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libfs: massage path_from_stashed() to allow custom stashing behavior 

* Add a callback to struct stashed_operations so it's possible to
  implement custom behavior for pidfs and allow for it to return errors.

* Teach stashed_dentry_get() to handle error pointers.

Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-2-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-06-18 22:53:36 +02:00
parent 1a1ad73aa1
commit bda3f1608d
2 changed files with 23 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/internal.h
View File

@ -322,12 +322,15 @@ struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);
struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap); struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap);
void mnt_idmap_put(struct mnt_idmap *idmap); void mnt_idmap_put(struct mnt_idmap *idmap);
struct stashed_operations { struct stashed_operations {
struct dentry *(*stash_dentry)(struct dentry **stashed,
struct dentry *dentry);
void (*put_data)(void *data); void (*put_data)(void *data);
int (*init_inode)(struct inode *inode, void *data); int (*init_inode)(struct inode *inode, void *data);
}; };
int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data, int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
struct path *path); struct path *path);
void stashed_dentry_prune(struct dentry *dentry); void stashed_dentry_prune(struct dentry *dentry);
struct dentry *stash_dentry(struct dentry **stashed, struct dentry *dentry);
struct dentry *stashed_dentry_get(struct dentry **stashed); struct dentry *stashed_dentry_get(struct dentry **stashed);
/** /**
* path_mounted - check whether path is mounted * path_mounted - check whether path is mounted

27
fs/libfs.c
View File

@ -2128,6 +2128,8 @@ struct dentry *stashed_dentry_get(struct dentry **stashed)
dentry = rcu_dereference(*stashed); dentry = rcu_dereference(*stashed);
if (!dentry) if (!dentry)
return NULL; return NULL;
if (IS_ERR(dentry))
return dentry;
if (!lockref_get_not_dead(&dentry->d_lockref)) if (!lockref_get_not_dead(&dentry->d_lockref))
return NULL; return NULL;
return dentry; return dentry;
@ -2176,8 +2178,7 @@ static struct dentry *prepare_anon_dentry(struct dentry **stashed,
return dentry; return dentry;
} }
static struct dentry *stash_dentry(struct dentry **stashed, struct dentry *stash_dentry(struct dentry **stashed, struct dentry *dentry)
struct dentry *dentry)
{ {
guard(rcu)(); guard(rcu)();
for (;;) { for (;;) {
@ -2218,12 +2219,15 @@ static struct dentry *stash_dentry(struct dentry **stashed,
int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data, int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
struct path *path) struct path *path)
{ {
struct dentry *dentry; struct dentry *dentry, *res;
const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info; const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info;
/* See if dentry can be reused. */ /* See if dentry can be reused. */
path->dentry = stashed_dentry_get(stashed); res = stashed_dentry_get(stashed);
if (path->dentry) { if (IS_ERR(res))
return PTR_ERR(res);
if (res) {
path->dentry = res;
sops->put_data(data); sops->put_data(data);
goto out_path; goto out_path;
} }
@ -2234,8 +2238,17 @@ int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
return PTR_ERR(dentry); return PTR_ERR(dentry);
/* Added a new dentry. @data is now owned by the filesystem. */ /* Added a new dentry. @data is now owned by the filesystem. */
path->dentry = stash_dentry(stashed, dentry); if (sops->stash_dentry)
if (path->dentry != dentry) res = sops->stash_dentry(stashed, dentry);
else
res = stash_dentry(stashed, dentry);
if (IS_ERR(res)) {
dput(dentry);
return PTR_ERR(res);
}
path->dentry = res;
/* A dentry was reused. */
if (res != dentry)
dput(dentry); dput(dentry);
out_path: out_path: