From: Pasha Tatashin Date: Tue, 25 Nov 2025 16:58:35 +0000 (-0500) Subject: liveupdate: luo_core: add user interface X-Git-Tag: v6.19-rc1~70^2~26 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=81cd25d263a182b3dcdc8af3b92e4b8e4db336de;p=thirdparty%2Fkernel%2Flinux.git liveupdate: luo_core: add user interface Introduce the user-space interface for the Live Update Orchestrator via ioctl commands, enabling external control over the live update process and management of preserved resources. The idea is that there is going to be a single userspace agent driving the live update, therefore, only a single process can ever hold this device opened at a time. The following ioctl commands are introduced: LIVEUPDATE_IOCTL_CREATE_SESSION Provides a way for userspace to create a named session for grouping file descriptors that need to be preserved. It returns a new file descriptor representing the session. LIVEUPDATE_IOCTL_RETRIEVE_SESSION Allows the userspace agent in the new kernel to reclaim a preserved session by its name, receiving a new file descriptor to manage the restored resources. Link: https://lkml.kernel.org/r/20251125165850.3389713-6-pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin Reviewed-by: Mike Rapoport (Microsoft) Reviewed-by: Pratyush Yadav Tested-by: David Matlack Cc: Aleksander Lobakin Cc: Alexander Graf Cc: Alice Ryhl Cc: Andriy Shevchenko Cc: anish kumar Cc: Anna Schumaker Cc: Bartosz Golaszewski Cc: Bjorn Helgaas Cc: Borislav Betkov Cc: Chanwoo Choi Cc: Chen Ridong Cc: Chris Li Cc: Christian Brauner Cc: Daniel Wagner Cc: Danilo Krummrich Cc: Dan Williams Cc: David Hildenbrand Cc: David Jeffery Cc: David Rientjes Cc: Greg Kroah-Hartman Cc: Guixin Liu Cc: "H. Peter Anvin" Cc: Hugh Dickins Cc: Ilpo Järvinen Cc: Ingo Molnar Cc: Ira Weiny Cc: Jann Horn Cc: Jason Gunthorpe Cc: Jens Axboe Cc: Joanthan Cameron Cc: Joel Granados Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Lennart Poettering Cc: Leon Romanovsky Cc: Leon Romanovsky Cc: Lukas Wunner Cc: Marc Rutland Cc: Masahiro Yamada Cc: Matthew Maurer Cc: Miguel Ojeda Cc: Myugnjoo Ham Cc: Parav Pandit Cc: Pratyush Yadav Cc: Randy Dunlap Cc: Roman Gushchin Cc: Saeed Mahameed Cc: Samiullah Khawaja Cc: Song Liu Cc: Steven Rostedt Cc: Stuart Hayes Cc: Tejun Heo Cc: Thomas Gleinxer Cc: Thomas Weißschuh Cc: Vincent Guittot Cc: William Tu Cc: Yoann Congal Cc: Zhu Yanjun Cc: Zijun Hu Signed-off-by: Andrew Morton --- diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h index 40578ae196680..1183cf984b5f8 100644 --- a/include/uapi/linux/liveupdate.h +++ b/include/uapi/linux/liveupdate.h @@ -46,4 +46,68 @@ /* The maximum length of session name including null termination */ #define LIVEUPDATE_SESSION_NAME_LENGTH 64 +/* The /dev/liveupdate ioctl commands */ +enum { + LIVEUPDATE_CMD_BASE = 0x00, + LIVEUPDATE_CMD_CREATE_SESSION = LIVEUPDATE_CMD_BASE, + LIVEUPDATE_CMD_RETRIEVE_SESSION = 0x01, +}; + +/** + * struct liveupdate_ioctl_create_session - ioctl(LIVEUPDATE_IOCTL_CREATE_SESSION) + * @size: Input; sizeof(struct liveupdate_ioctl_create_session) + * @fd: Output; The new file descriptor for the created session. + * @name: Input; A null-terminated string for the session name, max + * length %LIVEUPDATE_SESSION_NAME_LENGTH including termination + * character. + * + * Creates a new live update session for managing preserved resources. + * This ioctl can only be called on the main /dev/liveupdate device. + * + * Return: 0 on success, negative error code on failure. + */ +struct liveupdate_ioctl_create_session { + __u32 size; + __s32 fd; + __u8 name[LIVEUPDATE_SESSION_NAME_LENGTH]; +}; + +#define LIVEUPDATE_IOCTL_CREATE_SESSION \ + _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_CREATE_SESSION) + +/** + * struct liveupdate_ioctl_retrieve_session - ioctl(LIVEUPDATE_IOCTL_RETRIEVE_SESSION) + * @size: Input; sizeof(struct liveupdate_ioctl_retrieve_session) + * @fd: Output; The new file descriptor for the retrieved session. + * @name: Input; A null-terminated string identifying the session to retrieve. + * The name must exactly match the name used when the session was + * created in the previous kernel. + * + * Retrieves a handle (a new file descriptor) for a preserved session by its + * name. This is the primary mechanism for a userspace agent to regain control + * of its preserved resources after a live update. + * + * The userspace application provides the null-terminated `name` of a session + * it created before the live update. If a preserved session with a matching + * name is found, the kernel instantiates it and returns a new file descriptor + * in the `fd` field. This new session FD can then be used for all file-specific + * operations, such as restoring individual file descriptors with + * LIVEUPDATE_SESSION_RETRIEVE_FD. + * + * It is the responsibility of the userspace application to know the names of + * the sessions it needs to retrieve. If no session with the given name is + * found, the ioctl will fail with -ENOENT. + * + * This ioctl can only be called on the main /dev/liveupdate device when the + * system is in the LIVEUPDATE_STATE_UPDATED state. + */ +struct liveupdate_ioctl_retrieve_session { + __u32 size; + __s32 fd; + __u8 name[LIVEUPDATE_SESSION_NAME_LENGTH]; +}; + +#define LIVEUPDATE_IOCTL_RETRIEVE_SESSION \ + _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_RETRIEVE_SESSION) + #endif /* _UAPI_LIVEUPDATE_H */ diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c index a0f7788cd003c..f7ecaf7740d19 100644 --- a/kernel/liveupdate/luo_core.c +++ b/kernel/liveupdate/luo_core.c @@ -41,7 +41,13 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +#include +#include +#include +#include +#include #include +#include #include #include #include @@ -246,12 +252,183 @@ bool liveupdate_enabled(void) return luo_global.enabled; } +/** + * DOC: LUO ioctl Interface + * + * The IOCTL user-space control interface for the LUO subsystem. + * It registers a character device, typically found at ``/dev/liveupdate``, + * which allows a userspace agent to manage the LUO state machine and its + * associated resources, such as preservable file descriptors. + * + * To ensure that the state machine is controlled by a single entity, access + * to this device is exclusive: only one process is permitted to have + * ``/dev/liveupdate`` open at any given time. Subsequent open attempts will + * fail with -EBUSY until the first process closes its file descriptor. + * This singleton model simplifies state management by preventing conflicting + * commands from multiple userspace agents. + */ + struct luo_device_state { struct miscdevice miscdev; + atomic_t in_use; }; +static int luo_ioctl_create_session(struct luo_ucmd *ucmd) +{ + struct liveupdate_ioctl_create_session *argp = ucmd->cmd; + struct file *file; + int err; + + argp->fd = get_unused_fd_flags(O_CLOEXEC); + if (argp->fd < 0) + return argp->fd; + + err = luo_session_create(argp->name, &file); + if (err) + goto err_put_fd; + + err = luo_ucmd_respond(ucmd, sizeof(*argp)); + if (err) + goto err_put_file; + + fd_install(argp->fd, file); + + return 0; + +err_put_file: + fput(file); +err_put_fd: + put_unused_fd(argp->fd); + + return err; +} + +static int luo_ioctl_retrieve_session(struct luo_ucmd *ucmd) +{ + struct liveupdate_ioctl_retrieve_session *argp = ucmd->cmd; + struct file *file; + int err; + + argp->fd = get_unused_fd_flags(O_CLOEXEC); + if (argp->fd < 0) + return argp->fd; + + err = luo_session_retrieve(argp->name, &file); + if (err < 0) + goto err_put_fd; + + err = luo_ucmd_respond(ucmd, sizeof(*argp)); + if (err) + goto err_put_file; + + fd_install(argp->fd, file); + + return 0; + +err_put_file: + fput(file); +err_put_fd: + put_unused_fd(argp->fd); + + return err; +} + +static int luo_open(struct inode *inodep, struct file *filep) +{ + struct luo_device_state *ldev = container_of(filep->private_data, + struct luo_device_state, + miscdev); + + if (atomic_cmpxchg(&ldev->in_use, 0, 1)) + return -EBUSY; + + /* Always return -EIO to user if deserialization fail */ + if (luo_session_deserialize()) { + atomic_set(&ldev->in_use, 0); + return -EIO; + } + + return 0; +} + +static int luo_release(struct inode *inodep, struct file *filep) +{ + struct luo_device_state *ldev = container_of(filep->private_data, + struct luo_device_state, + miscdev); + atomic_set(&ldev->in_use, 0); + + return 0; +} + +union ucmd_buffer { + struct liveupdate_ioctl_create_session create; + struct liveupdate_ioctl_retrieve_session retrieve; +}; + +struct luo_ioctl_op { + unsigned int size; + unsigned int min_size; + unsigned int ioctl_num; + int (*execute)(struct luo_ucmd *ucmd); +}; + +#define IOCTL_OP(_ioctl, _fn, _struct, _last) \ + [_IOC_NR(_ioctl) - LIVEUPDATE_CMD_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_ioctl_ops[] = { + IOCTL_OP(LIVEUPDATE_IOCTL_CREATE_SESSION, luo_ioctl_create_session, + struct liveupdate_ioctl_create_session, name), + IOCTL_OP(LIVEUPDATE_IOCTL_RETRIEVE_SESSION, luo_ioctl_retrieve_session, + struct liveupdate_ioctl_retrieve_session, name), +}; + +static long luo_ioctl(struct file *filep, unsigned int cmd, unsigned long arg) +{ + const struct luo_ioctl_op *op; + struct luo_ucmd ucmd = {}; + union ucmd_buffer buf; + unsigned int nr; + int err; + + nr = _IOC_NR(cmd); + if (nr < LIVEUPDATE_CMD_BASE || + (nr - LIVEUPDATE_CMD_BASE) >= ARRAY_SIZE(luo_ioctl_ops)) { + return -EINVAL; + } + + ucmd.ubuffer = (void __user *)arg; + err = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer); + if (err) + return err; + + op = &luo_ioctl_ops[nr - LIVEUPDATE_CMD_BASE]; + if (op->ioctl_num != cmd) + return -ENOIOCTLCMD; + if (ucmd.user_size < op->min_size) + return -EINVAL; + + ucmd.cmd = &buf; + err = copy_struct_from_user(ucmd.cmd, op->size, ucmd.ubuffer, + ucmd.user_size); + if (err) + return err; + + return op->execute(&ucmd); +} + static const struct file_operations luo_fops = { .owner = THIS_MODULE, + .open = luo_open, + .release = luo_release, + .unlocked_ioctl = luo_ioctl, }; static struct luo_device_state luo_dev = { @@ -260,6 +437,7 @@ static struct luo_device_state luo_dev = { .name = "liveupdate", .fops = &luo_fops, }, + .in_use = ATOMIC_INIT(0), }; static int __init liveupdate_ioctl_init(void) diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h index 05ae91695ec62..1292ac47eef80 100644 --- a/kernel/liveupdate/luo_internal.h +++ b/kernel/liveupdate/luo_internal.h @@ -9,6 +9,27 @@ #define _LINUX_LUO_INTERNAL_H #include +#include + +struct luo_ucmd { + void __user *ubuffer; + u32 user_size; + void *cmd; +}; + +static inline int luo_ucmd_respond(struct luo_ucmd *ucmd, + size_t kernel_cmd_size) +{ + /* + * Copy the minimum of what the user provided and what we actually + * have. + */ + if (copy_to_user(ucmd->ubuffer, ucmd->cmd, + min_t(size_t, ucmd->user_size, kernel_cmd_size))) { + return -EFAULT; + } + return 0; +} /* * Handles a deserialization failure: devices and memory is in unpredictable