[PATCH 2/2] run-command: handle short writes and EINTR in die_child

[Jonathan Nieder <jrnieder@gmail.com>]

If start_command fails after forking and before exec finishes, there
is not much use in noticing an I/O error on top of that.
finish_command will notice that the child exited with nonzero status
anyway.  So as noted in v1.7.0.3~20^2 (run-command.c: fix build
warnings on Ubuntu, 2010-01-30) and v1.7.5-rc0~29^2 (2011-03-16), it
is safe to ignore errors from write in this codepath.

Even so, the result from write contains useful information: it tells
us if the write was cancelled by a signal (EINTR) or was only
partially completed (e.g., when writing to an almost-full pipe).
Let's use write_in_full to loop until the desired number of bytes have
been written (still ignoring errors if that fails).

As a happy side effect, the assignment to a dummy variable to appease
gcc -D_FORTIFY_SOURCE is no longer needed.  xwrite and write_in_full
check the return value from write(2).

Noticed with gcc -Wunused-but-set-variable.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
Changes from v1:

 - rewrite the commit message from the pov of a person who does not
   care about this patch's origin as a brown paper bag

 - drop the "if"s.  If the fussy compiler/library combination was
   right in some strange sense after all, then it does not make much
   sense to take the opportunity to make another token effort to
   appease it as a preventative step.

 run-command.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/run-command.c b/run-command.c
index f91e446..70e8a24 100644
--- a/run-command.c
+++ b/run-command.c
@@ -67,21 +67,24 @@ static int child_notifier = -1;
 
 static void notify_parent(void)
 {
-	ssize_t unused;
-	unused = write(child_notifier, "", 1);
+	/*
+	 * execvp failed.  If possible, we'd like to let start_command
+	 * know, so failures like ENOENT can be handled right away; but
+	 * otherwise, finish_command will still report the error.
+	 */
+	xwrite(child_notifier, "", 1);
 }
 
 static NORETURN void die_child(const char *err, va_list params)
 {
 	char msg[4096];
-	ssize_t unused;
 	int len = vsnprintf(msg, sizeof(msg), err, params);
 	if (len > sizeof(msg))
 		len = sizeof(msg);
 
-	unused = write(child_err, "fatal: ", 7);
-	unused = write(child_err, msg, len);
-	unused = write(child_err, "\n", 1);
+	write_in_full(child_err, "fatal: ", 7);
+	write_in_full(child_err, msg, len);
+	write_in_full(child_err, "\n", 1);
 	exit(128);
 }
 #endif
-- 
1.7.5.rc2