Handle ReadFile() EOF correctly on Windows.

macdice · macdice · commit 6969deeb8d39 · 2019-11-20T18:29:37.000+13:00
When ReadFile() encounters the end of a file while reading from a synchronous handle with an offset provided via OVERLAPPED, it reports an error instead of returning 0. By not handling that (undocumented) result correctly, we caused some noisy LOG messages about an unknown error code. Repair. Back-patch to 12, where we started using pread()/ReadFile() with an offset. Reported-by: ZhenHua Cai, Amit Kapila Diagnosed-by: Juan Jose Santamaria Flecha Tested-by: Amit Kapila Discussion: https://postgr.es/m/CAA4eK1LK3%2BWRtpz68TiRdpHwxxWm%3D%2Bt1BMf-G68hhQsAQ41PZg%40mail.gmail.com
diff --git a/src/port/pread.c b/src/port/pread.c
@@ -41,6 +41,9 @@ pg_pread(int fd, void *buf, size_t size, off_t offset)
 	overlapped.Offset = offset;
 	if (!ReadFile(handle, buf, size, &result, &overlapped))
 	{
+		if (GetLastError() == ERROR_HANDLE_EOF)
+			return 0;
+
 		_dosmaperr(GetLastError());
 		return -1;
 	}

Original file line number	Diff line number	Diff line change
`@@ -41,6 +41,9 @@ pg_pread(int fd, void *buf, size_t size, off_t offset)`
`41`	`41`	`overlapped.Offset = offset;`
`42`	`42`	`if (!ReadFile(handle, buf, size, &result, &overlapped))`
`43`	`43`	`{`
	`44`	`+ if (GetLastError() == ERROR_HANDLE_EOF)`
	`45`	`+ return 0;`
	`46`	`+`
`44`	`47`	`_dosmaperr(GetLastError());`
`45`	`48`	`return -1;`
`46`	`49`	`}`