On Wed, Mar 03, 2021 at 03:30:18PM +0300, Sergei Shtepa wrote:
> DM_INTERPOSED_FLAG allow to create dm targets on "the fly".
> Underlying block device opens without a flag FMODE_EXCL.
> Dm target receives bio from the original device via
> blk_interposer.
>
> Signed-off-by: Sergei Shtepa <sergei.sht...@veeam.com>
> ---
> drivers/md/dm-core.h | 6 ++
> drivers/md/dm-ioctl.c | 9 +++
> drivers/md/dm-table.c | 115 +++++++++++++++++++++++++++++++---
> drivers/md/dm.c | 38 +++++++----
> include/linux/device-mapper.h | 1 +
> include/uapi/linux/dm-ioctl.h | 6 ++
> 6 files changed, 154 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
> index 5953ff2bd260..e5c845f9b1df 100644
> --- a/drivers/md/dm-core.h
> +++ b/drivers/md/dm-core.h
> @@ -21,6 +21,8 @@
>
> #define DM_RESERVED_MAX_IOS 1024
>
> +struct dm_interposed_dev;
> +
> struct dm_kobject_holder {
> struct kobject kobj;
> struct completion completion;
> @@ -114,6 +116,10 @@ struct mapped_device {
> bool init_tio_pdu:1;
>
> struct srcu_struct io_barrier;
> +
> + /* for interposers logic */
> + bool is_interposed;
> + struct dm_interposed_dev *ip_dev;
> };
>
> void disable_discard(struct mapped_device *md);
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 5e306bba4375..2bcb316144a1 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1267,6 +1267,11 @@ static inline fmode_t get_mode(struct dm_ioctl *param)
> return mode;
> }
>
> +static inline bool get_interposer_flag(struct dm_ioctl *param)
> +{
> + return (param->flags & DM_INTERPOSED_FLAG);
> +}
> +
> static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
> struct dm_target_spec **spec, char **target_params)
> {
> @@ -1338,6 +1343,8 @@ static int table_load(struct file *filp, struct
> dm_ioctl *param, size_t param_si
> if (!md)
> return -ENXIO;
>
> + md->is_interposed = get_interposer_flag(param);
> +
> r = dm_table_create(&t, get_mode(param), param->target_count, md);
> if (r)
> goto err;
> @@ -2098,6 +2105,8 @@ int __init dm_early_create(struct dm_ioctl *dmi,
> if (r)
> goto err_hash_remove;
>
> + md->is_interposed = get_interposer_flag(dmi);
> +
> /* add targets */
> for (i = 0; i < dmi->target_count; i++) {
> r = dm_table_add_target(t, spec_array[i]->target_type,
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 95391f78b8d5..0b2f9b66ade5 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -6,6 +6,7 @@
> */
>
> #include "dm-core.h"
> +#include "dm-interposer.h"
>
> #include <linux/module.h>
> #include <linux/vmalloc.h>
> @@ -225,12 +226,13 @@ void dm_table_destroy(struct dm_table *t)
> /*
> * See if we've already got a device in the list.
> */
> -static struct dm_dev_internal *find_device(struct list_head *l, dev_t dev)
> +static struct dm_dev_internal *find_device(struct list_head *l, dev_t dev,
> bool is_interposed)
> {
> struct dm_dev_internal *dd;
>
> list_for_each_entry (dd, l, list)
> - if (dd->dm_dev->bdev->bd_dev == dev)
> + if ((dd->dm_dev->bdev->bd_dev == dev) &&
> + (dd->dm_dev->is_interposed == is_interposed))
> return dd;
>
> return NULL;
> @@ -358,6 +360,90 @@ dev_t dm_get_dev_t(const char *path)
> }
> EXPORT_SYMBOL_GPL(dm_get_dev_t);
>
> +/*
> + * Redirect bio from interposed device to dm device
> + */
> +static void dm_interpose_fn(struct dm_interposed_dev *ip_dev, struct bio
> *bio)
> +{
> + struct mapped_device *md = ip_dev->private;
> +
> + if (bio_flagged(bio, BIO_REMAPPED)) {
> + /*
> + * Since bio has already been remapped, we need to subtract
> + * the block device offset from the beginning of the disk.
> + */
> + bio->bi_iter.bi_sector -= get_start_sect(bio->bi_bdev);
> +
> + bio_clear_flag(bio, BIO_REMAPPED);
> + }
So instead of doing this shoudn't the imposer just always submit to the
whole device? But if we keep it, the logic in this funtion should go
into a block layer helper, passing a block device instead of the
dm_interposed_dev. This avoids having such fragile logic in drivers.
> + if ((ofs + len) > bdev_nr_sectors(bdev)) {
> + DMERR("The specified range of sectors exceeds of the size of
> the block device.");
> + return -ERANGE;
> + }
> +
> + md->ip_dev = kzalloc(sizeof(struct dm_interposed_dev), GFP_KERNEL);
> + if (!md->ip_dev)
> + return -ENOMEM;
> +
> + if ((ofs == 0) && (len == 0))
Lots of superflous inner braces.
