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[PATCH v2 6/6] Win32: fix broken pipe detection

From
Stepan Kasal <kasal@ucw.cz>
Date
Jun 7, 2014, 07:57 UTC
Message-ID
<1402127845-4862-7-git-send-email-kasal@ucw.cz>
In-Reply-To
<1402127845-4862-1-git-send-email-kasal@ucw.cz>
From: Karsten Blees <blees@dcon.de>
Date: Thu, 1 Mar 2012 21:53:54 +0100

As of "Win32: Thread-safe windows console output", git-log no longer terminates when the pager process dies. This is due to disabling buffering for the replaced stdout / stderr streams. Git-log will periodically fflush stdout (see write_or_die.c/mayble_flush_or_die()), but with no buffering, this is a NOP that always succeeds (so we never detect the EPIPE error).

Exchange the original console handles with our console thread pipe handles by accessing the internal MSVCRT data structures directly (which are exposed via __pioinfo for some reason).

Implement this with minimal assumptions about the actual data structure to make it work with different (hopefully even future) MSVCRT versions.

While messing with internal data structures is ugly, this patch solves the problem at the source instead of adding more workarounds. We no longer need the special winansi_isatty override, and the limitations documented in "Win32: Thread-safe windows console output" are gone (i.e. fdopen(1/2) returns unbuffered streams now, and isatty() for duped console file descriptors works as expected).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
---
 compat/mingw.h   |   2 -
 compat/winansi.c | 114 ++++++++++++++++++++++++++++++++++---------------------
 2 files changed, 70 insertions(+), 46 deletions(-)
diff --git a/compat/mingw.h b/compat/mingw.h
index 4b638d8..8dac6f9 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -318,9 +318,7 @@ int mingw_raise(int sig);
  */
 
 void winansi_init(void);
-int winansi_isatty(int fd);
 HANDLE winansi_get_osfhandle(int fd);
-#define isatty winansi_isatty
 
 /*
  * git specific compatibility
diff --git a/compat/winansi.c b/compat/winansi.c
index fcdd6dc..f96d5c2 100644
--- a/compat/winansi.c
+++ b/compat/winansi.c
@@ -8,11 +8,6 @@
 #include <winreg.h>
 
 /*
- Functions to be wrapped:
-*/
-#undef isatty
-
-/*
  ANSI codes used by git: m, K
 
  This file is git-specific. Therefore, this file does not attempt
@@ -104,6 +99,7 @@ static int is_console(int fd)
 
 	/* initialize attributes */
 	if (!initialized) {
+		console = hcon;
 		attr = plain_attr = sbi.wAttributes;
 		negative = 0;
 		initialized = 1;
@@ -465,29 +461,80 @@ static HANDLE duplicate_handle(HANDLE hnd)
 	return hresult;
 }
 
-static HANDLE redirect_console(FILE *stream, HANDLE *phcon, int new_fd)
-{
-	/* get original console handle */
-	int fd = _fileno(stream);
-	HANDLE hcon = (HANDLE) _get_osfhandle(fd);
-	if (hcon == INVALID_HANDLE_VALUE)
-		die_errno("_get_osfhandle(%i) failed", fd);
 
-	/* save a copy to phcon and console (used by the background thread) */
-	console = *phcon = duplicate_handle(hcon);
+/*
+ * Make MSVCRT's internal file descriptor control structure accessible
+ * so that we can tweak OS handles and flags directly (we need MSVCRT
+ * to treat our pipe handle as if it were a console).
+ *
+ * We assume that the ioinfo structure (exposed by MSVCRT.dll via
+ * __pioinfo) starts with the OS handle and the flags. The exact size
+ * varies between MSVCRT versions, so we try different sizes until
+ * toggling the FDEV bit of _pioinfo(1)->osflags is reflected in
+ * isatty(1).
+ */
+typedef struct {
+	HANDLE osfhnd;
+	char osflags;
+} ioinfo;
+
+extern __declspec(dllimport) ioinfo *__pioinfo[];
 
-	/* duplicate new_fd over fd (closes fd and associated handle (hcon)) */
-	if (_dup2(new_fd, fd))
-		die_errno("_dup2(%i, %i) failed", new_fd, fd);
+static size_t sizeof_ioinfo = 0;
 
-	/* no buffering, or stdout / stderr will be out of sync */
-	setbuf(stream, NULL);
-	return (HANDLE) _get_osfhandle(fd);
+#define IOINFO_L2E 5
+#define IOINFO_ARRAY_ELTS (1 << IOINFO_L2E)
+
+#define FDEV  0x40
+
+static inline ioinfo* _pioinfo(int fd)
+{
+	return (ioinfo*)((char*)__pioinfo[fd >> IOINFO_L2E] +
+			(fd & (IOINFO_ARRAY_ELTS - 1)) * sizeof_ioinfo);
+}
+
+static int init_sizeof_ioinfo()
+{
+	int istty, wastty;
+	/* don't init twice */
+	if (sizeof_ioinfo)
+		return sizeof_ioinfo >= 256;
+
+	sizeof_ioinfo = sizeof(ioinfo);
+	wastty = isatty(1);
+	while (sizeof_ioinfo < 256) {
+		/* toggle FDEV flag, check isatty, then toggle back */
+		_pioinfo(1)->osflags ^= FDEV;
+		istty = isatty(1);
+		_pioinfo(1)->osflags ^= FDEV;
+		/* return if we found the correct size */
+		if (istty != wastty)
+			return 0;
+		sizeof_ioinfo += sizeof(void*);
+	}
+	error("Tweaking file descriptors doesn't work with this MSVCRT.dll");
+	return 1;
+}
+
+static HANDLE swap_osfhnd(int fd, HANDLE new_handle)
+{
+	ioinfo *pioinfo;
+	HANDLE old_handle;
+
+	/* init ioinfo size if we haven't done so */
+	if (init_sizeof_ioinfo())
+		return INVALID_HANDLE_VALUE;
+
+	/* get ioinfo pointer and change the handles */
+	pioinfo = _pioinfo(fd);
+	old_handle = pioinfo->osfhnd;
+	pioinfo->osfhnd = new_handle;
+	return old_handle;
 }
 
 void winansi_init(void)
 {
-	int con1, con2, hwrite_fd;
+	int con1, con2;
 	char name[32];
 
 	/* check if either stdout or stderr is a console output screen buffer */
@@ -516,19 +563,11 @@ void winansi_init(void)
 	if (atexit(winansi_exit))
 		die_errno("atexit(winansi_exit) failed");
 
-	/* create a file descriptor for the write end of the pipe */
-	hwrite_fd = _open_osfhandle((long) duplicate_handle(hwrite), _O_BINARY);
-	if (hwrite_fd == -1)
-		die_errno("_open_osfhandle(%li) failed", (long) hwrite);
-
 	/* redirect stdout / stderr to the pipe */
 	if (con1)
-		hwrite1 = redirect_console(stdout, &hconsole1, hwrite_fd);
+		hconsole1 = swap_osfhnd(1, hwrite1 = duplicate_handle(hwrite));
 	if (con2)
-		hwrite2 = redirect_console(stderr, &hconsole2, hwrite_fd);
-
-	/* close pipe file descriptor (also closes the duped hwrite) */
-	close(hwrite_fd);
+		hconsole2 = swap_osfhnd(2, hwrite2 = duplicate_handle(hwrite));
 }
 
 static int is_same_handle(HANDLE hnd, int fd)
@@ -537,19 +576,6 @@ static int is_same_handle(HANDLE hnd, int fd)
 }
 
 /*
- * Return true if stdout / stderr is a pipe redirecting to the console.
- */
-int winansi_isatty(int fd)
-{
-	if (fd == 1 && is_same_handle(hwrite1, 1))
-		return 1;
-	else if (fd == 2 && is_same_handle(hwrite2, 2))
-		return 1;
-	else
-		return isatty(fd);
-}
-
-/*
  * Returns the real console handle if stdout / stderr is a pipe redirecting
  * to the console. Allows spawn / exec to pass the console to the next process.
  */

-- 
2.0.0.9635.g0be03cb

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Previous: Karsten BleesNext: Stepan Kasal
Message 21 of 22 in “First part of Unicode console support for msysgit”
  1. 0/5 First part of Unicode console support for msysgitStepan Kasal, Jun 6, 2014
  2. 1/5 Support Unicode console output on WindowsStepan Kasal, Jun 6, 2014
  3. 2/5 Detect console streams more reliably on WindowsStepan Kasal, Jun 6, 2014
  4. 3/5 Warn if the Windows console font doesn't support UnicodeStepan Kasal, Jun 6, 2014
  5. Peter KreftingJun 6, 2014
  6. Stepan KasalJun 7, 2014
  7. 4/5 Win32: move main macro to a functionStepan Kasal, Jun 6, 2014
  8. 5/5 Win32: Thread-safe windows console outputStepan Kasal, Jun 6, 2014
  9. Peter KreftingJun 6, 2014
  10. Karsten BleesJun 6, 2014
  11. Karsten BleesJun 6, 2014
  12. Stepan KasalJun 6, 2014
  13. 0/6 First part of Unicode console support for msysgitStepan Kasal, Jun 7, 2014
  14. 1/6 Support Unicode console output on WindowsStepan Kasal, Jun 7, 2014
  15. 2/6 Detect console streams more reliably on WindowsStepan Kasal, Jun 7, 2014
  16. 3/6 Warn if the Windows console font doesn't support UnicodeStepan Kasal, Jun 7, 2014
  17. 4/6 Win32: add Unicode conversion functionsStepan Kasal, Jun 7, 2014
  18. 5/6 Win32: Thread-safe windows console outputStepan Kasal, Jun 7, 2014
  19. Johannes SixtJun 13, 2014
  20. 7/6 Win32: reliably detect console pipe handlesKarsten Blees, Jun 13, 2014
  21. 6/6 Win32: fix broken pipe detectionStepan Kasal, Jun 7, 2014
  22. Stepan KasalJun 6, 2014

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