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 ? 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.
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 ?
>
> Mike
>
--
Damien Le Moal
Western Digital Research
