[PATCH 08/10] kernfs: implement custom exportfs ops and fid type

Tejun Heo
2019-11-05T00:00:30Z

The current kernfs exportfs implementation uses the generic_fh_*()
helpers and FILEID_INO32_GEN[_PARENT] which limits ino to 32bits.
Let's implement custom exportfs operations and fid type to remove the
restriction.

* FILEID_KERNFS is a single u64 value whose content is
kernfs_node->id. This is the only native fid type.

* For backward compatibility with blk_log_action() path which exposes
(ino,gen) pairs which userland assembles into FILEID_INO32_GEN keys,
combine the generic keys into 64bit IDs in the same order.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
---
fs/kernfs/mount.c | 77 +++++++++++++++++++++++++++++++---------
include/linux/exportfs.h | 5 +++
2 files changed, 66 insertions(+), 16 deletions(-)

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 8aed2cccd002..37a1e5df117a 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -53,40 +53,84 @@ const struct super_operations kernfs_sops = {
.show_path = kernfs_sop_show_path,
};

-static struct inode *kernfs_fh_get_inode(struct super_block *sb,
- u64 ino, u32 generation)
+static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
+ struct inode *parent)
+{
+ struct kernfs_node *kn = inode->i_private;
+
+ if (*max_len < 2) {
+ *max_len = 2;
+ return FILEID_INVALID;
+ }
+
+ *max_len = 2;
+ *(u64 *)fh = kn->id;
+ return FILEID_KERNFS;
+}
+
+static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
+ struct fid *fid, int fh_len,
+ int fh_type, bool get_parent)
{
struct kernfs_super_info *info = kernfs_info(sb);
- struct inode *inode;
struct kernfs_node *kn;
+ struct inode *inode;
+ u64 id;

- if (ino == 0)
- return ERR_PTR(-ESTALE);
+ if (fh_len < 2)
+ return NULL;
+
+ switch (fh_type) {
+ case FILEID_KERNFS:
+ id = *(u64 *)fid;
+ break;
+ case FILEID_INO32_GEN:
+ case FILEID_INO32_GEN_PARENT:
+ /*
+ * blk_log_action() exposes (ino,gen) pair without type and
+ * userland can call us with generic fid constructed from
+ * them. Combine it back to ID. See blk_log_action().
+ */
+ id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
+ break;
+ default:
+ return NULL;
+ }

- kn = kernfs_find_and_get_node_by_id(info->root,
- ino | ((u64)generation << 32));
+ kn = kernfs_find_and_get_node_by_id(info->root, id);
if (!kn)
return ERR_PTR(-ESTALE);
+
+ if (get_parent) {
+ struct kernfs_node *parent;
+
+ parent = kernfs_get_parent(kn);
+ kernfs_put(kn);
+ kn = parent;
+ if (!kn)
+ return ERR_PTR(-ESTALE);
+ }
+
inode = kernfs_get_inode(sb, kn);
kernfs_put(kn);
if (!inode)
return ERR_PTR(-ESTALE);

- return inode;
+ return d_obtain_alias(inode);
}

-static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
- int fh_len, int fh_type)
+static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
+ struct fid *fid, int fh_len,
+ int fh_type)
{
- return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
- kernfs_fh_get_inode);
+ return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
}

-static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
- int fh_len, int fh_type)
+static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
+ struct fid *fid, int fh_len,
+ int fh_type)
{
- return generic_fh_to_parent(sb, fid, fh_len, fh_type,
- kernfs_fh_get_inode);
+ return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
}

static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
@@ -97,6 +141,7 @@ static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
}

static const struct export_operations kernfs_export_ops = {
+ .encode_fh = kernfs_encode_fh,
.fh_to_dentry = kernfs_fh_to_dentry,
.fh_to_parent = kernfs_fh_to_parent,
.get_parent = kernfs_get_parent_dentry,
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index cf6571fc9c01..d896b8657085 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -104,6 +104,11 @@ enum fid_type {
*/
FILEID_LUSTRE = 0x97,

+ /*
+ * 64 bit unique kernfs id
+ */
+ FILEID_KERNFS = 0xfe,
+
/*
* Filesystems must not use 0xff file ID.
*/
--
2.17.1