On 22.11.2017 00:20, Edmund Nadolski wrote:
>
>
> On 11/21/2017 12:59 AM, Nikolay Borisov wrote:
>>
>>
>> On 20.11.2017 22:24, Edmund Nadolski wrote:
>>> Improve code documentation by adding/expanding comments in
>>> several places.
>>>
>>> Signed-off-by: Edmund Nadolski <enadol...@suse.com>
>>> ---
>>> fs/btrfs/ctree.c | 31 +++++++++++++++-------
>>> fs/btrfs/ctree.h | 28 +++++++++++++++-----
>>> fs/btrfs/extent_map.h | 58
>>> ++++++++++++++++++++++++++++-------------
>>> fs/btrfs/file-item.c | 3 +++
>>> fs/btrfs/inode.c | 21 +++++++++++----
>>> include/uapi/linux/btrfs_tree.h | 1 +
>>> 6 files changed, 104 insertions(+), 38 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>>> index 531e0a8..9331d02 100644
>>> --- a/fs/btrfs/ctree.c
>>> +++ b/fs/btrfs/ctree.c
>>> @@ -2654,17 +2654,30 @@ int btrfs_find_item(struct btrfs_root *fs_root,
>>> struct btrfs_path *path,
>>> }
>>>
>>> /*
>>> - * look for key in the tree. path is filled in with nodes along the way
>>> - * if key is found, we return zero and you can find the item in the leaf
>>> - * level of the path (level 0)
>>> + * Search a btree for a specific key. Optionally update the btree for
>>> + * item insertion or removal.
>>> *
>>> - * If the key isn't found, the path points to the slot where it should
>>> - * be inserted, and 1 is returned. If there are other errors during the
>>> - * search a negative error number is returned.
>>> + * @trans - Transaction handle (NULL for none, requires @cow == 0).
>>> + * @root - The btree to be searched.
>>> + * @key - key for search.
>>> + * @p - Points to a btrfs_path to be populated with btree node and index
>>> + * values encountered during traversal. (See also struct btrfs_path.)
>>> + * @ins_len - byte length of item as follows:
>>> + * >0: byte length of item for insertion. Btree nodes/leaves are
>>> + * split as required.
>>> + * <0: byte length of item for deletion. Btree nodes/leaves are
>>> + * merged as required.
>>> + * 0: Do not modify the btree (search only).
>>> + * @cow - 0 to nocow, or !0 to cow for btree update.
>>> *
>>> - * if ins_len > 0, nodes and leaves will be split as we walk down the
>>> - * tree. if ins_len < 0, nodes will be merged as we walk down the tree (if
>>> - * possible)
>>> + * Return values:
>>> + * 0: @key was found and @p was updated to indicate the leaf and item
>>> + * slot where the item may be accessed.
>>> + * 1: @key was not found and @p was updated to indicate the leaf and
>>> + * item slot where the item may be inserted.
>>> + * <0: an error occurred.
>>> + *
>>> + * Note, insertion/removal updates will re-balance the btree as needed.
>>> */
>>> int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
>>> *root,
>>> const struct btrfs_key *key, struct btrfs_path *p,
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 2154b5a..e980caa 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -318,20 +318,36 @@ struct btrfs_node {
>>> } __attribute__ ((__packed__));
>>>
>>> /*
>>> - * btrfs_paths remember the path taken from the root down to the leaf.
>>> - * level 0 is always the leaf, and nodes[1...BTRFS_MAX_LEVEL] will point
>>> - * to any other levels that are present.
>>> - *
>>> - * The slots array records the index of the item or block pointer
>>> - * used while walking the tree.
>>> + * Used with btrfs_search_slot() to record a btree search path traversed
>>> from a
>>> + * root down to a leaf.
>>> */
>>> enum { READA_NONE = 0, READA_BACK, READA_FORWARD };
>>> struct btrfs_path {
>>> + /*
>>> + * The nodes[] and slots[] arrays are indexed according to btree
>>> + * levels. Index 0 corresponds to the lowest (leaf) level. Increasing
>>> + * indexes correspond to interior btree nodes at subsequently higher
>>> + * levels.
>>> + *
>>> + * nodes[0] always points to a leaf. nodes[1] points to a btree node
>>> + * which contains a block pointer referencing that leaf. For higher
>>> + * indexes, node[n] points to a btree node which contains a block
>>> + * pointer referencing node[n-1].
>>> + */
>>> struct extent_buffer *nodes[BTRFS_MAX_LEVEL];
>>> +
>>> + /*
>>> + * The slots[0] value identifies an item index in the leaf at nodes[0].
>>> + * Each slots[n] value identifies a block pointer index in the
>>> + * corresponding tree node at nodes[n].
>>> + */
>>> int slots[BTRFS_MAX_LEVEL];
>>> +
>>> /* if there is real range locking, this locks field will change */
>>> u8 locks[BTRFS_MAX_LEVEL];
>>> +
>>> u8 reada;
>>> +
>>> /* keep some upper locks as we walk down */
>>> u8 lowest_level;
>>>
>>> diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
>>> index 64365bb..34ea85c3 100644
>>> --- a/fs/btrfs/extent_map.h
>>> +++ b/fs/btrfs/extent_map.h
>>> @@ -5,35 +5,57 @@
>>> #include <linux/rbtree.h>
>>> #include <linux/refcount.h>
>>>
>>> -#define EXTENT_MAP_LAST_BYTE ((u64)-4)
>>> -#define EXTENT_MAP_HOLE ((u64)-3)
>>> -#define EXTENT_MAP_INLINE ((u64)-2)
>>> -#define EXTENT_MAP_DELALLOC ((u64)-1)
>>> -
>>> -/* bits for the flags field */
>>> -#define EXTENT_FLAG_PINNED 0 /* this entry not yet on disk, don't free it
>>> */
>>> -#define EXTENT_FLAG_COMPRESSED 1
>>> -#define EXTENT_FLAG_VACANCY 2 /* no file extent item found */
>>> -#define EXTENT_FLAG_PREALLOC 3 /* pre-allocated extent */
>>> -#define EXTENT_FLAG_LOGGING 4 /* Logging this extent */
>>> -#define EXTENT_FLAG_FILLING 5 /* Filling in a preallocated extent */
>>> -#define EXTENT_FLAG_FS_MAPPING 6 /* filesystem extent mapping type */
>>> +/*
>>> + * Reserve some special-case values for the extent_map .start,
>>> .block_start,
>>> + *: and .orig_start fields.
>> ^ extra :
>
> Thanks, will fix.
>
>
>>> + */
>>> +#define EXTENT_MAP_LAST_BYTE ((u64)-4) /* Lowest reserved
>>> value */
>>> +#define EXTENT_MAP_HOLE ((u64)-3) /* Unwritten extent */
>>> +#define EXTENT_MAP_INLINE ((u64)-2) /* Inlined file data */
>>> +#define EXTENT_MAP_DELALLOC ((u64)-1) /* Delayed block
>>> allocation */
>>
>> These values are only set/checked on the .block_start parameter so you
>> can possibly remove the .start/.orig_start from the above comment.
>
> Seems there still are a few tucked away:
>
> $ grep -n " = EXTENT_MAP_" *.[ch] | grep -v block_start
> file-item.c:996: em->orig_start = EXTENT_MAP_HOLE;
> inode.c:6969: em->start = EXTENT_MAP_HOLE;
> inode.c:6970: em->orig_start = EXTENT_MAP_HOLE;
As a matter of fact I think those are redundant/buggy since they are
never checked. So I gues you can fold their removal in this patch.
>
> Thanks,
> Ed
>
>
>>>
>>> +/*
>>> + * Bit flags for the extent_map .flags field.
>>> + */
>>> +#define EXTENT_FLAG_PINNED 0 /* entry not yet on disk, don't free it */
>>> +#define EXTENT_FLAG_COMPRESSED 1
>>> +#define EXTENT_FLAG_VACANCY 2 /* no file extent item found */
>>> +#define EXTENT_FLAG_PREALLOC 3 /* pre-allocated extent */
>>> +#define EXTENT_FLAG_LOGGING 4 /* Logging this extent */
>>> +#define EXTENT_FLAG_FILLING 5 /* Filling in a preallocated extent */
>>> +#define EXTENT_FLAG_FS_MAPPING 6 /* filesystem extent mapping type */
>>> +
>>> +/*
>>> + * In-memory representation of a file extent (regular/prealloc/inline).
>>> + */
>>
>> <rant>
>> I just realise how badly named this struct is. Because we really have
>> on-disk extents and in-memory extents (similar to XFS nomenclature) and
>> the extent_map name doesn't really bring those 2 things together
>> </rant>
>>
>>> struct extent_map {
>>> struct rb_node rb_node;
>>>
>>> /* all of these are in bytes */
>>> - u64 start;
>>> - u64 len;
>>> + u64 start; /* logical byte offset in the file */
>>> + u64 len; /* byte length of extent in the file */
>>> u64 mod_start;
>>> u64 mod_len;
>>> u64 orig_start;
>>> u64 orig_block_len;
>>> +
>>> + /* max. bytes needed to hold the (uncompressed) extent in memory. */
>>> u64 ram_bytes;
>>> +
>>> + /*
>>> + * For regular/prealloc, block_start is a logical address denoting the
>>> + * start of the extent data, and block_len is the on-disk byte length
>>> + * of the extent (which may be comressed). block_start may be
>>> + * EXTENT_MAP_HOLE if the extent is unwritten. For inline, block_start
>>> + * is EXTENT_MAP_INLINE and block_len is (u64)-1. See also
>>> + * btrfs_extent_item_to_extent_map() and btrfs_get_extent().
>>> + */
>>> u64 block_start;
>>> u64 block_len;
>>> - u64 generation;
>>> - unsigned long flags;
>>> +
>>> + u64 generation; /* transaction id */
>>> + unsigned long flags; /* EXTENT_FLAG_* bit flags as above */
>>> +
>>> union {
>>> struct block_device *bdev;
>>>
>>> @@ -44,7 +66,7 @@ struct extent_map {
>>> struct map_lookup *map_lookup;
>>> };
>>> refcount_t refs;
>>> - unsigned int compress_type;
>>> + unsigned int compress_type; /* BTRFS_COMPRESS_* */
>>> struct list_head list;
>>> };
>>>
>>> diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
>>> index fdcb410..5d63172 100644
>>> --- a/fs/btrfs/file-item.c
>>> +++ b/fs/btrfs/file-item.c
>>> @@ -929,6 +929,9 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle
>>> *trans,
>>> goto out;
>>> }
>>>
>>> +/*
>>> + * Populate an extent_map from the btrfs_file_extent_item contents.
>>> + */
>>> void btrfs_extent_item_to_extent_map(struct btrfs_inode *inode,
>>> const struct btrfs_path *path,
>>> struct btrfs_file_extent_item *fi,
>>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>>> index 72c7b38..b6d5d94 100644
>>> --- a/fs/btrfs/inode.c
>>> +++ b/fs/btrfs/inode.c
>>> @@ -6916,17 +6916,28 @@ static noinline int uncompress_inline(struct
>>> btrfs_path *path,
>>> }
>>>
>>> /*
>>> - * a bit scary, this does extent mapping from logical file offset to the
>>> disk.
>>> - * the ugly parts come from merging extents from the disk with the in-ram
>>> + * btrfs_get_extent - find or create an extent_map for the (@start, @len)
>>> range.
>>> + *
>>> + * @inode - inode containing the desired extent.
>>> + * @page - page for inlined extent (NULL if none)
>>> + * @page_offset - byte offset within @page
>>> + * @start - logical byte offset in the file.
>>> + * @len - byte length of the range.
>>> + * @create - for inlined extents: 0 to update @page with extent data from
>>> + * the item; 1 to bypass the update.
>>> + *
>>> + * A bit scary, this does extent mapping from logical file offset to the
>>> disk.
>>> + * The ugly parts come from merging extents from the disk with the in-ram
>>> * representation. This gets more complex because of the data=ordered
>>> code,
>>> * where the in-ram extents might be locked pending data=ordered
>>> completion.
>>> *
>>> * This also copies inline extents directly into the page.
>>> + *
>>> + * Returns the extent_map, or error code.
>>> */> struct extent_map *btrfs_get_extent(struct btrfs_inode *inode,
>>> - struct page *page,
>>> - size_t pg_offset, u64 start, u64 len,
>>> - int create)
>>> + struct page *page, size_t pg_offset,
>>> + u64 start, u64 len, int create)
>>> {
>>> struct btrfs_fs_info *fs_info = btrfs_sb(inode->vfs_inode.i_sb);
>>> int ret;
>>> diff --git a/include/uapi/linux/btrfs_tree.h
>>> b/include/uapi/linux/btrfs_tree.h
>>> index 6d6e5da..693636a 100644
>>> --- a/include/uapi/linux/btrfs_tree.h
>>> +++ b/include/uapi/linux/btrfs_tree.h
>>> @@ -730,6 +730,7 @@ struct btrfs_balance_item {
>>> __le64 unused[4];
>>> } __attribute__ ((__packed__));
>>>
>>> +/* Values for .type field in btrfs_file_extent_item */
>>> #define BTRFS_FILE_EXTENT_INLINE 0
>>> #define BTRFS_FILE_EXTENT_REG 1
>>> #define BTRFS_FILE_EXTENT_PREALLOC 2
>>>
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