This is the 1/4 patch to support device-replace on zoned filesystems.

We have two types of I/Os during the device-replace process. One is an I/O
to "copy" (by the scrub functions) all the device extents from the source
device to the destination device. The other one is an I/O to "clone" (by
handle_ops_on_dev_replace()) new incoming write I/Os from users to the
source device into the target device.

Cloning incoming I/Os can break the sequential write rule in on target
device. When a write is mapped in the middle of a block group, the I/O is
directed to the middle of a target device zone, which breaks the
sequential write requirement.

However, the cloning function cannot be disabled since incoming I/Os
targeting already copied device extents must be cloned so that the I/O is
executed on the target device.

We cannot use dev_replace->cursor_{left,right} to determine whether a bio
is going to a not yet copied region. Since we have a time gap between
finishing btrfs_scrub_dev() and rewriting the mapping tree in
btrfs_dev_replace_finishing(), we can have a newly allocated device extent
which is never cloned nor copied.

So the point is to copy only already existing device extents. This patch
introduces mark_block_group_to_copy() to mark existing block groups as a
target of copying. Then, handle_ops_on_dev_replace() and dev-replace can
check the flag to do their job.

Also, btrfs_finish_block_group_to_copy() will check if the copied stripe
is the last stripe in the block group. With the last stripe copied,
the to_copy flag is finally disabled. Afterwards we can safely clone
incoming IOs on this block group.

Reviewed-by: Josef Bacik <jo...@toxicpanda.com>
Signed-off-by: Naohiro Aota <naohiro.a...@wdc.com>
---
 fs/btrfs/block-group.h |   1 +
 fs/btrfs/dev-replace.c | 184 +++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/dev-replace.h |   3 +
 fs/btrfs/scrub.c       |  16 ++++
 4 files changed, 204 insertions(+)

diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index a07108d65c44..d37ee576ac6e 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -95,6 +95,7 @@ struct btrfs_block_group {
        unsigned int iref:1;
        unsigned int has_caching_ctl:1;
        unsigned int removed:1;
+       unsigned int to_copy:1;
 
        int disk_cache_state;
 
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index bc73f798ce3a..3a9c1e046ebe 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -22,6 +22,7 @@
 #include "dev-replace.h"
 #include "sysfs.h"
 #include "zoned.h"
+#include "block-group.h"
 
 /*
  * Device replace overview
@@ -459,6 +460,185 @@ static char* btrfs_dev_name(struct btrfs_device *device)
                return rcu_str_deref(device->name);
 }
 
+static int mark_block_group_to_copy(struct btrfs_fs_info *fs_info,
+                                   struct btrfs_device *src_dev)
+{
+       struct btrfs_path *path;
+       struct btrfs_key key;
+       struct btrfs_key found_key;
+       struct btrfs_root *root = fs_info->dev_root;
+       struct btrfs_dev_extent *dev_extent = NULL;
+       struct btrfs_block_group *cache;
+       struct btrfs_trans_handle *trans;
+       int ret = 0;
+       u64 chunk_offset;
+
+       /* Do not use "to_copy" on non zoned filesystem for now */
+       if (!btrfs_is_zoned(fs_info))
+               return 0;
+
+       mutex_lock(&fs_info->chunk_mutex);
+
+       /* Ensure we don't have pending new block group */
+       spin_lock(&fs_info->trans_lock);
+       while (fs_info->running_transaction &&
+              !list_empty(&fs_info->running_transaction->dev_update_list)) {
+               spin_unlock(&fs_info->trans_lock);
+               mutex_unlock(&fs_info->chunk_mutex);
+               trans = btrfs_attach_transaction(root);
+               if (IS_ERR(trans)) {
+                       ret = PTR_ERR(trans);
+                       mutex_lock(&fs_info->chunk_mutex);
+                       if (ret == -ENOENT) {
+                               spin_lock(&fs_info->trans_lock);
+                               continue;
+                       } else {
+                               goto unlock;
+                       }
+               }
+
+               ret = btrfs_commit_transaction(trans);
+               mutex_lock(&fs_info->chunk_mutex);
+               if (ret)
+                       goto unlock;
+
+               spin_lock(&fs_info->trans_lock);
+       }
+       spin_unlock(&fs_info->trans_lock);
+
+       path = btrfs_alloc_path();
+       if (!path) {
+               ret = -ENOMEM;
+               goto unlock;
+       }
+
+       path->reada = READA_FORWARD;
+       path->search_commit_root = 1;
+       path->skip_locking = 1;
+
+       key.objectid = src_dev->devid;
+       key.type = BTRFS_DEV_EXTENT_KEY;
+       key.offset = 0;
+
+       ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+       if (ret < 0)
+               goto free_path;
+       if (ret > 0) {
+               if (path->slots[0] >=
+                   btrfs_header_nritems(path->nodes[0])) {
+                       ret = btrfs_next_leaf(root, path);
+                       if (ret < 0)
+                               goto free_path;
+                       if (ret > 0) {
+                               ret = 0;
+                               goto free_path;
+                       }
+               } else {
+                       ret = 0;
+               }
+       }
+
+       while (1) {
+               struct extent_buffer *leaf = path->nodes[0];
+               int slot = path->slots[0];
+
+               btrfs_item_key_to_cpu(leaf, &found_key, slot);
+
+               if (found_key.objectid != src_dev->devid)
+                       break;
+
+               if (found_key.type != BTRFS_DEV_EXTENT_KEY)
+                       break;
+
+               if (found_key.offset < key.offset)
+                       break;
+
+               dev_extent = btrfs_item_ptr(leaf, slot, struct 
btrfs_dev_extent);
+
+               chunk_offset = btrfs_dev_extent_chunk_offset(leaf, dev_extent);
+
+               cache = btrfs_lookup_block_group(fs_info, chunk_offset);
+               if (!cache)
+                       goto skip;
+
+               spin_lock(&cache->lock);
+               cache->to_copy = 1;
+               spin_unlock(&cache->lock);
+
+               btrfs_put_block_group(cache);
+
+skip:
+               ret = btrfs_next_item(root, path);
+               if (ret != 0) {
+                       if (ret > 0)
+                               ret = 0;
+                       break;
+               }
+       }
+
+free_path:
+       btrfs_free_path(path);
+unlock:
+       mutex_unlock(&fs_info->chunk_mutex);
+
+       return ret;
+}
+
+bool btrfs_finish_block_group_to_copy(struct btrfs_device *srcdev,
+                                     struct btrfs_block_group *cache,
+                                     u64 physical)
+{
+       struct btrfs_fs_info *fs_info = cache->fs_info;
+       struct extent_map *em;
+       struct map_lookup *map;
+       u64 chunk_offset = cache->start;
+       int num_extents, cur_extent;
+       int i;
+
+       /* Do not use "to_copy" on non zoned filesystem for now */
+       if (!btrfs_is_zoned(fs_info))
+               return true;
+
+       spin_lock(&cache->lock);
+       if (cache->removed) {
+               spin_unlock(&cache->lock);
+               return true;
+       }
+       spin_unlock(&cache->lock);
+
+       em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
+       ASSERT(!IS_ERR(em));
+       map = em->map_lookup;
+
+       num_extents = cur_extent = 0;
+       for (i = 0; i < map->num_stripes; i++) {
+               /* We have more device extent to copy */
+               if (srcdev != map->stripes[i].dev)
+                       continue;
+
+               num_extents++;
+               if (physical == map->stripes[i].physical)
+                       cur_extent = i;
+       }
+
+       free_extent_map(em);
+
+       if (num_extents > 1 && cur_extent < num_extents - 1) {
+               /*
+                * Has more stripes on this device. Keep this block group
+                * readonly until we finish all the stripes.
+                */
+               return false;
+       }
+
+       /* Last stripe on this device */
+       spin_lock(&cache->lock);
+       cache->to_copy = 0;
+       spin_unlock(&cache->lock);
+
+       return true;
+}
+
 static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
                const char *tgtdev_name, u64 srcdevid, const char *srcdev_name,
                int read_src)
@@ -500,6 +680,10 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info 
*fs_info,
        if (ret)
                return ret;
 
+       ret = mark_block_group_to_copy(fs_info, src_device);
+       if (ret)
+               return ret;
+
        down_write(&dev_replace->rwsem);
        switch (dev_replace->replace_state) {
        case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
diff --git a/fs/btrfs/dev-replace.h b/fs/btrfs/dev-replace.h
index 60b70dacc299..3911049a5f23 100644
--- a/fs/btrfs/dev-replace.h
+++ b/fs/btrfs/dev-replace.h
@@ -18,5 +18,8 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info);
 void btrfs_dev_replace_suspend_for_unmount(struct btrfs_fs_info *fs_info);
 int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info);
 int __pure btrfs_dev_replace_is_ongoing(struct btrfs_dev_replace *dev_replace);
+bool btrfs_finish_block_group_to_copy(struct btrfs_device *srcdev,
+                                     struct btrfs_block_group *cache,
+                                     u64 physical);
 
 #endif
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 5f4f88a4d2c8..da4f9c24e42d 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3561,6 +3561,16 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
                if (!cache)
                        goto skip;
 
+               if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) {
+                       spin_lock(&cache->lock);
+                       if (!cache->to_copy) {
+                               spin_unlock(&cache->lock);
+                               ro_set = 0;
+                               goto done;
+                       }
+                       spin_unlock(&cache->lock);
+               }
+
                /*
                 * Make sure that while we are scrubbing the corresponding block
                 * group doesn't get its logical address and its device extents
@@ -3692,6 +3702,12 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 
                scrub_pause_off(fs_info);
 
+               if (sctx->is_dev_replace &&
+                   !btrfs_finish_block_group_to_copy(dev_replace->srcdev,
+                                                     cache, found_key.offset))
+                       ro_set = 0;
+
+done:
                down_write(&dev_replace->rwsem);
                dev_replace->cursor_left = dev_replace->cursor_right;
                dev_replace->item_needs_writeback = 1;
-- 
2.30.0

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