
to all supported branches, as the FDDEBUG code is pretty useless
as it stands.

Discussion: https://postgr.es/m/CAJcOf-cUDgm9qYtC_B6XrC6MktMPNRby2p61EtSGZKnfotMArw@mail.gmail.com

diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 03d43fdada1146c822220e9ada69a8a4eb3491f4..7fa6fc996dcd47101bb6a2abbc3fa5cb12ece0df 100644 (file)
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -1323,8 +1323,6 @@ PathNameOpenFile(FileName fileName, int fileFlags, int fileMode)
        DO_DB(elog(LOG, "PathNameOpenFile: success %d",
                           vfdP->fd));
 
-       Insert(file);
-
        vfdP->fileName = fnamecopy;
        /* Saved flags are adjusted to be OK for re-opening file */
        vfdP->fileFlags = fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL);
@@ -1334,6 +1332,8 @@ PathNameOpenFile(FileName fileName, int fileFlags, int fileMode)
        vfdP->fdstate = 0x0;
        vfdP->resowner = NULL;
 
+       Insert(file);
+
        return file;
 }