Re: [PATCH v2 2/7] btrfs-progs: Refactor btrfs_read_block_groups()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/10/17 上午11:23, Anand Jain wrote:
> On 10/8/19 12:49 PM, Qu Wenruo wrote:
>> This patch does the following refactor:
>> - Refactor parameter from @root to @fs_info
>>
>> - Refactor the large loop body into another function
>>    Now we have a helper function, read_one_block_group(), to handle
>>    block group cache and space info related routine.
>>
>> - Refactor the return value
>>    Even we have the code handling ret > 0 from find_first_block_group(),
>>    it never works, as when there is no more block group,
>>    find_first_block_group() just return -ENOENT other than 1.
> 
> 
>  Can it be separated into patches? My concern is as it alters the return
>  value of the rescue command. So we shall have clarity of a discrete
>  patch to blame. Otherwise I agree its a good change.

No problem.

What about 3 patches split by the mentioned 3 refactors?
> 
> 
>>    This is super confusing, it's almost a mircle it even works.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   ctree.h       |   2 +-
>>   disk-io.c     |   9 ++-
>>   extent-tree.c | 160 ++++++++++++++++++++++++++++----------------------
>>   3 files changed, 97 insertions(+), 74 deletions(-)
>>
>> diff --git a/ctree.h b/ctree.h
>> index 8c7b3cb40151..2899de358613 100644
>> --- a/ctree.h
>> +++ b/ctree.h
>> @@ -2550,7 +2550,7 @@ int update_space_info(struct btrfs_fs_info
>> *info, u64 flags,
>>                 u64 total_bytes, u64 bytes_used,
>>                 struct btrfs_space_info **space_info);
>>   int btrfs_free_block_groups(struct btrfs_fs_info *info);
>> -int btrfs_read_block_groups(struct btrfs_root *root);
>> +int btrfs_read_block_groups(struct btrfs_fs_info *info);
>>   struct btrfs_block_group_cache *
>>   btrfs_add_block_group(struct btrfs_fs_info *fs_info, u64 bytes_used,
>> u64 type,
>>                 u64 chunk_offset, u64 size);
>> diff --git a/disk-io.c b/disk-io.c
>> index be44eead5cef..8978f0cb60c7 100644
>> --- a/disk-io.c
>> +++ b/disk-io.c
>> @@ -983,14 +983,17 @@ int btrfs_setup_all_roots(struct btrfs_fs_info
>> *fs_info, u64 root_tree_bytenr,
>>       fs_info->last_trans_committed = generation;
>>       if (extent_buffer_uptodate(fs_info->extent_root->node) &&
>>           !(flags & OPEN_CTREE_NO_BLOCK_GROUPS)) {
>> -        ret = btrfs_read_block_groups(fs_info->tree_root);
>> +        ret = btrfs_read_block_groups(fs_info);
>>           /*
>>            * If we don't find any blockgroups (ENOENT) we're either
>>            * restoring or creating the filesystem, where it's expected,
>>            * anything else is error
>>            */
>> -        if (ret != -ENOENT)
>> -            return -EIO;
>> +        if (ret < 0 && ret != -ENOENT) {
>> +            errno = -ret;
>> +            error("failed to read block groups: %m");
>> +            return ret;
>> +        }
>>       }
> 
> 
> As mentioned this alters the rescue command semantics as show below.
> Earlier we had only -EIO as error now its much more and accurate
> which is good. fstests is fine but anything else?
> 
> cmd_rescue_chunk_recover()
>   btrfs_recover_chunk_tree()
>     open_ctree_with_broken_chunk()
>       btrfs_setup_all_roots()

I'm not sure if I got the point.

Although btrfs_setup_all_roots() get called in above call chain, it
doesn't have any special handling of -EIO or others.

It just reads the extent tree root.

Would you mind to explain a little more?

Thanks,
Qu


> 
> Thanks, Anand
> 
>>       key.objectid = BTRFS_FS_TREE_OBJECTID;
>> diff --git a/extent-tree.c b/extent-tree.c
>> index 19d1ea0df570..9713d627764c 100644
>> --- a/extent-tree.c
>> +++ b/extent-tree.c
>> @@ -2607,6 +2607,13 @@ int btrfs_free_block_groups(struct
>> btrfs_fs_info *info)
>>       return 0;
>>   }
>>   +/*
>> + * Find a block group which starts >= @key->objectid in extent tree.
>> + *
>> + * Return 0 for found
>> + * Retrun >0 for not found
>> + * Return <0 for error
>> + */
>>   static int find_first_block_group(struct btrfs_root *root,
>>           struct btrfs_path *path, struct btrfs_key *key)
>>   {
>> @@ -2636,36 +2643,95 @@ static int find_first_block_group(struct
>> btrfs_root *root,
>>               return 0;
>>           path->slots[0]++;
>>       }
>> -    ret = -ENOENT;
>> +    ret = 1;
>>   error:
>>       return ret;
>>   }
>>   -int btrfs_read_block_groups(struct btrfs_root *root)
>> +/*
>> + * Helper function to read out one BLOCK_GROUP_ITEM and insert it into
>> + * block group cache.
>> + *
>> + * Return 0 if nothing wrong (either insert the bg cache or skip 0
>> sized bg)
>> + * Return <0 for error.
>> + */
>> +static int read_one_block_group(struct btrfs_fs_info *fs_info,
>> +                 struct btrfs_path *path)
>>   {
>> -    struct btrfs_path *path;
>> -    int ret;
>> -    int bit;
>> -    struct btrfs_block_group_cache *cache;
>> -    struct btrfs_fs_info *info = root->fs_info;
>> +    struct extent_io_tree *block_group_cache =
>> &fs_info->block_group_cache;
>> +    struct extent_buffer *leaf = path->nodes[0];
>>       struct btrfs_space_info *space_info;
>> -    struct extent_io_tree *block_group_cache;
>> +    struct btrfs_block_group_cache *cache;
>>       struct btrfs_key key;
>> -    struct btrfs_key found_key;
>> -    struct extent_buffer *leaf;
>> +    int slot = path->slots[0];
>> +    int bit = 0;
>> +    int ret;
>>   -    block_group_cache = &info->block_group_cache;
>> +    btrfs_item_key_to_cpu(leaf, &key, slot);
>> +    ASSERT(key.type == BTRFS_BLOCK_GROUP_ITEM_KEY);
>> +
>> +    /*
>> +     * Skip 0 sized block group, don't insert them into block
>> +     * group cache tree, as its length is 0, it won't get
>> +     * freed at close_ctree() time.
>> +     */
>> +    if (key.offset == 0)
>> +        return 0;
>> +
>> +    cache = kzalloc(sizeof(*cache), GFP_NOFS);
>> +    if (!cache)
>> +        return -ENOMEM;
>> +    read_extent_buffer(leaf, &cache->item,
>> +               btrfs_item_ptr_offset(leaf, slot),
>> +               sizeof(cache->item));
>> +    memcpy(&cache->key, &key, sizeof(key));
>> +    cache->cached = 0;
>> +    cache->pinned = 0;
>> +    cache->flags = btrfs_block_group_flags(&cache->item);
>> +    if (cache->flags & BTRFS_BLOCK_GROUP_DATA) {
>> +        bit = BLOCK_GROUP_DATA;
>> +    } else if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
>> +        bit = BLOCK_GROUP_SYSTEM;
>> +    } else if (cache->flags & BTRFS_BLOCK_GROUP_METADATA) {
>> +        bit = BLOCK_GROUP_METADATA;
>> +    }
>> +    set_avail_alloc_bits(fs_info, cache->flags);
>> +    if (btrfs_chunk_readonly(fs_info, cache->key.objectid))
>> +        cache->ro = 1;
>> +    exclude_super_stripes(fs_info, cache);
>> +
>> +    ret = update_space_info(fs_info, cache->flags, cache->key.offset,
>> +                btrfs_block_group_used(&cache->item),
>> +                &space_info);
>> +    if (ret < 0) {
>> +        free(cache);
>> +        return ret;
>> +    }
>> +    cache->space_info = space_info;
>> +
>> +    set_extent_bits(block_group_cache, cache->key.objectid,
>> +            cache->key.objectid + cache->key.offset - 1,
>> +            bit | EXTENT_LOCKED);
>> +    set_state_private(block_group_cache, cache->key.objectid,
>> +              (unsigned long)cache);
>> +    return 0;
>> +}
>>   -    root = info->extent_root;
>> +int btrfs_read_block_groups(struct btrfs_fs_info *fs_info)
>> +{
>> +    struct btrfs_path path;
>> +    struct btrfs_root *root;
>> +    int ret;
>> +    struct btrfs_key key;
>> +
>> +    root = fs_info->extent_root;
>>       key.objectid = 0;
>>       key.offset = 0;
>>       key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
>> -    path = btrfs_alloc_path();
>> -    if (!path)
>> -        return -ENOMEM;
>> +    btrfs_init_path(&path);
>>         while(1) {
>> -        ret = find_first_block_group(root, path, &key);
>> +        ret = find_first_block_group(root, &path, &key);
>>           if (ret > 0) {
>>               ret = 0;
>>               goto error;
>> @@ -2673,67 +2739,21 @@ int btrfs_read_block_groups(struct btrfs_root
>> *root)
>>           if (ret != 0) {
>>               goto error;
>>           }
>> -        leaf = path->nodes[0];
>> -        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
>> +        btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
>>   -        cache = kzalloc(sizeof(*cache), GFP_NOFS);
>> -        if (!cache) {
>> -            ret = -ENOMEM;
>> +        ret = read_one_block_group(fs_info, &path);
>> +        if (ret < 0)
>>               goto error;
>> -        }
>>   -        read_extent_buffer(leaf, &cache->item,
>> -                   btrfs_item_ptr_offset(leaf, path->slots[0]),
>> -                   sizeof(cache->item));
>> -        memcpy(&cache->key, &found_key, sizeof(found_key));
>> -        cache->cached = 0;
>> -        cache->pinned = 0;
>> -        key.objectid = found_key.objectid + found_key.offset;
>> -        if (found_key.offset == 0)
>> +        if (key.offset == 0)
>>               key.objectid++;
>> -        btrfs_release_path(path);
>> -
>> -        /*
>> -         * Skip 0 sized block group, don't insert them into block
>> -         * group cache tree, as its length is 0, it won't get
>> -         * freed at close_ctree() time.
>> -         */
>> -        if (found_key.offset == 0) {
>> -            free(cache);
>> -            continue;
>> -        }
>> -
>> -        cache->flags = btrfs_block_group_flags(&cache->item);
>> -        bit = 0;
>> -        if (cache->flags & BTRFS_BLOCK_GROUP_DATA) {
>> -            bit = BLOCK_GROUP_DATA;
>> -        } else if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
>> -            bit = BLOCK_GROUP_SYSTEM;
>> -        } else if (cache->flags & BTRFS_BLOCK_GROUP_METADATA) {
>> -            bit = BLOCK_GROUP_METADATA;
>> -        }
>> -        set_avail_alloc_bits(info, cache->flags);
>> -        if (btrfs_chunk_readonly(info, cache->key.objectid))
>> -            cache->ro = 1;
>> -
>> -        exclude_super_stripes(info, cache);
>> -
>> -        ret = update_space_info(info, cache->flags, found_key.offset,
>> -                    btrfs_block_group_used(&cache->item),
>> -                    &space_info);
>> -        BUG_ON(ret);
>> -        cache->space_info = space_info;
>> -
>> -        /* use EXTENT_LOCKED to prevent merging */
>> -        set_extent_bits(block_group_cache, found_key.objectid,
>> -                found_key.objectid + found_key.offset - 1,
>> -                bit | EXTENT_LOCKED);
>> -        set_state_private(block_group_cache, found_key.objectid,
>> -                  (unsigned long)cache);
>> +        else
>> +            key.objectid = key.objectid + key.offset;
>> +        btrfs_release_path(&path);
>>       }
>>       ret = 0;
>>   error:
>> -    btrfs_free_path(path);
>> +    btrfs_release_path(&path);
>>       return ret;
>>   }
>>  
> 


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