From 0cb628dfe2980b45fb7db5edd2f197d23905b02e Mon Sep 17 00:00:00 2001
From: "Bryn M. Reeves" <bmr@redhat.com>
Date: Wed, 7 Jun 2017 19:26:09 +0100
Subject: [PATCH] dmfilemapd: update file block count at daemon start

The file block count stored in the filemap_monitor was lazily
initialised at the time of the first check. This causes problems
in the case that the file has been truncated between this time and
the time the daemon started: the initial block count and current
block count match and the daemon fails to detect a change.

Separate the setting of the block count from the check and make a
call to update the value at the start of _dmfilemapd().
---
 daemons/dmfilemapd/dmfilemapd.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/daemons/dmfilemapd/dmfilemapd.c b/daemons/dmfilemapd/dmfilemapd.c
index 2637bd299..0dbdefc5b 100644
--- a/daemons/dmfilemapd/dmfilemapd.c
+++ b/daemons/dmfilemapd/dmfilemapd.c
@@ -357,30 +357,33 @@ static int _parse_args(int argc, char **argv, struct filemap_monitor *fm)
 	return 1;
 }
 
-static int _filemap_fd_check_changed(struct filemap_monitor *fm)
+static int _filemap_fd_update_blocks(struct filemap_monitor *fm)
 {
-	int64_t blocks, old_blocks;
 	struct stat buf;
 
 	if (fm->fd < 0) {
 		log_error("Filemap fd is not open.");
-		return -1;
+		return 0;
 	}
 
 	if (fstat(fm->fd, &buf)) {
 		log_error("Failed to fstat filemap file descriptor.");
-		return -1;
+		return 0;
 	}
 
-	blocks = buf.st_blocks;
+	fm->blocks = buf.st_blocks;
 
-	/* first check? */
-	if (fm->blocks < 0)
-		old_blocks = buf.st_blocks;
-	else
-		old_blocks = fm->blocks;
+	return 1;
+}
 
-	fm->blocks = blocks;
+static int _filemap_fd_check_changed(struct filemap_monitor *fm)
+{
+	int64_t old_blocks;
+
+	old_blocks = fm->blocks;
+
+	if (!_filemap_fd_update_blocks(fm))
+		return -1;
 
 	return (fm->blocks != old_blocks);
 }
@@ -714,6 +717,9 @@ static int _dmfilemapd(struct filemap_monitor *fm)
 	if (!_filemap_monitor_set_notify(fm))
 		goto bad;
 
+	if (!_filemap_fd_update_blocks(fm))
+		goto bad;
+
 	if (!dm_stats_list(dms, DM_STATS_ALL_PROGRAMS)) {
 		log_error("Failed to list stats handle.");
 		goto bad;