On Tue 13-02-24 16:37:39, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> For simple filesystems that use directory offset mapping, rely
> strictly on the directory offset map to tell when a directory has
> no children.
>
> After this patch is applied, the emptiness test holds only the RCU
> read lock when the directory being tested has no children.
>
> In addition, this adds another layer of confirmation that
> simple_offset_add/remove() are working as expected.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Makes sense. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/libfs.c | 32 ++++++++++++++++++++++++++++++++
> include/linux/fs.h | 1 +
> mm/shmem.c | 4 ++--
> 3 files changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index a38af72f4719..3cf773950f93 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -313,6 +313,38 @@ void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
> offset_set(dentry, 0);
> }
>
> +/**
> + * simple_offset_empty - Check if a dentry can be unlinked
> + * @dentry: dentry to be tested
> + *
> + * Returns 0 if @dentry is a non-empty directory; otherwise returns 1.
> + */
> +int simple_offset_empty(struct dentry *dentry)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct offset_ctx *octx;
> + struct dentry *child;
> + unsigned long index;
> + int ret = 1;
> +
> + if (!inode || !S_ISDIR(inode->i_mode))
> + return ret;
> +
> + index = 2;
> + octx = inode->i_op->get_offset_ctx(inode);
> + xa_for_each(&octx->xa, index, child) {
> + spin_lock(&child->d_lock);
> + if (simple_positive(child)) {
> + spin_unlock(&child->d_lock);
> + ret = 0;
> + break;
> + }
> + spin_unlock(&child->d_lock);
> + }
> +
> + return ret;
> +}
> +
> /**
> * simple_offset_rename_exchange - exchange rename with directory offsets
> * @old_dir: parent of dentry being moved
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ed5966a70495..03d141809a2c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3267,6 +3267,7 @@ struct offset_ctx {
> void simple_offset_init(struct offset_ctx *octx);
> int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry);
> void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry);
> +int simple_offset_empty(struct dentry *dentry);
> int simple_offset_rename_exchange(struct inode *old_dir,
> struct dentry *old_dentry,
> struct inode *new_dir,
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d7c84ff62186..6fed524343cb 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3374,7 +3374,7 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
>
> static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
> {
> - if (!simple_empty(dentry))
> + if (!simple_offset_empty(dentry))
> return -ENOTEMPTY;
>
> drop_nlink(d_inode(dentry));
> @@ -3431,7 +3431,7 @@ static int shmem_rename2(struct mnt_idmap *idmap,
> return simple_offset_rename_exchange(old_dir, old_dentry,
> new_dir, new_dentry);
>
> - if (!simple_empty(new_dentry))
> + if (!simple_offset_empty(new_dentry))
> return -ENOTEMPTY;
>
> if (flags & RENAME_WHITEOUT) {
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
