[PATCH V2 01/12] kernfs: implement i_generation

[Shaohua Li]

From: Shaohua Li <s...@fb.com>

Set i_generation for kernfs inode. This is required to implement exportfs
operations.

Note, the generation is 32-bit, so it's possible the generation wraps up
and we find stale files. The possiblity is low, since fhandle matches
both inode number and generation. In most fs, the generation is 32-bit.
fhandle only export 32-bit generation for most fs. So unless we have
solid reason, we'd live with the possible conflict.

Signed-off-by: Shaohua Li <s...@fb.com>
---
 fs/kernfs/dir.c        | 2 ++
 fs/kernfs/inode.c      | 1 +
 include/linux/kernfs.h | 2 ++
 3 files changed, 5 insertions(+)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index db5900aaa..09d093e 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -634,6 +634,7 @@ static struct kernfs_node *__kernfs_new_node(struct 
kernfs_root *root,
        if (ret < 0)
                goto err_out2;
        kn->ino = ret;
+       kn->generation = atomic_inc_return(&root->next_generation);
 
        atomic_set(&kn->count, 1);
        atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
@@ -877,6 +878,7 @@ struct kernfs_root *kernfs_create_root(struct 
kernfs_syscall_ops *scops,
 
        ida_init(&root->ino_ida);
        INIT_LIST_HEAD(&root->supers);
+       atomic_set(&root->next_generation, 0);
 
        kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
                               KERNFS_DIR);
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index fb4b4a7..79cdae4 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -220,6 +220,7 @@ static void kernfs_init_inode(struct kernfs_node *kn, 
struct inode *inode)
        inode->i_private = kn;
        inode->i_mapping->a_ops = &kernfs_aops;
        inode->i_op = &kernfs_iops;
+       inode->i_generation = kn->generation;
 
        set_default_inode_attr(inode, kn->mode);
        kernfs_refresh_inode(kn, inode);
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index a9b11b8..c5f0fa7 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -135,6 +135,7 @@ struct kernfs_node {
        umode_t                 mode;
        unsigned int            ino;
        struct kernfs_iattrs    *iattr;
+       u32                     generation;
 };
 
 /*
@@ -170,6 +171,7 @@ struct kernfs_root {
        struct list_head        supers;
 
        wait_queue_head_t       deactivate_waitq;
+       atomic_t                next_generation;
 };
 
 struct kernfs_open_file {
-- 
2.9.3