On Wed, Oct 25 2023 at 5:34P -0400,
Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> On 10/26/23 00:03, Mike Snitzer wrote:
> > On Wed, Oct 25 2023 at 3:23P -0400,
> > Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> >
> >> dm-error is used in several test cases in the xfstests test suite to
> >> check the handling of IO errors in file systems. However, with several
> >> file systems getting native support for zoned block devices (e.g. btrfs
> >> and f2fs), dm-error lack of zoned block device support creates problems
> >> as the file system attempt executing zone commands (e.g. a zone append
> >> operation) against a dm-error non-zoned block device, which causes
> >> various issues in the block layer (e.g. WARN_ON triggers).
> >>
> >> This patch adds supports for zoned block devices to dm-error, allowing
> >> an error table to be exposed as a zoned block device. This is done by
> >> relying on the first argument passed to dmsetup when creating the device
> >> table: if that first argument is a path to a backing block device, the
> >> dm-error device is created by copying the limits of the backing device,
> >> thus also copying its zone model. This is consistent with how xfstests
> >> creates dm-error devices (always passing the path to the backing device
> >> as the first argument).
> >>
> >> The zone support for dm-error requires the definition of the
> >> report_zones target type method, which is done by introducing the
> >> function io_err_report_zones(). Given that this function fails report
> >> zones operations (similarly to any other command issued to the dm-error
> >> device), dm_set_zones_restrictions() is tweaked to do nothing for a
> >> wildcard target to avoid failing zone revalidation. As the dm-error
> >> target does not implement the iterate_devices method,
> >> dm_table_supports_zoned_model() is also changed to return true.
> >>
> >> Signed-off-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
> >> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> >> Tested-by: Christoph Hellwig <hch@xxxxxx>
> >> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> >> ---
> >> Changes from v1:
> >> - Improved comment in io_err_ctr() about error from dm_get_device()
> >> being ignored
> >> - Fixed typos in the commit message
> >> - Added review and tested-by tags
> >
> > Thanks for the improvements. But likely a v3 is worthwhile.
> >
> > Comment inlined below.
> >
> >>
> >> drivers/md/dm-table.c | 3 +++
> >> drivers/md/dm-target.c | 45 ++++++++++++++++++++++++++++++++++++++++--
> >> drivers/md/dm-zone.c | 9 +++++++++
> >> 3 files changed, 55 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> >> index 37b48f63ae6a..5e4d887063d3 100644
> >> --- a/drivers/md/dm-table.c
> >> +++ b/drivers/md/dm-table.c
> >> @@ -1600,6 +1600,9 @@ static bool dm_table_supports_zoned_model(struct dm_table *t,
> >> for (unsigned int i = 0; i < t->num_targets; i++) {
> >> struct dm_target *ti = dm_table_get_target(t, i);
> >>
> >> + if (dm_target_is_wildcard(ti->type))
> >> + continue;
> >> +
> >> if (dm_target_supports_zoned_hm(ti->type)) {
> >> if (!ti->type->iterate_devices ||
> >> ti->type->iterate_devices(ti, device_not_zoned_model,
> >> diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
> >> index 27e2992ff249..fcb2ba2bffa2 100644
> >> --- a/drivers/md/dm-target.c
> >> +++ b/drivers/md/dm-target.c
> >> @@ -118,6 +118,24 @@ EXPORT_SYMBOL(dm_unregister_target);
> >> */
> >> static int io_err_ctr(struct dm_target *tt, unsigned int argc, char **args)
> >> {
> >> + struct dm_dev *ddev;
> >> + int ret;
> >> +
> >> + /*
> >> + * If we have an argument, assume it is the path to the backing
> >> + * block device that we are replacing. In this case, get the device
> >> + * so that we can copy its limits in io_err_io_hints(). If getting the
> >> + * device fails (e.g. because the user did not specify a device file
> >> + * path), ignore the error to be compatible with the normal use case
> >> + * without any argument specified.
> >> + */
> >> + if (argc) {
> >> + ret = dm_get_device(tt, args[0], dm_table_get_mode(tt->table),
> >> + &ddev);
> >> + if (ret == 0)
> >> + tt->private = ddev;
> >> + }
> >> +
> >> /*
> >> * Return error for discards instead of -EOPNOTSUPP
> >> */
> >>
> >> @@ -129,7 +147,10 @@ static int io_err_ctr(struct dm_target *tt, unsigned int argc, char **args)
> >>
> >> static void io_err_dtr(struct dm_target *tt)
> >> {
> >> - /* empty */
> >> + struct dm_dev *ddev = tt->private;
> >> +
> >> + if (ddev)
> >> + dm_put_device(tt, ddev);
> >> }
> >>
> >> static int io_err_map(struct dm_target *tt, struct bio *bio)
> >> @@ -149,8 +170,27 @@ static void io_err_release_clone_rq(struct request *clone,
> >> {
> >> }
> >>
> >> +#ifdef CONFIG_BLK_DEV_ZONED
> >> +static int io_err_report_zones(struct dm_target *ti,
> >> + struct dm_report_zones_args *args, unsigned int nr_zones)
> >> +{
> >> + return -EIO;
> >> +}
> >> +#else
> >> +#define io_err_report_zones NULL
> >> +#endif
> >> +
> >> static void io_err_io_hints(struct dm_target *ti, struct queue_limits *limits)
> >> {
> >> + struct dm_dev *ddev = ti->private;
> >> +
> >> + /* If we have a target device, copy its limits */
> >> + if (ddev) {
> >> + struct request_queue *q = bdev_get_queue(ddev->bdev);
> >> +
> >> + memcpy(limits, &q->limits, sizeof(*limits));
> >> + }
> >> +
> >> limits->max_discard_sectors = UINT_MAX;
> >> limits->max_hw_discard_sectors = UINT_MAX;
> >> limits->discard_granularity = 512;
> >
> >
> > You don't need to explicitly copy the queue_limits, DM core
> > (dm-table.c:dm_calculate_queue_limits) will stack up the underlying
> > device's queue_limits as long as you implement io_err_iterate_devices
> > (like dm-linear.c:linear_iterate_devices).
> >
> > With io_err_iterate_devices you shouldn't need to change
> > io_err_io_hints -- but actually I could see there being a need to wrap
> > setting the above no-device defaults only if (!ddev).. or:
> > if (ddev)
> > return;
>
> Works for me, but I do not see how iterate_devices would work if there is no
> backing device specified (current default). Am I missing something ?
You don't call 'fn' if the ddev (ti->private) is NULL.
> Also,
> doesn't adding the iterate_devices method allow combining dm-error with other dm
> targets in the same table, something that is not possible currently ? So that
> would change dm-error usage. OK with me, but I want to make sure.
No, iterate_devices is purely for iterating within a given target's
devices to call the provide 'fn'.
What I suggested doesn't change combining dm-error with other targets
in the same table. But we do allow that, think of a table with
multiple linear targets and a subset that is the error target.
> But it may be that I am missing something because of the wildcard flag. Is do
> not fully understand how that one impacts anything. Is that flag responsible for
> preventing dm-error to be combined with other targets ?
/*
* Indicates that a target may replace any target; even immutable targets.
* .map, .map_rq, .clone_and_map_rq and .release_clone_rq are all defined.
*/
#define DM_TARGET_WILDCARD 0x00000008
Just means that the error target can replace all types of DM targets
(its the only DM target that sets the DM_TARGET_WILDCARD flag).
Mike
