[PATCH v5 09/22] liveupdate: luo_session: Add ioctls for file preservation and state management

Pasha Tatashin
2025-11-07T21:05:50Z

Introducing the userspace interface and internal logic required to
manage the lifecycle of file descriptors within a session. Previously, a
session was merely a container; this change makes it a functional
management unit.

The following capabilities are added:

A new set of ioctl commands are added, which operate on the file
descriptor returned by CREATE_SESSION. This allows userspace to:
- LIVEUPDATE_SESSION_PRESERVE_FD: Add a file descriptor to a session
to be preserved across the live update.
- LIVEUPDATE_SESSION_UNPRESERVE_FD: Remove a previously added file
descriptor from the session.
- LIVEUPDATE_SESSION_RESTORE_FD: Retrieve a preserved file in the
new kernel using its unique token.

A state machine for each individual session, distinct from the global
LUO state. This enables more granular control, allowing userspace to
prepare or freeze specific sessions independently. This is managed via:
- LIVEUPDATE_SESSION_SET_EVENT: An ioctl to send PREPARE, FREEZE,
CANCEL, or FINISH events to a single session.
- LIVEUPDATE_SESSION_GET_STATE: An ioctl to query the current state
of a single session.

The global subsystem callbacks (luo_session_prepare, luo_session_freeze)
are updated to iterate through all existing sessions. They now trigger
the appropriate per-session state transitions for any sessions that
haven't already been transitioned individually by userspace.

The session's .release handler is enhanced to be state-aware. When a
session's file descriptor is closed, it now correctly cancels or
finishes the session based on its current state before freeing all
associated file resources, preventing resource leaks.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/uapi/linux/liveupdate.h | 104 ++++++++++++++++++
kernel/liveupdate/luo_session.c | 183 +++++++++++++++++++++++++++++++-
2 files changed, 283 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index 3ce60e976ecc..c55b3c7a1a39 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -53,6 +53,14 @@ enum {
LIVEUPDATE_CMD_RETRIEVE_SESSION = 0x01,
};

+/* ioctl commands for session file descriptors */
+enum {
+ LIVEUPDATE_CMD_SESSION_BASE = 0x40,
+ LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE,
+ LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41,
+ LIVEUPDATE_CMD_SESSION_FINISH = 0x42,
+};
+
/**
* struct liveupdate_ioctl_create_session - ioctl(LIVEUPDATE_IOCTL_CREATE_SESSION)
* @size: Input; sizeof(struct liveupdate_ioctl_create_session)
@@ -110,4 +118,100 @@ struct liveupdate_ioctl_retrieve_session {
#define LIVEUPDATE_IOCTL_RETRIEVE_SESSION \
_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_RETRIEVE_SESSION)

+/* Session specific IOCTLs */
+
+/**
+ * struct liveupdate_session_preserve_fd - ioctl(LIVEUPDATE_SESSION_PRESERVE_FD)
+ * @size: Input; sizeof(struct liveupdate_session_preserve_fd)
+ * @fd: Input; The user-space file descriptor to be preserved.
+ * @token: Input; An opaque, unique token for preserved resource.
+ *
+ * Holds parameters for preserving Validate and initiate preservation for a file
+ * descriptor.
+ *
+ * User sets the @fd field identifying the file descriptor to preserve
+ * (e.g., memfd, kvm, iommufd, VFIO). The kernel validates if this FD type
+ * and its dependencies are supported for preservation. If validation passes,
+ * the kernel marks the FD internally and *initiates the process* of preparing
+ * its state for saving. The actual snapshotting of the state typically occurs
+ * during the subsequent %LIVEUPDATE_IOCTL_PREPARE execution phase, though
+ * some finalization might occur during freeze.
+ * On successful validation and initiation, the kernel uses the @token
+ * field with an opaque identifier representing the resource being preserved.
+ * This token confirms the FD is targeted for preservation and is required for
+ * the subsequent %LIVEUPDATE_SESSION_RETRIEVE_FD call after the live update.
+ *
+ * Return: 0 on success (validation passed, preservation initiated), negative
+ * error code on failure (e.g., unsupported FD type, dependency issue,
+ * validation failed).
+ */
+struct liveupdate_session_preserve_fd {
+ __u32 size;
+ __s32 fd;
+ __aligned_u64 token;
+};
+
+#define LIVEUPDATE_SESSION_PRESERVE_FD \
+ _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_PRESERVE_FD)
+
+/**
+ * struct liveupdate_session_retrieve_fd - ioctl(LIVEUPDATE_SESSION_RETRIEVE_FD)
+ * @size: Input; sizeof(struct liveupdate_session_RETRIEVE_fd)
+ * @fd: Output; The new file descriptor representing the fully restored
+ * kernel resource.
+ * @token: Input; An opaque, token that was used to preserve the resource.
+ *
+ * Retrieve a previously preserved file descriptor.
+ *
+ * User sets the @token field to the value obtained from a successful
+ * %LIVEUPDATE_IOCTL_FD_PRESERVE call before the live update. On success,
+ * the kernel restores the state (saved during the PREPARE/FREEZE phases)
+ * associated with the token and populates the @fd field with a new file
+ * descriptor referencing the restored resource in the current (new) kernel.
+ * This operation must be performed *before* signaling completion via
+ * %LIVEUPDATE_IOCTL_FINISH.
+ *
+ * Return: 0 on success, negative error code on failure (e.g., invalid token).
+ */
+struct liveupdate_session_retrieve_fd {
+ __u32 size;
+ __s32 fd;
+ __aligned_u64 token;
+};
+
+#define LIVEUPDATE_SESSION_RETRIEVE_FD \
+ _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_RETRIEVE_FD)
+
+/**
+ * struct liveupdate_session_finish - ioctl(LIVEUPDATE_SESSION_FINISH)
+ * @size: Input; sizeof(struct liveupdate_session_finish)
+ * @reserved: Input; Must be zero. Reserved for future use.
+ *
+ * Signals the completion of the restoration process for a retrieved session.
+ * This is the final operation that should be performed on a session file
+ * descriptor after a live update.
+ *
+ * This ioctl must be called once all required file descriptors for the session
+ * have been successfully retrieved (using %LIVEUPDATE_SESSION_RETRIEVE_FD) and
+ * are fully restored from the userspace and kernel perspective.
+ *
+ * Upon success, the kernel releases its ownership of the preserved resources
+ * associated with this session. This allows internal resources to be freed,
+ * typically by decrementing reference counts on the underlying preserved
+ * objects.
+ *
+ * If this operation fails, the resources remain preserved in memory. Userspace
+ * may attempt to call finish again. The resources will otherwise be reset
+ * during the next live update cycle.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+struct liveupdate_session_finish {
+ __u32 size;
+ __u8 reserved[2];
+};
+
+#define LIVEUPDATE_SESSION_FINISH \
+ _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH)
+
#endif /* _UAPI_LIVEUPDATE_H */
diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index a3513118aa74..ec526de83987 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -164,26 +164,185 @@ static void luo_session_remove(struct luo_session_head *sh,
sh->count--;
}

+static int luo_session_finish_one(struct luo_session *session)
+{
+ guard(mutex)(&session->mutex);
+ return luo_file_finish(session);
+}
+
+static void luo_session_unfreeze_one(struct luo_session *session)
+{
+ guard(mutex)(&session->mutex);
+ luo_file_unfreeze(session);
+}
+
+static int luo_session_freeze_one(struct luo_session *session)
+{
+ guard(mutex)(&session->mutex);
+ return luo_file_freeze(session);
+}
+
static int luo_session_release(struct inode *inodep, struct file *filep)
{
struct luo_session *session = filep->private_data;
struct luo_session_head *sh;
+ int err = 0;

/* If retrieved is set, it means this session is from incoming list */
- if (session->retrieved)
+ if (session->retrieved) {
sh = &luo_session_global.incoming;
- else
+
+ err = luo_session_finish_one(session);
+ if (err) {
+ pr_warn("Unable to finish session [%s] on release\n",
+ session->name);
+ } else {
+ luo_session_remove(sh, session);
+ luo_session_free(session);
+ }
+
+ } else {
sh = &luo_session_global.outgoing;

- luo_session_remove(sh, session);
- luo_session_free(session);
+ scoped_guard(mutex, &session->mutex)
+ luo_file_unpreserve_files(session);
+ luo_session_remove(sh, session);
+ luo_session_free(session);
+ }
+
+ return err;
+}
+
+static int luo_session_preserve_fd(struct luo_session *session,
+ struct luo_ucmd *ucmd)
+{
+ struct liveupdate_session_preserve_fd *argp = ucmd->cmd;
+ int err;
+
+ guard(mutex)(&session->mutex);
+ err = luo_preserve_file(session, argp->token, argp->fd);
+ if (err)
+ return err;
+
+ err = luo_ucmd_respond(ucmd, sizeof(*argp));
+ if (err)
+ pr_warn("The file was successfully preserved, but response to user failed\n");
+
+ return err;
+}
+
+static int luo_session_retrieve_fd(struct luo_session *session,
+ struct luo_ucmd *ucmd)
+{
+ struct liveupdate_session_retrieve_fd *argp = ucmd->cmd;
+ struct file *file;
+ int err;
+
+ argp->fd = get_unused_fd_flags(O_CLOEXEC);
+ if (argp->fd < 0)
+ return argp->fd;
+
+ guard(mutex)(&session->mutex);
+ err = luo_retrieve_file(session, argp->token, &file);
+ if (err < 0) {
+ put_unused_fd(argp->fd);
+
+ return err;
+ }
+
+ err = luo_ucmd_respond(ucmd, sizeof(*argp));
+ if (err)
+ return err;
+
+ fd_install(argp->fd, file);

return 0;
}

+static int luo_session_finish(struct luo_session *session,
+ struct luo_ucmd *ucmd)
+{
+ struct liveupdate_session_finish *argp = ucmd->cmd;
+ int err = luo_session_finish_one(session);
+
+ if (err)
+ return err;
+
+ return luo_ucmd_respond(ucmd, sizeof(*argp));
+}
+
+union ucmd_buffer {
+ struct liveupdate_session_finish finish;
+ struct liveupdate_session_preserve_fd preserve;
+ struct liveupdate_session_retrieve_fd retrieve;
+};
+
+struct luo_ioctl_op {
+ unsigned int size;
+ unsigned int min_size;
+ unsigned int ioctl_num;
+ int (*execute)(struct luo_session *session, struct luo_ucmd *ucmd);
+};
+
+#define IOCTL_OP(_ioctl, _fn, _struct, _last) \
+ [_IOC_NR(_ioctl) - LIVEUPDATE_CMD_SESSION_BASE] = { \
+ .size = sizeof(_struct) + \
+ BUILD_BUG_ON_ZERO(sizeof(union ucmd_buffer) < \
+ sizeof(_struct)), \
+ .min_size = offsetofend(_struct, _last), \
+ .ioctl_num = _ioctl, \
+ .execute = _fn, \
+ }
+
+static const struct luo_ioctl_op luo_session_ioctl_ops[] = {
+ IOCTL_OP(LIVEUPDATE_SESSION_FINISH, luo_session_finish,
+ struct liveupdate_session_finish, reserved),
+ IOCTL_OP(LIVEUPDATE_SESSION_PRESERVE_FD, luo_session_preserve_fd,
+ struct liveupdate_session_preserve_fd, token),
+ IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd,
+ struct liveupdate_session_retrieve_fd, token),
+};
+
+static long luo_session_ioctl(struct file *filep, unsigned int cmd,
+ unsigned long arg)
+{
+ struct luo_session *session = filep->private_data;
+ const struct luo_ioctl_op *op;
+ struct luo_ucmd ucmd = {};
+ union ucmd_buffer buf;
+ unsigned int nr;
+ int ret;
+
+ nr = _IOC_NR(cmd);
+ if (nr < LIVEUPDATE_CMD_SESSION_BASE || (nr - LIVEUPDATE_CMD_SESSION_BASE) >=
+ ARRAY_SIZE(luo_session_ioctl_ops)) {
+ return -EINVAL;
+ }
+
+ ucmd.ubuffer = (void __user *)arg;
+ ret = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer);
+ if (ret)
+ return ret;
+
+ op = &luo_session_ioctl_ops[nr - LIVEUPDATE_CMD_SESSION_BASE];
+ if (op->ioctl_num != cmd)
+ return -ENOIOCTLCMD;
+ if (ucmd.user_size < op->min_size)
+ return -EINVAL;
+
+ ucmd.cmd = &buf;
+ ret = copy_struct_from_user(ucmd.cmd, op->size, ucmd.ubuffer,
+ ucmd.user_size);
+ if (ret)
+ return ret;
+
+ return op->execute(session, &ucmd);
+}
+
static const struct file_operations luo_session_fops = {
.owner = THIS_MODULE,
.release = luo_session_release,
+ .unlocked_ioctl = luo_session_ioctl,
};

/* Create a "struct file" for session */
@@ -375,6 +534,8 @@ int luo_session_deserialize(void)
session->count = sh->ser[i].count;
session->files = __va(sh->ser[i].files);
session->pgcnt = sh->ser[i].pgcnt;
+ scoped_guard(mutex, &session->mutex)
+ luo_file_deserialize(session);
}

luo_free_restore(sh->head_ser, sh->head_ser->pgcnt << PAGE_SHIFT);
@@ -389,9 +550,14 @@ int luo_session_serialize(void)
struct luo_session_head *sh = &luo_session_global.outgoing;
struct luo_session *session;
int i = 0;
+ int err;

guard(rwsem_write)(&sh->rwsem);
list_for_each_entry(session, &sh->list, list) {
+ err = luo_session_freeze_one(session);
+ if (err)
+ goto err_undo;
+
strscpy(sh->ser[i].name, session->name,
sizeof(sh->ser[i].name));
sh->ser[i].count = session->count;
@@ -402,4 +568,13 @@ int luo_session_serialize(void)
sh->head_ser->count = sh->count;

return 0;
+
+err_undo:
+ list_for_each_entry_continue_reverse(session, &sh->list, list) {
+ luo_session_unfreeze_one(session);
+ memset(&sh->ser[i], 0, sizeof(sh->ser[i]));
+ i--;
+ }
+
+ return err;
}
--
2.51.2.1041.gc1ab5b90ca-goog