From: NeilBrown <neilb@suse.de>
Date: Sun, 22 Apr 2012 04:23:15 +0000 (+1000)
Subject: cycle_watchers: don't write the 'all done' signal until after the rename.
X-Git-Url: http://git.neil.brown.name/?a=commitdiff_plain;h=33c0bebbbf2defd40ac00941ec9c9bb4fe7ea25e;p=susman.git

cycle_watchers: don't write the 'all done' signal until after the rename.

When a suspend cycle is finished we move the new 'watching-next' into
place and we write to the old one to make sure any process watching
will notice something has happened.

It is best to write to the file *After* the rename else a process that
notices the file change might make wrong assumptions about the
then-current 'watching' file.

i.e. close a small and probably unimportant race.

Signed-off-by: NeilBrown <neilb@suse.de>
---

diff --git a/lsusd.c b/lsusd.c
index dff24f4..c9eab88 100644
--- a/lsusd.c
+++ b/lsusd.c
@@ -58,14 +58,11 @@ static void cycle_watchers(void)
 	fd = open("/var/run/suspend/watching", O_RDWR|O_CREAT, 0640);
 	if (fd < 0)
 		return;
-	zero[0] = zero[1] = 0;
-	if (write(fd, zero, 2) != 2) {
-		close(fd);
-		return;
-	}
-	close(fd);
 	rename("/var/run/suspend/watching-next",
 	       "/var/run/suspend/watching");
+	zero[0] = zero[1] = 0;
+	write(fd, zero, 2);
+	close(fd);
 }
 
 static int read_wakeup_count()