On Tue, Oct 17, 2017 at 7:44 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> To allow reconnecting of pure upper overlay dentry based on its
> real parent, we restrict the implementation to encoding of overlay
> dentries with pure upper ancestry up to overlay root.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/export.c | 70 ++++++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 61 insertions(+), 9 deletions(-)
>
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index 33914f23530e..263415dd929b 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -17,15 +17,40 @@
> #include "overlayfs.h"
> #include "ovl_entry.h"
>
> +/* Check if dentry is pure upper ancestry up to root */
> +static bool ovl_is_pure_upper_or_root(struct dentry *dentry, int connectable)
> +{
> + struct dentry *parent = NULL;
> +
> + /* For non-connectable non-dir we don't need to check ancestry */
> + if (!d_is_dir(dentry) && !connectable)
> + return !ovl_dentry_lower(dentry);
> +
> + dget(dentry);
> + while (!IS_ROOT(dentry) && !ovl_dentry_lower(dentry)) {
> + parent = dget_parent(dentry);
> + dput(dentry);
> + dentry = parent;
> + }
> + dput(dentry);
> +
> + return dentry == dentry->d_sb->s_root;
> +}
> +
> /* TODO: add export_operations method dentry_to_fh() ??? */
> static int ovl_dentry_to_fh(struct dentry *dentry, struct fid *fid,
> int *max_len, int connectable)
> {
> - struct dentry *lower = ovl_dentry_lower(dentry);
> int type;
>
> - /* TODO: handle encoding of non pure upper */
> - if (lower)
> + /*
> + * Overlay root dir inode is hashed and encoded as pure upper, because
> + * root dir dentry is born upper and not indexed. It is not a problem
> + * that root dir is not indexed, because root dentry is pinned to cache.
> + *
> + * TODO: handle encoding of non pure upper.
> + */
> + if (!ovl_is_pure_upper_or_root(dentry, connectable))
> return FILEID_INVALID;
>
> /*
> @@ -40,20 +65,47 @@ static int ovl_dentry_to_fh(struct dentry *dentry, struct fid *fid,
> return type;
> }
>
> +/* Find an alias of inode. If @dir is non NULL, find a child alias */
> +static struct dentry *ovl_find_alias(struct inode *inode, struct inode *dir)
> +{
> + struct dentry *parent, *child;
> + struct dentry *alias = NULL;
> +
> + /* Parent inode is never provided when encoding a directory */
> + if (!dir || WARN_ON(!S_ISDIR(dir->i_mode) || S_ISDIR(inode->i_mode)))
> + return d_find_alias(inode);
> +
> + /*
> + * Run all of the dentries associated with this parent. Since this is
> + * a directory, there damn well better only be one item on this list.
> + */
FYI, this iteration is breaking locking order.
I pushed a fix patch to iterate on aliases looking for match with parent
to branch ovl-nfs-export-v1.
This code was not exercised by my xfstests because name_to_handle_at()
does not encode connectable file handles.
I use a test patch (at the tip of ovl-nfs-export-v1) to encode connectable
file handles from name_to_handle_at() to test this code.
> + spin_lock(&dir->i_lock);
> + hlist_for_each_entry(parent, &dir->i_dentry, d_u.d_alias) {
> + /* Find an alias of inode who is a child of parent */
> + spin_lock(&parent->d_lock);
> + list_for_each_entry(child, &parent->d_subdirs, d_child) {
> + if (child->d_inode == inode) {
> + alias = dget(child);
> + break;
> + }
> + }
> + spin_unlock(&parent->d_lock);
> + }
> + spin_unlock(&dir->i_lock);
> +
> + return alias;
> +}
> +
> static int ovl_encode_inode_fh(struct inode *inode, u32 *fh, int *max_len,
> struct inode *parent)
> {
> - struct dentry *dentry = d_find_alias(inode);
> + struct dentry *dentry = ovl_find_alias(inode, parent);
> int type;
>
> if (!dentry)
> return FILEID_INVALID;
>
> - /* TODO: handle encoding of non-dir connectable file handle */
> - if (parent)
> - return FILEID_INVALID;
> -
> - type = ovl_dentry_to_fh(dentry, (struct fid *)fh, max_len, 0);
> + type = ovl_dentry_to_fh(dentry, (struct fid *)fh, max_len, !!parent);
>
> dput(dentry);
> return type;
> --
> 2.7.4
>
