Better error messages for short reads/writes in SLRU

This avoids getting a

    Could not read from file ...: Success.

for a short read or write (since errno is not set in that case).
Instead, report a more specific error messages.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/5de61b6b-8be9-7771-0048-860328efe027%402ndquadrant.com

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 2dbc65b125ba8d4adfbf08aa2e40176e8463ddc3..3903a130a1f9446328cd55d37d8fce68696de8b1 100644 (file)
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -920,18 +920,29 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
                                                           path, offset)));
                        break;
                case SLRU_READ_FAILED:
-                       ereport(ERROR,
-                                       (errcode_for_file_access(),
-                                        errmsg("could not access status of transaction %u", xid),
-                                        errdetail("Could not read from file \"%s\" at offset %u: %m.",
-                                                          path, offset)));
+                       if (errno)
+                               ereport(ERROR,
+                                               (errcode_for_file_access(),
+                                                errmsg("could not access status of transaction %u", xid),
+                                                errdetail("Could not read from file \"%s\" at offset %u: %m.",
+                                                                  path, offset)));
+                       else
+                               ereport(ERROR,
+                                               (errmsg("could not access status of transaction %u", xid),
+                                                errdetail("Could not read from file \"%s\" at offset %u: read too few bytes.", path, offset)));
                        break;
                case SLRU_WRITE_FAILED:
-                       ereport(ERROR,
-                                       (errcode_for_file_access(),
-                                        errmsg("could not access status of transaction %u", xid),
-                                        errdetail("Could not write to file \"%s\" at offset %u: %m.",
-                                                          path, offset)));
+                       if (errno)
+                               ereport(ERROR,
+                                               (errcode_for_file_access(),
+                                                errmsg("could not access status of transaction %u", xid),
+                                                errdetail("Could not write to file \"%s\" at offset %u: %m.",
+                                                                  path, offset)));
+                       else
+                               ereport(ERROR,
+                                               (errmsg("could not access status of transaction %u", xid),
+                                                errdetail("Could not write to file \"%s\" at offset %u: wrote too few bytes.",
+                                                                  path, offset)));
                        break;
                case SLRU_FSYNC_FAILED:
                        ereport(data_sync_elevel(ERROR),