From: Magnus Hagander <magnus@hagander.net>
Date: Fri, 18 May 2018 15:53:17 +0000 (+0200)
Subject: Fix error message on short read of pg_control
X-Git-Tag: REL9_5_14~75
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=714d8e5fa1b21a1113d6cd444af5cbc9d67d566f;p=postgresql

Fix error message on short read of pg_control

Instead of saying "error: success", indicate that we got a working read
but it was too short.
---

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 527ce760e4..5d845a8178 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -4258,6 +4258,7 @@ ReadControlFile(void)
 {
 	pg_crc32c	crc;
 	int			fd;
+	int			r;
 
 	/*
 	 * Read data...
@@ -4271,10 +4272,17 @@ ReadControlFile(void)
 				 errmsg("could not open control file \"%s\": %m",
 						XLOG_CONTROL_FILE)));
 
-	if (read(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
-		ereport(PANIC,
-				(errcode_for_file_access(),
-				 errmsg("could not read from control file: %m")));
+	r = read(fd, ControlFile, sizeof(ControlFileData));
+	if (r != sizeof(ControlFileData))
+	{
+		if (r < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read from control file: %m")));
+		else
+			ereport(PANIC,
+					 (errmsg("could not read from control file: read %d bytes, expected %d", r, (int) sizeof(ControlFileData))));
+	}
 
 	close(fd);