When performing a base backup, check for read errors.

robertmhaas · robertmhaas · commit 62fb12d7e138 · 2019-09-06T08:56:45.000-04:00
The old code didn't differentiate between a read error and a concurrent truncation. fread reports both of these by returning 0; you have to use feof() or ferror() to distinguish between them, which this code did not do. It might be a better idea to use read() rather than fread() here, so that we can display a less-generic error message, but I'm not sure that would qualify as a back-patchable bug fix, so just do this much for now. Jeevan Chalke, reviewed by Jeevan Ladhe and by me. Discussion: http://postgr.es/m/CA+TgmobG4ywMzL5oQq2a8YKp8x2p3p1LOMMcGqpS7aekT9+ETA@mail.gmail.com
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
@@ -85,6 +85,18 @@ static char *statrelpath = NULL;
  */
 #define THROTTLING_FREQUENCY	8
 
+/*
+ * Checks whether we encountered any error in fread().  fread() doesn't give
+ * any clue what has happened, so we check with ferror().  Also, neither
+ * fread() nor ferror() set errno, so we just throw a generic error.
+ */
+#define CHECK_FREAD_ERROR(fp, filename) \
+do { \
+	if (ferror(fp)) \
+		ereport(ERROR, \
+				(errmsg("could not read from file \"%s\"", filename))); \
+} while (0)
+
 /* The actual number of bytes, transfer of which may cause sleep. */
 static uint64 throttling_sample;
 
@@ -509,6 +521,8 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 					break;
 			}
 
+			CHECK_FREAD_ERROR(fp, pathbuf);
+
 			if (len != XLogSegSize)
 			{
 				CheckXLogRemoved(segno, tli);
@@ -1245,6 +1259,8 @@ sendFile(char *readfilename, char *tarfilename, struct stat *statbuf,
 		}
 	}
 
+	CHECK_FREAD_ERROR(fp, readfilename);
+
 	/* If the file was truncated while we were sending it, pad it with zeros */
 	if (len < statbuf->st_size)
 	{
