Re: [PATCH 1/7] fs: btrfs: Introduce btrfs_for_each_slot

Marcos Paulo de Souza
2021-08-25T13:33:50Z

On Wed, 2021-08-25 at 07:42 +0000, Johannes Thumshirn wrote:
> On 24/08/2021 19:13, Marcos Paulo de Souza wrote:
> > There is a common pattern when search for a key in btrfs:
> >
> > * Call btrfs_search_slot
> > * Endless loop
> > * If the found slot is bigger than the current items in the
> > leaf, check the
> > next one
> > * If still not found in the next leaf, return 1
> > * Do something with the code
> > * Increment current slot, and continue
> >
> > This pattern can be improved by creating an iterator macro, similar
> > to
> > those for_each_X already existing in the linux kernel. Using this
> > approach means to reduce significantly boilerplate code, along
> > making it
> > easier to newcomers to understand how to code works.
> >
> > Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> > ---
> > fs/btrfs/ctree.c | 28 ++++++++++++++++++++++++++++
> > fs/btrfs/ctree.h | 25 +++++++++++++++++++++++++
> > fs/btrfs/xattr.c | 40 ++++++++++++----------------------------
> > 3 files changed, 65 insertions(+), 28 deletions(-)
> >
> > diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> > index 84627cbd5b5b..b1aa6e3987d0 100644
> > --- a/fs/btrfs/ctree.c
> > +++ b/fs/btrfs/ctree.c
> > @@ -2122,6 +2122,34 @@ int btrfs_search_backwards(struct btrfs_root
> > *root, struct btrfs_key *key,
> > return ret;
> > }
> >
> > +/* Search for a valid slot for the given path.
> > + * @root: The root node of the tree.
> > + * @key: Will contain a valid item if found.
> > + * @path: The start point to validate the slot.
> > + *
> > + * Return 0 if the item is valid, 1 if not found and < 0 if error.
> > + */
> > +int btrfs_valid_slot(struct btrfs_root *root, struct btrfs_key
> > *key,
> > + struct btrfs_path *path)
> > +{
> > + while (1) {
> > + int ret;
> > + const int slot = path->slots[0];
> > + const struct extent_buffer *leaf = path->nodes[0];
> > +
> > + if (slot >= btrfs_header_nritems(leaf)) {
> > + ret = btrfs_next_leaf(root, path);
> > + if (ret)
> > + return ret;
> > + continue;
> > + }
> > + btrfs_item_key_to_cpu(leaf, key, slot);
> > + break;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > /*
> > * adjust the pointers going up the tree, starting at level
> > * making sure the right key of each node is points to 'key'.
> > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > index f07c82fafa04..1e3c4a7741ca 100644
> > --- a/fs/btrfs/ctree.h
> > +++ b/fs/btrfs/ctree.h
> > @@ -2912,6 +2912,31 @@ int btrfs_next_old_leaf(struct btrfs_root
> > *root, struct btrfs_path *path,
> > int btrfs_search_backwards(struct btrfs_root *root, struct
> > btrfs_key *key,
> > struct btrfs_path *path);
> >
> > +int btrfs_valid_slot(struct btrfs_root *root, struct btrfs_key
> > *key,
> > + struct btrfs_path *path);
> > +
> > +/* Search in @root for a given @key, and store the slot found in
> > @found_key.
> > + * @root: The root node of the tree.
> > + * @key: The key we are looking for.
> > + * @found_key: Will hold the found item.
> > + * @path: Holds the current slot/leaf.
> > + * @iter_ret: Contains the returned value from btrfs_search_slot
> > and
> > + * btrfs_valid_slot, whatever is executed later.
> > + *
> > + * The iter_ret is an output variable that will contain the result
> > of the
> > + * btrfs_search_slot if it returns an error, or the value returned
> > from
> > + * btrfs_valid_slot otherwise. The return value can be 0 if the
> > something was
> > + * found, 1 if there weren't bigger leaves, and <0 if error.
> > + */
> > +#define btrfs_for_each_slot(root, key, found_key, path, iter_ret)
> > \
> > + for (iter_ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
> > \
> > + (
> > \
> > + iter_ret >= 0 &&
> > \
> > + (iter_ret = btrfs_valid_slot(root, found_key,
> > path)) == 0 \
> > + );
> > \
> > + path->slots[0]++
> > \
> > + )
> > +
> > static inline int btrfs_next_old_item(struct btrfs_root *root,
> > struct btrfs_path *p, u64
> > time_seq)
> > {
>
> Shouldn't below xattr code be in a separate patch? Just like the
> block-group,
> dev-replace, etc changes?

You're right, this was a leftover of my RFC patches. I'll send a new
version as soon.

>
> > diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> > index 8a4514283a4b..f85febba1891 100644
> > --- a/fs/btrfs/xattr.c
> > +++ b/fs/btrfs/xattr.c
> > @@ -274,10 +274,12 @@ int btrfs_setxattr_trans(struct inode *inode,
> > const char *name,
> > ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer,
> > size_t size)
> > {
> > struct btrfs_key key;
> > + struct btrfs_key found_key;
> > struct inode *inode = d_inode(dentry);
> > struct btrfs_root *root = BTRFS_I(inode)->root;
> > struct btrfs_path *path;
> > int ret = 0;
> > + int iter_ret = 0;
> > size_t total_size = 0, size_left = size;
> >
> > /*
> > @@ -295,44 +297,22 @@ ssize_t btrfs_listxattr(struct dentry
> > *dentry, char *buffer, size_t size)
> > path->reada = READA_FORWARD;
> >
> > /* search for our xattrs */
> > - ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> > - if (ret < 0)
> > - goto err;
> > -
> > - while (1) {
> > + btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
> > struct extent_buffer *leaf;
> > int slot;
> > struct btrfs_dir_item *di;
> > - struct btrfs_key found_key;
> > u32 item_size;
> > u32 cur;
> >
> > leaf = path->nodes[0];
> > slot = path->slots[0];
> >
> > - /* this is where we start walking through the path */
> > - if (slot >= btrfs_header_nritems(leaf)) {
> > - /*
> > - * if we've reached the last slot in this leaf
> > we need
> > - * to go to the next leaf and reset everything
> > - */
> > - ret = btrfs_next_leaf(root, path);
> > - if (ret < 0)
> > - goto err;
> > - else if (ret > 0)
> > - break;
> > - continue;
> > - }
> > -
> > - btrfs_item_key_to_cpu(leaf, &found_key, slot);
> > -
> > /* check to make sure this item is what we want */
> > - if (found_key.objectid != key.objectid)
> > - break;
> > - if (found_key.type > BTRFS_XATTR_ITEM_KEY)
> > + if (found_key.objectid != key.objectid ||
> > + found_key.type > BTRFS_XATTR_ITEM_KEY)
> > break;
> > if (found_key.type < BTRFS_XATTR_ITEM_KEY)
> > - goto next_item;
> > + continue;
> >
> > di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
> > item_size = btrfs_item_size_nr(leaf, slot);
> > @@ -365,9 +345,13 @@ ssize_t btrfs_listxattr(struct dentry *dentry,
> > char *buffer, size_t size)
> > cur += this_len;
> > di = (struct btrfs_dir_item *)((char *)di +
> > this_len);
> > }
> > -next_item:
> > - path->slots[0]++;
> > }
> > +
> > + if (iter_ret < 0) {
> > + ret = iter_ret;
> > + goto err;
> > + }
> > +
> > ret = total_size;
> >
> > err:
> >