[CRIU] [PATCH 3/3] fsnotify: inotify -- Add flushing of criu generated events

[Cyrill Gorcunov]

When we restore inotify events we generate own events. So flush them before
restored application get control back, otherwise the application may get
confused because these events has nothing to do with original application
logic.

Note at the moment we call the inotify_flush_events without testing
if the descriptor is created with O_NONBLOCK, that's because we know
that we're generating events. But this might be not always true so
be prepared.

Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
---
 fsnotify.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

diff --git a/fsnotify.c b/fsnotify.c
index c14ecb4d6225..08d39e5f24f9 100644
--- a/fsnotify.c
+++ b/fsnotify.c
@@ -403,6 +403,86 @@ err:
 	return path;
 }
 
+static void decode_event_mask(char *buf, size_t size, u32 mask)
+{
+	static const char *names[32] = {
+		[ 0]	= "IN_ACCESS",
+		[ 1]	= "IN_MODIFY",
+		[ 2]	= "IN_ATTRIB",
+		[ 3]	= "IN_CLOSE_WRITE",
+		[ 4]	= "IN_CLOSE_NOWRITE",
+		[ 5]	= "IN_OPEN",
+		[ 6]	= "IN_MOVED_FROM",
+		[ 7]	= "IN_MOVED_TO",
+		[ 8]	= "IN_CREATE",
+		[ 9]	= "IN_DELETE",
+		[10]	= "IN_DELETE_SELF",
+		[11]	= "IN_MOVE_SELF",
+
+		[13]	= "IN_UNMOUNT",
+		[14]	= "IN_Q_OVERFLOW",
+		[15]	= "IN_IGNORED",
+
+		[24]	= "IN_ONLYDIR",
+		[25]	= "IN_DONT_FOLLOW",
+		[26]	= "IN_EXCL_UNLINK",
+
+		[29]	= "IN_MASK_ADD",
+		[30]	= "IN_ISDIR",
+		[31]	= "IN_ONESHOT",
+	};
+
+	size_t i, j;
+
+	memzero(buf, size);
+	for (i = 0, j = 0; i < 32 && j < size; i++) {
+		if (!(mask & (1u << i)))
+			continue;
+		if (j)
+			j += snprintf(&buf[j], size - j, " | %s", names[i]);
+		else
+			j += snprintf(&buf[j], size - j, "%s", names[i]);
+	}
+}
+
+static int inotify_flush_events(int inotify_fd, struct fsnotify_file_info *info)
+{
+	struct inotify_event *event;
+	char buf[sizeof(*event) * 8];
+	int ret, off;
+
+	/*
+	 * NOTE: It's up to a caller to make @inotify_fd being
+	 * created with O_NONBLOCK if needed.
+	 */
+	while (1) {
+		ret = read(inotify_fd, buf, sizeof(buf));
+		if (ret < 0) {
+			if (errno != EAGAIN) {
+				pr_perror("Can't read inotify queue for 0x%08x",
+					  info->ife->id);
+				return -1;
+			} else
+				return 0;
+		} else if (ret <= 0)
+			break;
+
+		if (pr_quelled(LOG_DEBUG))
+			continue;
+
+		for (off = 0; off < ret; off += sizeof(*event) + event->len) {
+			char emask[128];
+
+			event = (void *)(buf + off);
+			decode_event_mask(emask, sizeof(emask), event->mask);
+			pr_debug("\t0x%08x: flushing event %#10x -> %s\n",
+				 info->ife->id, event->mask, emask);
+		}
+	}
+
+	return ret;
+}
+
 static int restore_one_inotify(int inotify_fd, struct fsnotify_mark_info *info)
 {
 	InotifyWdEntry *iwe = info->iwe;
@@ -539,6 +619,14 @@ static int open_inotify_fd(struct file_desc *d)
 	if (restore_fown(tmp, info->ife->fown))
 		close_safe(&tmp);
 
+	if (tmp >= 0) {
+		if (!list_empty(&info->marks)) {
+			if (inotify_flush_events(tmp, info)) {
+				pr_err("Can't flush event queue for 0x%08x", info->ife->id);
+				close_safe(&tmp);
+			}
+		}
+	}
 	return tmp;
 }
 
-- 
1.9.3