Update obsolete comment: it's no longer the case that mdread() will allow

reads beyond EOF, except by special coercion.

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index bbb6e0bc04afdcb027dd9a4e8ddbf6188e2d4e09..fb09389e4eb112c0ed1e89029bff0e674cc1fe3a 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.220 2007/05/30 20:11:58 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.221 2007/06/18 00:47:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -223,15 +223,14 @@ ReadBuffer_common(Relation reln, BlockNumber blockNum, bool zeroPage,
         * We get here only in the corner case where we are trying to extend
         * the relation but we found a pre-existing buffer marked BM_VALID.
         * This can happen because mdread doesn't complain about reads beyond
-        * EOF --- which is arguably bogus, but changing it seems tricky ---
-        * and so a previous attempt to read a block just beyond EOF could
-        * have left a "valid" zero-filled buffer.  Unfortunately, we have
-        * also seen this case occurring because of buggy Linux kernels that
-        * sometimes return an lseek(SEEK_END) result that doesn't account for
-        * a recent write.  In that situation, the pre-existing buffer would
-        * contain valid data that we don't want to overwrite.  Since the
-        * legitimate cases should always have left a zero-filled buffer,
-        * complain if not PageIsNew.
+        * EOF (when zero_damaged_pages is ON) and so a previous attempt to
+        * read a block beyond EOF could have left a "valid" zero-filled
+        * buffer.  Unfortunately, we have also seen this case occurring
+        * because of buggy Linux kernels that sometimes return an
+        * lseek(SEEK_END) result that doesn't account for a recent write.
+        * In that situation, the pre-existing buffer would contain valid data
+        * that we don't want to overwrite.  Since the legitimate case should
+        * always have left a zero-filled buffer, complain if not PageIsNew.
         */
        bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr);
        if (!PageIsNew((PageHeader) bufBlock))