Suspend exclusive database lock when scriptlets get called, allowing
read access in scriptlets. Only needed for DB_PRIVATE (aka global)
locking.

--- ./lib/backend/db3.c.orig	2019-10-02 09:56:46.416347458 +0000
+++ ./lib/backend/db3.c	2019-10-02 09:56:52.084335992 +0000
@@ -552,6 +552,46 @@ static void db3_dbSetFSync(rpmdb rdb, in
 
 static int db3_Ctrl(rpmdb rdb, dbCtrlOp ctrl)
 {
+    struct flock l;
+    int tries;
+    int fdno = -1;
+    dbiIndex dbi;
+    DB * db;
+
+    switch (ctrl) {
+    case DB_CTRL_SUSPEND_DBLOCK:
+    case DB_CTRL_RESUME_DBLOCK:
+	dbi = rdb->db_pkgs;	/* packages db only */
+	if (!dbi)
+	    return 1;
+	if (!dbi->cfg.dbi_lockdbfd || (dbi->dbi_flags & DBI_VERIFYONLY) != 0)
+	    return 0;
+	if (!(dbi->dbi_rpmdb->db_mode & (O_RDWR|O_WRONLY)))
+	    return 0;
+	if (_lockdbfd == 0)
+	    return 0;
+        db = dbi->dbi_db;
+	if (!(db->fd(db, &fdno) == 0 && fdno >= 0))
+	    return 1;
+	for (tries = 0; tries < 2; tries++) {
+	    memset(&l, 0, sizeof(l));
+	    l.l_whence = 0;
+	    l.l_start = 0;
+	    l.l_len = 0;
+	    l.l_type = ctrl == DB_CTRL_SUSPEND_DBLOCK ? F_RDLCK : F_WRLCK;
+	    if (!fcntl(fdno, tries ? F_SETLKW : F_SETLK, (void *)&l))
+		return 0;
+	    if (ctrl == DB_CTRL_SUSPEND_DBLOCK) {
+		rpmlog(RPMLOG_WARNING, _("could not suspend database lock\n"));
+		return 1;
+	    }
+	    if (tries == 0)
+		rpmlog(RPMLOG_WARNING, _("waiting to reestablish exclusive database lock\n"));
+	}
+	return 1;
+    default:
+        break;
+    }
     return 0;
 }
 
--- ./lib/backend/dbi.h.orig	2019-10-02 09:56:46.416347458 +0000
+++ ./lib/backend/dbi.h	2019-10-02 09:56:52.084335992 +0000
@@ -17,7 +17,9 @@ typedef enum dbCtrlOp_e {
     DB_CTRL_UNLOCK_RO		= 2,
     DB_CTRL_LOCK_RW		= 3,
     DB_CTRL_UNLOCK_RW		= 4,
-    DB_CTRL_INDEXSYNC		= 5
+    DB_CTRL_INDEXSYNC		= 5,
+    DB_CTRL_SUSPEND_DBLOCK      = 100,
+    DB_CTRL_RESUME_DBLOCK       = 101
 } dbCtrlOp;
 
 typedef struct dbiIndex_s * dbiIndex;
--- ./lib/rpmdb.c.orig	2019-10-02 09:56:46.416347458 +0000
+++ ./lib/rpmdb.c	2019-10-02 09:56:52.084335992 +0000
@@ -2644,6 +2644,12 @@ int rpmdbCtrl(rpmdb db, rpmdbCtrlOp ctrl
     case RPMDB_CTRL_INDEXSYNC:
 	dbctrl = DB_CTRL_INDEXSYNC;
 	break;
+    case RPMDB_CTRL_SUSPEND_DBLOCK:
+	dbctrl = DB_CTRL_SUSPEND_DBLOCK;
+	break;
+    case RPMDB_CTRL_RESUME_DBLOCK:
+	dbctrl = DB_CTRL_RESUME_DBLOCK;
+	break;
     }
     return dbctrl ? dbCtrl(db, dbctrl) : 1;
 }
--- ./lib/rpmdb.h.orig	2019-06-26 14:17:31.412985694 +0000
+++ ./lib/rpmdb.h	2019-10-02 09:56:52.088335984 +0000
@@ -35,7 +35,9 @@ typedef enum rpmdbCtrlOp_e {
     RPMDB_CTRL_UNLOCK_RO       = 2,
     RPMDB_CTRL_LOCK_RW         = 3,
     RPMDB_CTRL_UNLOCK_RW       = 4,
-    RPMDB_CTRL_INDEXSYNC       = 5
+    RPMDB_CTRL_INDEXSYNC       = 5,
+    RPMDB_CTRL_SUSPEND_DBLOCK  = 100,
+    RPMDB_CTRL_RESUME_DBLOCK   = 101
 } rpmdbCtrlOp;
 
 /** \ingroup rpmdb
--- ./lib/transaction.c.orig	2019-10-02 09:56:52.088335984 +0000
+++ ./lib/transaction.c	2019-10-02 09:58:36.956123870 +0000
@@ -1601,6 +1601,7 @@ rpmRC runScript(rpmts ts, rpmte te, Head
     rpmTagVal stag = rpmScriptTag(script);
     FD_t sfd = NULL;
     int warn_only = !(rpmScriptFlags(script) & RPMSCRIPT_FLAG_CRITICAL);
+    rpmdb rdb = rpmtsGetRdb(ts);
 
     /* Create a temporary transaction element for triggers from rpmdb */
     if (te == NULL) {
@@ -1612,10 +1613,12 @@ rpmRC runScript(rpmts ts, rpmte te, Head
     if (sfd == NULL)
 	sfd = rpmtsScriptFd(ts);
 
+    rpmdbCtrl(rdb, RPMDB_CTRL_SUSPEND_DBLOCK);
     rpmswEnter(rpmtsOp(ts, RPMTS_OP_SCRIPTLETS), 0);
     rc = rpmScriptRun(script, arg1, arg2, sfd,
 		      prefixes, rpmtsPlugins(ts));
     rpmswExit(rpmtsOp(ts, RPMTS_OP_SCRIPTLETS), 0);
+    rpmdbCtrl(rdb, RPMDB_CTRL_RESUME_DBLOCK);
 
     /* Map warn-only errors to "notfound" for script stop callback */
     stoprc = (rc != RPMRC_OK && warn_only) ? RPMRC_NOTFOUND : rc;