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 d31a6b87b859ed7bf0b999c41b94eaa614cd0f82..1091d455cb45298855a71840ecefbd7ac9935a07 100644 (file)
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -1422,8 +1422,6 @@ PathNameOpenFilePerm(const char *fileName, int fileFlags, mode_t 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);
@@ -1433,6 +1431,8 @@ PathNameOpenFilePerm(const char *fileName, int fileFlags, mode_t fileMode)
    vfdP->fdstate = 0x0;
    vfdP->resowner = NULL;
 
+   Insert(file);
+
    return file;
 }