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Subject[PATCH 14/17] watch_queue: sample: Display mount tree change notifications [ver #5]
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This is run like:

./watch_test

and watches "/" for changes to the mount topology and the attributes of
individual mount objects.

# mount -t tmpfs none /mnt
# mount -o remount,ro /mnt
# mount -o remount,rw /mnt

producing:

# ./watch_test
read() = 16
NOTIFY[000]: ty=000002 sy=00 i=02000010
MOUNT 00000060 change=0[new_mount] aux=416
read() = 16
NOTIFY[000]: ty=000002 sy=04 i=02010010
MOUNT 000001a0 change=4[setattr] aux=0
read() = 16
NOTIFY[000]: ty=000002 sy=04 i=02010010
MOUNT 000001a0 change=4[setattr] aux=0

Signed-off-by: David Howells <dhowells@redhat.com>
---

samples/watch_queue/watch_test.c | 44 +++++++++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c
index 46e618a897fe..36caaea5261f 100644
--- a/samples/watch_queue/watch_test.c
+++ b/samples/watch_queue/watch_test.c
@@ -26,6 +26,9 @@
#ifndef __NR_keyctl
#define __NR_keyctl -1
#endif
+#ifndef __NR_watch_mount
+#define __NR_watch_mount -1
+#endif

#define BUF_SIZE 256

@@ -58,6 +61,32 @@ static void saw_key_change(struct watch_notification *n, size_t len)
k->key_id, n->subtype, key_subtypes[n->subtype], k->aux);
}

+static const char *mount_subtypes[256] = {
+ [NOTIFY_MOUNT_NEW_MOUNT] = "new_mount",
+ [NOTIFY_MOUNT_UNMOUNT] = "unmount",
+ [NOTIFY_MOUNT_EXPIRY] = "expiry",
+ [NOTIFY_MOUNT_READONLY] = "readonly",
+ [NOTIFY_MOUNT_SETATTR] = "setattr",
+ [NOTIFY_MOUNT_MOVE_FROM] = "move_from",
+ [NOTIFY_MOUNT_MOVE_TO] = "move_to",
+};
+
+static void saw_mount_change(struct watch_notification *n, size_t len)
+{
+ struct mount_notification *m = (struct mount_notification *)n;
+
+ if (len != sizeof(struct mount_notification))
+ return;
+
+ printf("MOUNT %08x change=%u[%s] aux=%u ctr=%x,%x actr=%x\n",
+ m->triggered_on, n->subtype, mount_subtypes[n->subtype],
+ m->auxiliary_mount,
+ m->topology_changes,
+ m->attr_changes,
+ m->aux_topology_changes);
+
+}
+
/*
* Consume and display events.
*/
@@ -134,6 +163,9 @@ static void consumer(int fd)
default:
printf("other type\n");
break;
+ case WATCH_TYPE_MOUNT_NOTIFY:
+ saw_mount_change(&n.n, len);
+ break;
}

p += len;
@@ -142,12 +174,17 @@ static void consumer(int fd)
}

static struct watch_notification_filter filter = {
- .nr_filters = 1,
+ .nr_filters = 2,
.filters = {
[0] = {
.type = WATCH_TYPE_KEY_NOTIFY,
.subtype_filter[0] = UINT_MAX,
},
+ [1] = {
+ .type = WATCH_TYPE_MOUNT_NOTIFY,
+ // Reject move-from notifications
+ .subtype_filter[0] = UINT_MAX & ~(1 << NOTIFY_MOUNT_MOVE_FROM),
+ },
},
};

@@ -181,6 +218,11 @@ int main(int argc, char **argv)
exit(1);
}

+ if (syscall(__NR_watch_mount, AT_FDCWD, "/", 0, fd, 0x02) == -1) {
+ perror("watch_mount");
+ exit(1);
+ }
+
consumer(fd);
exit(0);
}

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