Re: [Libguestfs] [nbdkit PATCH] cow: Always advertise multi-conn

Our cow data is locked for proper sharing across connections, so even though NBD_CMD_FLUSH is an intentional no-op, a client is guaranteed that after a flush by connection A, a read by connection B will not see any stale data, which matches the requirements for always advertising multi-conn. --- filters/cow/cow.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/filters/cow/cow.c b/filters/cow/cow.c index 93e10f24..1085ee36 100644 --- a/filters/cow/cow.c +++ b/filters/cow/cow.c @@ -181,6 +181,14 @@ cow_can_cache (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle) return NBDKIT_CACHE_NATIVE; } +static int +cow_can_multi_conn (struct nbdkit_next_ops *next_ops, void *nxdata, + void *handle) +{ + /* Our cache is consistent between connections. */ + return 1; +} + /* Override the plugin's .can_fast_zero, because our .zero is not fast */ static int cow_can_fast_zero (struct nbdkit_next_ops *next_ops, void *nxdata, @@ -712,6 +720,7 @@ static struct nbdkit_filter filter = { .can_fua = cow_can_fua, .can_cache = cow_can_cache, .can_fast_zero = cow_can_fast_zero, + .can_multi_conn = cow_can_multi_conn, .pread = cow_pread, .pwrite = cow_pwrite, .zero = cow_zero, --