[dm-devel] [PATCH v6 2/4] block: add blk_interposer
Sergei Shtepa
sergei.shtepa at veeam.com
Wed Mar 3 12:30:16 UTC 2021
blk_interposer allows to intercept bio requests, remap bio
to another devices or add new bios.
Signed-off-by: Sergei Shtepa <sergei.shtepa at veeam.com>
---
block/bio.c | 2 +
block/blk-core.c | 36 +++++++++++++++
block/genhd.c | 93 +++++++++++++++++++++++++++++++++++++++
include/linux/blk_types.h | 4 ++
include/linux/blkdev.h | 17 +++++++
5 files changed, 152 insertions(+)
diff --git a/block/bio.c b/block/bio.c
index a1c4d2900c7a..0bfbf06475ee 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -640,6 +640,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
bio_set_flag(bio, BIO_THROTTLED);
if (bio_flagged(bio_src, BIO_REMAPPED))
bio_set_flag(bio, BIO_REMAPPED);
+ if (bio_flagged(bio_src, BIO_INTERPOSED))
+ bio_set_flag(bio, BIO_INTERPOSED);
bio->bi_opf = bio_src->bi_opf;
bio->bi_ioprio = bio_src->bi_ioprio;
bio->bi_write_hint = bio_src->bi_write_hint;
diff --git a/block/blk-core.c b/block/blk-core.c
index fc60ff208497..e749507cadd3 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1018,6 +1018,34 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
return ret;
}
+static blk_qc_t __submit_bio_interposed(struct bio *bio)
+{
+ struct bio_list bio_list[2] = { };
+ blk_qc_t ret = BLK_QC_T_NONE;
+
+ current->bio_list = bio_list;
+ if (likely(bio_queue_enter(bio) == 0)) {
+ struct block_device *bdev = bio->bi_bdev;
+
+ if (likely(bdev_has_interposer(bdev))) {
+ bio_set_flag(bio, BIO_INTERPOSED);
+ bdev->bd_interposer->ip_submit_bio(bio);
+ } else {
+ /* interposer was removed */
+ bio_list_add(¤t->bio_list[0], bio);
+ }
+
+ blk_queue_exit(bdev->bd_disk->queue);
+ }
+ current->bio_list = NULL;
+
+ /* Resubmit remaining bios */
+ while ((bio = bio_list_pop(&bio_list[0])))
+ ret = submit_bio_noacct(bio);
+
+ return ret;
+}
+
/**
* submit_bio_noacct - re-submit a bio to the block device layer for I/O
* @bio: The bio describing the location in memory and on the device.
@@ -1043,6 +1071,14 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
return BLK_QC_T_NONE;
}
+ /*
+ * Checking the BIO_INTERPOSED flag is necessary so that the bio
+ * created by the bdev_interposer do not get to it for processing.
+ */
+ if (bdev_has_interposer(bio->bi_bdev) &&
+ !bio_flagged(bio, BIO_INTERPOSED))
+ return __submit_bio_interposed(bio);
+
if (!bio->bi_bdev->bd_disk->fops->submit_bio)
return __submit_bio_noacct_mq(bio);
return __submit_bio_noacct(bio);
diff --git a/block/genhd.c b/block/genhd.c
index fcc530164b5a..1ae8516643c8 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -30,6 +30,11 @@
static struct kobject *block_depr;
DECLARE_RWSEM(bdev_lookup_sem);
+/*
+ * Prevents different block-layer interposers from attaching or detaching
+ * to the block device at the same time.
+ */
+DEFINE_MUTEX(bdev_interposer_attach_lock);
/* for extended dynamic devt allocation, currently only one major is used */
#define NR_EXT_DEVT (1 << MINORBITS)
@@ -1941,3 +1946,91 @@ static void disk_release_events(struct gendisk *disk)
WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
kfree(disk->ev);
}
+
+/**
+ * bdev_interposer_attach - Attach interposer to block device
+ * @bdev: target block device
+ * @interposer: block device interposer
+ * @ip_submit_bio: hook for submit_bio()
+ *
+ * Returns:
+ * -EINVAL if @interposer is NULL.
+ * -EPERM if queue is not frozen.
+ * -EBUSY if the block device already has @interposer.
+ * -EALREADY if the block device already has @interposer with same callback.
+ * -ENODEV if the block device cannot be referenced.
+ *
+ * Disk must be frozen by blk_mq_freeze_queue().
+ */
+int bdev_interposer_attach(struct block_device *bdev, struct bdev_interposer *interposer,
+ const ip_submit_bio_t ip_submit_bio)
+{
+ int ret = 0;
+
+ if (WARN_ON(!interposer))
+ return -EINVAL;
+
+ if (!blk_mq_is_queue_frozen(bdev->bd_disk->queue))
+ return -EPERM;
+
+ mutex_lock(&bdev_interposer_attach_lock);
+ if (bdev_has_interposer(bdev)) {
+ if (bdev->bd_interposer->ip_submit_bio == ip_submit_bio)
+ ret = -EALREADY;
+ else
+ ret = -EBUSY;
+ goto out;
+ }
+
+ interposer->ip_submit_bio = ip_submit_bio;
+
+ interposer->bdev = bdgrab(bdev);
+ if (!interposer->bdev) {
+ ret = -ENODEV;
+ goto out;
+ }
+
+ bdev->bd_interposer = interposer;
+out:
+ mutex_unlock(&bdev_interposer_attach_lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(bdev_interposer_attach);
+
+/**
+ * bdev_interposer_detach - Detach interposer from block device
+ * @interposer: block device interposer
+ * @ip_submit_bio: hook for submit_bio()
+ *
+ * Disk must be frozen by blk_mq_freeze_queue().
+ */
+void bdev_interposer_detach(struct bdev_interposer *interposer,
+ const ip_submit_bio_t ip_submit_bio)
+{
+ struct block_device *bdev;
+
+ if (WARN_ON(!interposer))
+ return;
+
+ mutex_lock(&bdev_interposer_attach_lock);
+
+ /* Check if the interposer is still active. */
+ bdev = interposer->bdev;
+ if (WARN_ON(!bdev))
+ goto out;
+
+ if (WARN_ON(!blk_mq_is_queue_frozen(bdev->bd_disk->queue)))
+ goto out;
+
+ /* Check if it is really our interposer. */
+ if (WARN_ON(bdev->bd_interposer->ip_submit_bio != ip_submit_bio))
+ goto out;
+
+ bdev->bd_interposer = NULL;
+ interposer->bdev = NULL;
+ bdput(bdev);
+out:
+ mutex_unlock(&bdev_interposer_attach_lock);
+}
+EXPORT_SYMBOL_GPL(bdev_interposer_detach);
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index db026b6ec15a..2b43f65bb356 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -19,6 +19,7 @@ struct io_context;
struct cgroup_subsys_state;
typedef void (bio_end_io_t) (struct bio *);
struct bio_crypt_ctx;
+struct bdev_interposer;
struct block_device {
sector_t bd_start_sect;
@@ -46,6 +47,7 @@ struct block_device {
spinlock_t bd_size_lock; /* for bd_inode->i_size updates */
struct gendisk * bd_disk;
struct backing_dev_info *bd_bdi;
+ struct bdev_interposer * bd_interposer;
/* The counter of freeze processes */
int bd_fsfreeze_count;
@@ -304,6 +306,8 @@ enum {
BIO_CGROUP_ACCT, /* has been accounted to a cgroup */
BIO_TRACKED, /* set if bio goes through the rq_qos path */
BIO_REMAPPED,
+ BIO_INTERPOSED, /* bio has been interposed and can be moved to
+ * a different block device */
BIO_FLAG_LAST
};
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c032cfe133c7..82f8515fa3c8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -2033,4 +2033,21 @@ int fsync_bdev(struct block_device *bdev);
int freeze_bdev(struct block_device *bdev);
int thaw_bdev(struct block_device *bdev);
+/*
+ * block layer interposers structure and functions
+ */
+typedef void (*ip_submit_bio_t) (struct bio *bio);
+
+struct bdev_interposer {
+ ip_submit_bio_t ip_submit_bio;
+ struct block_device *bdev;
+};
+
+#define bdev_has_interposer(bd) ((bd)->bd_interposer != NULL)
+
+int bdev_interposer_attach(struct block_device *bdev, struct bdev_interposer *interposer,
+ const ip_submit_bio_t ip_submit_bio);
+void bdev_interposer_detach(struct bdev_interposer *interposer,
+ const ip_submit_bio_t ip_submit_bio);
+
#endif /* _LINUX_BLKDEV_H */
--
2.20.1
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