On 16/01/2025 12:59, Mikulas Patocka wrote:
dm-mirror uses dm-io to perform the writes on multiple mirror legs (see
the function do_write() -> dm_io()), I looked at the code and it seems
that the support for atomic writes in dm-mirror and dm-io would be
straightforward.
I tried this out, and it seems to work ok.
However, I need to set DM_TARGET_ATOMIC_WRITES in the mirror_target.features
member, like:
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 9511dae5b556..913a92c55904 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -1485,6 +1485,7 @@ static struct target_type mirror_target = {
.name = "mirror",
.version = {1, 14, 0},
.module = THIS_MODULE,
+ .features = DM_TARGET_ATOMIC_WRITES,
.ctr = mirror_ctr,
.dtr = mirror_dtr,
.map = mirror_map,
Is this the right thing to do? I ask, as none of the other DM_TARGET* flags
are set already, which makes me suspicious.
Thanks,
John
Yes - that's right. I suggest that you verify that the atomic flag is
really passed through the dm-raid1.c and dm-io.c stack. Add a printk that
tests if REQ_ATOMIC is set to the function do_region in dm-io.c just
before "submit_bio(bio)".
Alternatively, you can use blktrace to test if the REQ_ATOMIC is passed
through correctly.
Yes, it is passed ok.
JFYI, I can also verify proper atomic write functionality on /dev/dmX
with fio in verify mode.
Thanks,
John
