[PATCH 0/1] liveupdate: Add internal APIs for file preservation

[PATCH 0/1] liveupdate: Add internal APIs for file preservation

[Samiullah Khawaja]

Live update orchestrator file handlers depend on the preservation of
other files. To make sure that the dependency is preserved, the file
handlers needs to fetch the preservation token of the preserved
dependency. Similarly during restore, a file handler wants to fetch the
restored file of the dependency.

There are two known usecases of this,

- VFIO-Cdev preservation requires the preservation of iommufd. This is
  required by the IOMMU preservation series:
  https://lore.kernel.org/all/20260427175633.1978233-1-skhawaja@google.com/
- guest_memfd preservation requires the preservation of kvmfd. This is
  required by the guest_memfd preservation series:
  https://lore.kernel.org/all/20ae20f9d1a198b289444ebb4c824314cbba1bcf.1780676742.git.tarunsahu@google.com/

This patch was being sent as part of the IOMMU preservation series, but
now it is being sent separately.

Pasha Tatashin (1):
  liveupdate: luo_file: Add internal APIs for file preservation

 include/linux/liveupdate.h       | 21 ++++++++++
 kernel/liveupdate/luo_file.c     | 69 ++++++++++++++++++++++++++++++++
 kernel/liveupdate/luo_internal.h | 17 ++++++++
 3 files changed, 107 insertions(+)

base-commit: 34e8f02817e31826e76bb2ded48bf28fe921f20b
-- 
2.54.0.1136.gdb2ca164c4-goog

[PATCH 1/1] liveupdate: luo_file: Add internal APIs for file preservation

[Samiullah Khawaja]

From: Pasha Tatashin <pasha.tatashin@soleen.com>

Live update orchestrator file handlers depend on the preservation of
other files. To make sure that the dependency is preserved, the file
handlers needs to fetch the preservation token of the preserved
dependency. Similarly during restore, a file handler wants to fetch the
restored file of the dependency.

Add APIs that allows fetching token of dependency during preservation,
and fetching the restored file dependency during restore.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
---
 include/linux/liveupdate.h       | 21 ++++++++++
 kernel/liveupdate/luo_file.c     | 69 ++++++++++++++++++++++++++++++++
 kernel/liveupdate/luo_internal.h | 17 ++++++++
 3 files changed, 107 insertions(+)

diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 88722e5caf02..261f61998fce 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -25,6 +25,7 @@ struct file;
 /**
  * struct liveupdate_file_op_args - Arguments for file operation callbacks.
  * @handler:          The file handler being called.
+ * @session:          The session this file belongs to.
  * @retrieve_status:  The retrieve status for the 'can_finish / finish'
  *                    operation. A value of 0 means the retrieve has not been
  *                    attempted, a positive value means the retrieve was
@@ -45,6 +46,7 @@ struct file;
  */
 struct liveupdate_file_op_args {
 	struct liveupdate_file_handler *handler;
+	struct liveupdate_session *session;
 	int retrieve_status;
 	struct file *file;
 	u64 serialized_data;
@@ -243,6 +245,13 @@ int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp);
 void liveupdate_flb_put_incoming(struct liveupdate_flb *flb);
 
 int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp);
+/* kernel can internally retrieve files */
+int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
+				 struct file **filep);
+
+/* Get a token for an outgoing file, or -ENOENT if file is not preserved */
+int liveupdate_get_token_outgoing(struct liveupdate_session *s,
+				  struct file *file, u64 *tokenp);
 
 #else /* CONFIG_LIVEUPDATE */
 
@@ -292,5 +301,17 @@ static inline int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb,
 	return -EOPNOTSUPP;
 }
 
+static inline int liveupdate_get_file_incoming(struct liveupdate_session *s,
+					       u64 token, struct file **filep)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int liveupdate_get_token_outgoing(struct liveupdate_session *s,
+						struct file *file, u64 *tokenp)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif /* CONFIG_LIVEUPDATE */
 #endif /* _LINUX_LIVEUPDATE_H */
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index f428f720b53f..57f7f19fcfca 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -323,6 +323,7 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	mutex_init(&luo_file->mutex);
 
 	args.handler = fh;
+	args.session = luo_session_from_file_set(file_set);
 	args.file = file;
 	err = fh->ops->preserve(&args);
 	if (err)
@@ -380,6 +381,7 @@ void luo_file_unpreserve_files(struct luo_file_set *file_set)
 					   struct luo_file, list);
 
 		args.handler = luo_file->fh;
+		args.session = luo_session_from_file_set(file_set);
 		args.file = luo_file->file;
 		args.serialized_data = luo_file->serialized_data;
 		args.private_data = luo_file->private_data;
@@ -411,6 +413,7 @@ static int luo_file_freeze_one(struct luo_file_set *file_set,
 		struct liveupdate_file_op_args args = {0};
 
 		args.handler = luo_file->fh;
+		args.session = luo_session_from_file_set(file_set);
 		args.file = luo_file->file;
 		args.serialized_data = luo_file->serialized_data;
 		args.private_data = luo_file->private_data;
@@ -432,6 +435,7 @@ static void luo_file_unfreeze_one(struct luo_file_set *file_set,
 		struct liveupdate_file_op_args args = {0};
 
 		args.handler = luo_file->fh;
+		args.session = luo_session_from_file_set(file_set);
 		args.file = luo_file->file;
 		args.serialized_data = luo_file->serialized_data;
 		args.private_data = luo_file->private_data;
@@ -621,6 +625,7 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
 	}
 
 	args.handler = luo_file->fh;
+	args.session = luo_session_from_file_set(file_set);
 	args.serialized_data = luo_file->serialized_data;
 	err = luo_file->fh->ops->retrieve(&args);
 	if (err) {
@@ -654,6 +659,7 @@ static int luo_file_can_finish_one(struct luo_file_set *file_set,
 		struct liveupdate_file_op_args args = {0};
 
 		args.handler = luo_file->fh;
+		args.session = luo_session_from_file_set(file_set);
 		args.file = luo_file->file;
 		args.serialized_data = luo_file->serialized_data;
 		args.retrieve_status = luo_file->retrieve_status;
@@ -671,6 +677,7 @@ static void luo_file_finish_one(struct luo_file_set *file_set,
 	guard(mutex)(&luo_file->mutex);
 
 	args.handler = luo_file->fh;
+	args.session = luo_session_from_file_set(file_set);
 	args.file = luo_file->file;
 	args.serialized_data = luo_file->serialized_data;
 	args.retrieve_status = luo_file->retrieve_status;
@@ -926,3 +933,65 @@ void liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh)
 	list_del(&ACCESS_PRIVATE(fh, list));
 }
 EXPORT_SYMBOL_GPL(liveupdate_unregister_file_handler);
+
+/**
+ * liveupdate_get_token_outgoing - Get the token for a preserved file.
+ * @s:      The outgoing liveupdate session.
+ * @file:   The file object to search for.
+ * @tokenp: Output parameter for the found token.
+ *
+ * Searches the list of preserved files in an outgoing session for a matching
+ * file object. If found, the corresponding user-provided token is returned.
+ *
+ * This function is intended for in-kernel callers that need to correlate a
+ * file with its liveupdate token.
+ *
+ * Context: It must be called with session mutex acquired.
+ * Return: 0 on success, -ENOENT if the file is not preserved in this session.
+ */
+int liveupdate_get_token_outgoing(struct liveupdate_session *s,
+				  struct file *file, u64 *tokenp)
+{
+	struct luo_file_set *file_set = luo_file_set_from_session_locked(s);
+	struct luo_file *luo_file;
+	int err = -ENOENT;
+
+	list_for_each_entry(luo_file, &file_set->files_list, list) {
+		if (luo_file->file == file) {
+			if (tokenp)
+				*tokenp = luo_file->token;
+			err = 0;
+			break;
+		}
+	}
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(liveupdate_get_token_outgoing);
+
+/**
+ * liveupdate_get_file_incoming - Retrieves a preserved file for in-kernel use.
+ * @s:      The incoming liveupdate session (restored from the previous kernel).
+ * @token:  The unique token identifying the file to retrieve.
+ * @filep:  On success, this will be populated with a pointer to the retrieved
+ *          'struct file'.
+ *
+ * Provides a kernel-internal API for other subsystems to retrieve their
+ * preserved files after a live update. This function is a simple wrapper
+ * around luo_retrieve_file(), allowing callers to find a file by its token.
+ *
+ * The caller receives a new reference to the file and must call fput() when it
+ * is no longer needed. The file's lifetime is managed by LUO and any userspace
+ * file descriptors.
+ *
+ * Context: It must be called with session mutex acquired of a restored session.
+ * Return: 0 on success. Returns -ENOENT if no file with the matching token is
+ *         found, or any other negative errno on failure.
+ */
+int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
+				 struct file **filep)
+{
+	return luo_retrieve_file(luo_file_set_from_session_locked(s),
+				 token, filep);
+}
+EXPORT_SYMBOL_GPL(liveupdate_get_file_incoming);
diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
index 875844d7a41d..08b198802e7f 100644
--- a/kernel/liveupdate/luo_internal.h
+++ b/kernel/liveupdate/luo_internal.h
@@ -79,6 +79,23 @@ struct luo_session {
 
 extern struct rw_semaphore luo_register_rwlock;
 
+static inline struct liveupdate_session *luo_session_from_file_set(struct luo_file_set *file_set)
+{
+	struct luo_session *session;
+
+	session = container_of(file_set, struct luo_session, file_set);
+
+	return (struct liveupdate_session *)session;
+}
+
+static inline struct luo_file_set *luo_file_set_from_session_locked(struct liveupdate_session *s)
+{
+	struct luo_session *session = (struct luo_session *)s;
+
+	lockdep_assert_held(&session->mutex);
+	return &session->file_set;
+}
+
 int luo_session_create(const char *name, struct file **filep);
 int luo_session_retrieve(const char *name, struct file **filep);
 int __init luo_session_setup_outgoing(void *fdt);
-- 
2.54.0.1136.gdb2ca164c4-goog

Re: [PATCH 1/1] liveupdate: luo_file: Add internal APIs for file preservation

[Pranjal Shrivastava]

On Sat, Jun 13, 2026 at 01:25:20AM +0000, Samiullah Khawaja wrote:
> From: Pasha Tatashin <pasha.tatashin@soleen.com>
> 
> Live update orchestrator file handlers depend on the preservation of
> other files. To make sure that the dependency is preserved, the file
> handlers needs to fetch the preservation token of the preserved
> dependency. Similarly during restore, a file handler wants to fetch the
> restored file of the dependency.
> 
> Add APIs that allows fetching token of dependency during preservation,
> and fetching the restored file dependency during restore.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  include/linux/liveupdate.h       | 21 ++++++++++
>  kernel/liveupdate/luo_file.c     | 69 ++++++++++++++++++++++++++++++++
>  kernel/liveupdate/luo_internal.h | 17 ++++++++
>  3 files changed, 107 insertions(+)
>
[...]
> +EXPORT_SYMBOL_GPL(liveupdate_get_token_outgoing);
> +
> +/**
> + * liveupdate_get_file_incoming - Retrieves a preserved file for in-kernel use.
> + * @s:      The incoming liveupdate session (restored from the previous kernel).
> + * @token:  The unique token identifying the file to retrieve.
> + * @filep:  On success, this will be populated with a pointer to the retrieved
> + *          'struct file'.
> + *
> + * Provides a kernel-internal API for other subsystems to retrieve their
> + * preserved files after a live update. This function is a simple wrapper
> + * around luo_retrieve_file(), allowing callers to find a file by its token.
> + *
> + * The caller receives a new reference to the file and must call fput() when it
> + * is no longer needed. The file's lifetime is managed by LUO and any userspace
> + * file descriptors.
> + *
> + * Context: It must be called with session mutex acquired of a restored session.
> + * Return: 0 on success. Returns -ENOENT if no file with the matching token is
> + *         found, or any other negative errno on failure.
> + */
> +int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> +				 struct file **filep)
> +{
> +	return luo_retrieve_file(luo_file_set_from_session_locked(s),
> +				 token, filep);
> +}
> +EXPORT_SYMBOL_GPL(liveupdate_get_file_incoming);

Thanks for modifying the comment (as discussed in [1]). 
This looks good now, along with the EXPORT_SYMBOL_GPL.

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan

[1] https://lore.kernel.org/all/agr6yoyYYq2QFxjL@google.com/