On 10/26/23 08:50, Mike Snitzer wrote:
> 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.
I was confused about that because my test script had a problem and was failing
to setup a dm-linear+dm-error combination. I now have that working and I can
check the combination.
So adding the iterate device now makes sense for the zone stuff. Will do that.
Thanks for the details. Sending a v3.
>
>> 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
>
--
Damien Le Moal
Western Digital Research
