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[PATCH] Manual should discourage mixing TEMP_FAILURE_RETRY and close

From:  Mark Mentovai <mark-AT-chromium.org>
To:  libc-alpha-AT-sourceware.org
Subject:  [PATCH] Manual should discourage mixing TEMP_FAILURE_RETRY and close
Date:  Tue, 3 Dec 2013 13:05:21 -0500 (EST)
Message-ID:  <alpine.OSX.2.00.1312031258470.48895@cougar>
Archive-link:  Article

When the close system call is interrupted by a signal, the state of its
file descriptor argument is not specified[1]. On Linux, a close that
fails with EINTR must not be restarted because the file descriptor is
guaranteed to have been closed at that point[2]. Note that the kernel
itself never restarts a close when SA_RESTART is set or when no
user-space signal handler is present[3].

Because glibc is widely used on Linux, its documentation should state
affirmatively that the TEMP_FAILURE_RETRY, which restarts interrupted
system calls that fail with EINTR, is not to be used with close on
Linux. Examples in glibc documentation should avoid recommending
wrapping close with TEMP_FAILURE_RETRY.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions...
[2] http://lkml.org/lkml/2005/9/10/129
[3]
http://git.kernel.org/cgit/linux/kernel/git/stable/linux-...

2013-12-03  Mark Mentovai  <mark@chromium.org>

	* manual/llio.texi (Opening and Closing Files): Document that
	TEMP_FAILURE_RETRY should not be used with close on Linux.
	(Duplicating Descriptors): Don't wrap close in TEMP_FAILURE_RETRY
	in example code.

---
 manual/llio.texi | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/manual/llio.texi b/manual/llio.texi
index b6c9260..f04a2cf 100644
--- a/manual/llio.texi
+++ b/manual/llio.texi
@@ -253,11 +253,9 @@ The @var{filedes} argument is not a valid file descriptor.
 @item EINTR
 The @code{close} call was interrupted by a signal.
 @xref{Interrupted Primitives}.
-Here is an example of how to handle @code{EINTR} properly:
-
-@smallexample
-TEMP_FAILURE_RETRY (close (desc));
-@end smallexample
+On Linux, @code{close} will have closed its file descriptor argument even when
+reporting @code{EINTR}.  It is not safe to retry calling @code{close} in this
+case, as would be done when wrapped in the @code{TEMP_FAILURE_RETRY} macro.
 
 @item ENOSPC
 @itemx EIO
@@ -2765,7 +2763,7 @@ if (pid == 0)
     @dots{}
     file = TEMP_FAILURE_RETRY (open (filename, O_RDONLY));
     dup2 (file, STDIN_FILENO);
-    TEMP_FAILURE_RETRY (close (file));
+    close (file);
     execv (program, NULL);
   @}
 @end smallexample
-- 
1.8.3.4



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