pg_waldump: Fix error message for WAL files smaller than XLOG_BLCKSZ.

When opening a WAL file smaller than XLOG_BLCKSZ (e.g. 0 bytes long) while
determining the wal_segment_size, pg_waldump checked errno, despite errno not
being set by the short read. Resulting in a bogus error message.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20220214.181847.775024684568733277.horikyota.ntt@gmail.com
Backpatch: 11-, the bug was introducedin fc49e24fa

diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 0fee1ebdee155a23671961328c02ad3230a29160..b1e5f4610455c70182d6adedb772213389e21e76 100644 (file)
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -207,15 +207,12 @@ search_directory(const char *directory, const char *fname)
                                                                         WalSegSz),
                                                        fname, WalSegSz);
                }
+               else if (r < 0)
+                       fatal_error("could not read file \"%s\": %s",
+                                               fname, strerror(errno));
                else
-               {
-                       if (errno != 0)
-                               fatal_error("could not read file \"%s\": %s",
-                                                       fname, strerror(errno));
-                       else
-                               fatal_error("could not read file \"%s\": read %d of %zu",
-                                                       fname, r, (Size) XLOG_BLCKSZ);
-               }
+                       fatal_error("could not read file \"%s\": read %d of %zu",
+                                               fname, r, (Size) XLOG_BLCKSZ);
                close(fd);
                return true;
        }