Have BufFileSize() ereport() on FileSize() failure.

petergeoghegan · petergeoghegan · commit 95c45718126f · 2018-11-28T14:42:52.000-08:00
Move the responsibility for checking for and reporting a failure from the only current BufFileSize() caller, logtape.c, to BufFileSize() itself. Code within buffile.c is generally responsible for interfacing with fd.c to report irrecoverable failures. This seems like a convention that's worth sticking to. Reorganizing things this way makes it easy to make the error message raised in the event of BufFileSize() failure descriptive of the underlying problem. We're now clear on the distinction between temporary file name and BufFile name, and can show errno, confident that its value actually relates to the error being reported. In passing, an existing, similar buffile.c ereport() + errcode_for_file_access() site is changed to follow the same conventions. The API of the function BufFileSize() is changed by this commit, despite already being in a stable release (Postgres 11). This seems acceptable, since the BufFileSize() ABI was changed by commit aa55183, which hasn't made it into a point release yet. Besides, it's difficult to imagine a third party BufFileSize() caller not just raising an error anyway, since BufFile state should be considered corrupt when BufFileSize() fails. Per complaint from Tom Lane. Discussion: https://postgr.es/m/26974.1540826748@sss.pgh.pa.us Backpatch: 11-, where shared BufFiles were introduced.
diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
@@ -314,7 +314,8 @@ BufFileOpenShared(SharedFileSet *fileset, const char *name)
 	if (nfiles == 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not open BufFile \"%s\"", name)));
+				 errmsg("could not open temporary file \"%s\" from BufFile \"%s\": %m",
+						segment_name, name)));
 
 	file = makeBufFileCommon(nfiles);
 	file->files = files;
@@ -793,20 +794,26 @@ BufFileTellBlock(BufFile *file)
 #endif
 
 /*
- * Return the current file size.
+ * Return the current shared BufFile size.
  *
  * Counts any holes left behind by BufFileAppend as part of the size.
- * Returns -1 on error.
+ * ereport()s on failure.
  */
 int64
 BufFileSize(BufFile *file)
 {
 	int64		lastFileSize;
 
+	Assert(file->fileset != NULL);
+
 	/* Get the size of the last physical file by seeking to end. */
 	lastFileSize = FileSeek(file->files[file->numFiles - 1], 0, SEEK_END);
 	if (lastFileSize < 0)
-		return -1;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not determine size of temporary file \"%s\" from BufFile \"%s\": %m",
+						FilePathName(file->files[file->numFiles - 1]),
+						file->name)));
 	file->offsets[file->numFiles - 1] = lastFileSize;
 
 	return ((file->numFiles - 1) * (int64) MAX_PHYSICAL_FILESIZE) +
diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
@@ -433,10 +433,6 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
 		pg_itoa(i, filename);
 		file = BufFileOpenShared(fileset, filename);
 		filesize = BufFileSize(file);
-		if (filesize < 0)
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not determine size of temporary file \"%s\"", filename)));
 
 		/*
 		 * Stash first BufFile, and concatenate subsequent BufFiles to that.
