[PATCH v6 4/4] dm: add DM_INTERPOSED_FLAG

From: Sergei Shtepa
Date: Wed Mar 03 2021 - 12:03:50 EST

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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.shtepa@xxxxxxxxx>
---
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);
+ }
+
+ /*
+ * Set acceptor device.
+ * It is quite convenient that device mapper creates
+ * one disk for one block device.
+ */
+ bio->bi_bdev = md->disk->part0;
+
+ /*
+ * Bio should be resubmitted.
+ * The bio will be checked again and placed in current->bio_list.
+ */
+ submit_bio_noacct(bio);
+}
+
+static int _interposer_dev_create(struct block_device *bdev, sector_t ofs, sector_t len,
+ struct mapped_device *md)
+{
+ int ret;
+
+ DMDEBUG("Create dm interposer.");
+
+ if (md->ip_dev) {
+ DMERR("The dm interposer device already in use.");
+ return -EALREADY;
+ }
+
+ 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))
+ DMDEBUG("Whole block device should be interposed.");
+
+ dm_interposer_dev_init(md->ip_dev,
+ ofs, len,
+ md, dm_interpose_fn);
+
+ ret = dm_interposer_dev_attach(bdev, md->ip_dev);
+ if (ret) {
+ DMERR("Cannot attach dm interposer device.");
+ kfree(md->ip_dev);
+ md->ip_dev = NULL;
+ }
+
+ return ret;
+}
+
+static void _interposer_dev_remove(struct block_device *bdev, struct mapped_device *md)
+{
+ if (!md->ip_dev)
+ return;
+
+ DMDEBUG("Remove dm interposer. %llu bios was interposed.",
+ atomic64_read(&md->ip_dev->ip_cnt));
+
+ if (dm_interposer_detach_dev(bdev, md->ip_dev))
+ DMERR("Failed to detach dm interposer.");
+
+ kfree(md->ip_dev);
+ md->ip_dev = NULL;
+}
+
/*
* Add a device to the list, or just increment the usage count if
* it's already present.
@@ -385,7 +471,7 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
return -ENODEV;
}

- dd = find_device(&t->devices, dev);
+ dd = find_device(&t->devices, dev, t->md->is_interposed);
if (!dd) {
dd = kmalloc(sizeof(*dd), GFP_KERNEL);
if (!dd)
@@ -398,15 +484,22 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,

refcount_set(&dd->count, 1);
list_add(&dd->list, &t->devices);
- goto out;
-
} else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
r = upgrade_mode(dd, mode, t->md);
if (r)
return r;
+ refcount_inc(&dd->count);
}
- refcount_inc(&dd->count);
-out:
+
+ if (t->md->is_interposed) {
+ r = _interposer_dev_create(dd->dm_dev->bdev, ti->begin, ti->len, t->md);
+ if (r) {
+ dm_put_device(ti, dd->dm_dev);
+ DMERR("Failed to attach dm interposer.");
+ return r;
+ }
+ }
+
*result = dd->dm_dev;
return 0;
}
@@ -446,6 +539,7 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
{
int found = 0;
struct list_head *devices = &ti->table->devices;
+ struct mapped_device *md = ti->table->md;
struct dm_dev_internal *dd;

list_for_each_entry(dd, devices, list) {
@@ -456,11 +550,14 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
}
if (!found) {
DMWARN("%s: device %s not in table devices list",
- dm_device_name(ti->table->md), d->name);
+ dm_device_name(md), d->name);
return;
}
+ if (md->is_interposed)
+ _interposer_dev_remove(d->bdev, md);
+
if (refcount_dec_and_test(&dd->count)) {
- dm_put_table_device(ti->table->md, d);
+ dm_put_table_device(md, d);
list_del(&dd->list);
kfree(dd);
}
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 50b693d776d6..466bf70a66b0 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -762,16 +762,24 @@ static int open_table_device(struct table_device *td, dev_t dev,

BUG_ON(td->dm_dev.bdev);

- bdev = blkdev_get_by_dev(dev, td->dm_dev.mode | FMODE_EXCL, _dm_claim_ptr);
- if (IS_ERR(bdev))
- return PTR_ERR(bdev);
+ if (md->is_interposed) {

- r = bd_link_disk_holder(bdev, dm_disk(md));
- if (r) {
- blkdev_put(bdev, td->dm_dev.mode | FMODE_EXCL);
- return r;
+ bdev = blkdev_get_by_dev(dev, td->dm_dev.mode, NULL);
+ if (IS_ERR(bdev))
+ return PTR_ERR(bdev);
+ } else {
+ bdev = blkdev_get_by_dev(dev, td->dm_dev.mode | FMODE_EXCL, _dm_claim_ptr);
+ if (IS_ERR(bdev))
+ return PTR_ERR(bdev);
+
+ r = bd_link_disk_holder(bdev, dm_disk(md));
+ if (r) {
+ blkdev_put(bdev, td->dm_dev.mode | FMODE_EXCL);
+ return r;
+ }
}

+ td->dm_dev.is_interposed = md->is_interposed;
td->dm_dev.bdev = bdev;
td->dm_dev.dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
return 0;
@@ -785,20 +793,26 @@ static void close_table_device(struct table_device *td, struct mapped_device *md
if (!td->dm_dev.bdev)
return;

- bd_unlink_disk_holder(td->dm_dev.bdev, dm_disk(md));
- blkdev_put(td->dm_dev.bdev, td->dm_dev.mode | FMODE_EXCL);
+ if (td->dm_dev.is_interposed)
+ blkdev_put(td->dm_dev.bdev, td->dm_dev.mode);
+ else {
+ bd_unlink_disk_holder(td->dm_dev.bdev, dm_disk(md));
+ blkdev_put(td->dm_dev.bdev, td->dm_dev.mode | FMODE_EXCL);
+ }
put_dax(td->dm_dev.dax_dev);
td->dm_dev.bdev = NULL;
td->dm_dev.dax_dev = NULL;
}

static struct table_device *find_table_device(struct list_head *l, dev_t dev,
- fmode_t mode)
+ fmode_t mode, bool is_interposed)
{
struct table_device *td;

list_for_each_entry(td, l, list)
- if (td->dm_dev.bdev->bd_dev == dev && td->dm_dev.mode == mode)
+ if (td->dm_dev.bdev->bd_dev == dev &&
+ td->dm_dev.mode == mode &&
+ td->dm_dev.is_interposed == is_interposed)
return td;

return NULL;
@@ -811,7 +825,7 @@ int dm_get_table_device(struct mapped_device *md, dev_t dev, fmode_t mode,
struct table_device *td;

mutex_lock(&md->table_devices_lock);
- td = find_table_device(&md->table_devices, dev, mode);
+ td = find_table_device(&md->table_devices, dev, mode, md->is_interposed);
if (!td) {
td = kmalloc_node(sizeof(*td), GFP_KERNEL, md->numa_node_id);
if (!td) {
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 7f4ac87c0b32..76a6dfb1cb29 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -159,6 +159,7 @@ struct dm_dev {
struct block_device *bdev;
struct dax_device *dax_dev;
fmode_t mode;
+ bool is_interposed;
char name[16];
};

diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index fcff6669137b..fc4d06bb3dbb 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -362,4 +362,10 @@ enum {
*/
#define DM_INTERNAL_SUSPEND_FLAG (1 << 18) /* Out */

+/*
+ * If set, the underlying device should open without FMODE_EXCL
+ * and attach mapped device via bdev_interposer.
+ */
+#define DM_INTERPOSED_FLAG (1 << 19) /* In */
+
#endif /* _LINUX_DM_IOCTL_H */
--
2.20.1

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