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kernfs: add a revision to identify directory node changes

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Add a revision counter to kernfs directory nodes so it can be used
to detect if a directory node has changed during negative dentry
revalidation.

There's an assumption that sizeof(unsigned long) <= sizeof(pointer)
on all architectures and as far as I know that assumption holds.

So adding a revision counter to the struct kernfs_elem_dir variant of
the kernfs_node type union won't increase the size of the kernfs_node
struct. This is because struct kernfs_elem_dir is at least
sizeof(pointer) smaller than the largest union variant. It's tempting
to make the revision counter a u64 but that would increase the size of
kernfs_node on archs where sizeof(pointer) is smaller than the revision
counter.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/162642769895.63632.8356662784964509867.stgit@web.messagingengine.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Kent 2021-07-16 17:28:18 +08:00 committed by Greg Kroah-Hartman
parent bdac4d8abb
commit 895adbec30
3 changed files with 26 additions and 0 deletions
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2
fs/kernfs/dir.c
View File

@ -372,6 +372,7 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
/* successfully added, account subdir number */
if (kernfs_type(kn) == KERNFS_DIR)
kn->parent->dir.subdirs++;
kernfs_inc_rev(kn->parent);
return 0;
}
@ -394,6 +395,7 @@ static bool kernfs_unlink_sibling(struct kernfs_node *kn)
if (kernfs_type(kn) == KERNFS_DIR)
kn->parent->dir.subdirs--;
kernfs_inc_rev(kn->parent);
rb_erase(&kn->rb, &kn->parent->dir.children);
RB_CLEAR_NODE(&kn->rb);

19
fs/kernfs/kernfs-internal.h
View File

@ -81,6 +81,25 @@ static inline struct kernfs_node *kernfs_dentry_node(struct dentry *dentry)
return d_inode(dentry)->i_private;
}
static inline void kernfs_set_rev(struct kernfs_node *parent,
struct dentry *dentry)
{
dentry->d_time = parent->dir.rev;
}
static inline void kernfs_inc_rev(struct kernfs_node *parent)
{
parent->dir.rev++;
}
static inline bool kernfs_dir_changed(struct kernfs_node *parent,
struct dentry *dentry)
{
if (parent->dir.rev != dentry->d_time)
return true;
return false;
}
extern const struct super_operations kernfs_sops;
extern struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;

5
include/linux/kernfs.h
View File

@ -98,6 +98,11 @@ struct kernfs_elem_dir {
* better directly in kernfs_node but is here to save space.
*/
struct kernfs_root *root;
/*
* Monotonic revision counter, used to identify if a directory
* node has changed during negative dentry revalidation.
*/
unsigned long rev;
};
struct kernfs_elem_symlink {