On Tue, May 14, 2024 at 05:04:42PM +0800, Yang Yang wrote:
> Add a list to the struct dm_dev structure to store the associated
> targets, while also allowing differentiation between different target
> types.
I still think this is more complex than it needs to be. If devices that
support flush_pass_around can guarantee that:
1. They will send a flush bio to all of their table devices
2. They are fine with another target sending the flush bio to their
table devices
Then I don't see why we need the table devices to keep track of all the
different target types that are using them. Am I missing something here?
If we don't need to worry about sending a flush bio to a target of each
type that is using a table device, then all we need to do is call
__send_empty_flush_bios() for enough targets to cover all the table
devices. This seems a lot easier to track. We just need another flag in
dm_target, something like sends_pass_around_flush.
When a target calls dm_get_device(), if it adds a new table device to
t->devices, then it's the first target in this table to use that device.
If flush_pass_around is set for this target, then it also sets
sends_pass_around_flush. In __send_empty_flush() if the table has
flush_pass_around set, when you iterate through the devices, you only
call __send_empty_flush_bios() for the ones with sends_pass_around_flush
set.
Or am I overlooking something?
-Ben
>
> Signed-off-by: Yang Yang <yang.yang@xxxxxxxx>
> ---
> drivers/md/dm-table.c | 36 +++++++++++++++++++++++++++++++++++
> include/linux/device-mapper.h | 3 +++
> 2 files changed, 39 insertions(+)
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index bd68af10afed..f6554590b7af 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -741,6 +741,8 @@ int dm_table_add_target(struct dm_table *t, const char *type,
> if (ti->flush_pass_around == 0)
> t->flush_pass_around = 0;
>
> + INIT_LIST_HEAD(&ti->list);
> +
> return 0;
>
> bad:
> @@ -2134,6 +2136,25 @@ void dm_table_postsuspend_targets(struct dm_table *t)
> suspend_targets(t, POSTSUSPEND);
> }
>
> +static int dm_link_dev_to_target(struct dm_target *ti, struct dm_dev *dev,
> + sector_t start, sector_t len, void *data)
> +{
> + struct list_head *targets = &dev->targets;
> + struct dm_target *pti;
> +
> + if (!list_empty(targets)) {
> + list_for_each_entry(pti, targets, list) {
> + if (pti->type == ti->type)
> + return 0;
> + }
> + }
> +
> + if (list_empty(&ti->list))
> + list_add_tail(&ti->list, targets);
> +
> + return 0;
> +}
> +
> int dm_table_resume_targets(struct dm_table *t)
> {
> unsigned int i;
> @@ -2162,6 +2183,21 @@ int dm_table_resume_targets(struct dm_table *t)
> ti->type->resume(ti);
> }
>
> + if (t->flush_pass_around) {
> + struct list_head *devices = &t->devices;
> + struct dm_dev_internal *dd;
> +
> + list_for_each_entry(dd, devices, list)
> + INIT_LIST_HEAD(&dd->dm_dev->targets);
> +
> + for (i = 0; i < t->num_targets; i++) {
> + struct dm_target *ti = dm_table_get_target(t, i);
> +
> + if (ti->type->iterate_devices)
> + ti->type->iterate_devices(ti, dm_link_dev_to_target, NULL);
> + }
> + }
> +
> return 0;
> }
>
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 0893ff8c01b6..19e03f9b2589 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -169,6 +169,7 @@ struct dm_dev {
> struct dax_device *dax_dev;
> blk_mode_t mode;
> char name[16];
> + struct list_head targets;
> };
>
> /*
> @@ -298,6 +299,8 @@ struct dm_target {
> struct dm_table *table;
> struct target_type *type;
>
> + struct list_head list;
> +
> /* target limits */
> sector_t begin;
> sector_t len;
> --
> 2.34.1
>
