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Message-ID: <mafs0pl97xwj0.fsf@kernel.org>
Date: Mon, 24 Nov 2025 16:47:31 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Pasha Tatashin <pasha.tatashin@...een.com>, jasonmiu@...gle.com,
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Subject: Re: [PATCH v7 06/22] liveupdate: luo_file: implement file systems
callbacks
Hi Pasha,
Sorry, I accidentally sent this without trimming the context first.
Below is the version with the relevant bits:
On Sat, Nov 22 2025, Pasha Tatashin wrote:
> This patch implements the core mechanism for managing preserved
> files throughout the live update lifecycle. It provides the logic to
> invoke the file handler callbacks (preserve, unpreserve, freeze,
> unfreeze, retrieve, and finish) at the appropriate stages.
>
> During the reboot phase, luo_file_freeze() serializes the final
> metadata for each file (handler compatible string, token, and data
> handle) into a memory region preserved by KHO. In the new kernel,
> luo_file_deserialize() reconstructs the in-memory file list from this
> data, preparing the session for retrieval.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> ---
> include/linux/kho/abi/luo.h | 39 +-
> include/linux/liveupdate.h | 98 ++++
> kernel/liveupdate/Makefile | 1 +
> kernel/liveupdate/luo_file.c | 882 +++++++++++++++++++++++++++++++
> kernel/liveupdate/luo_internal.h | 38 ++
> 5 files changed, 1057 insertions(+), 1 deletion(-)
> create mode 100644 kernel/liveupdate/luo_file.c
>
> diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
> index a2d2940eca6b..fc143f243871 100644
> --- a/include/linux/kho/abi/luo.h
> +++ b/include/linux/kho/abi/luo.h
> @@ -65,6 +65,11 @@
> * Metadata for a single session, including its name and a physical pointer
> * to another preserved memory block containing an array of
> * `struct luo_file_ser` for all files in that session.
> + *
> + * - struct luo_file_ser:
> + * Metadata for a single preserved file. Contains the `compatible` string to
> + * find the correct handler in the new kernel, a user-provided `token` for
> + * identification, and an opaque `data` handle for the handler to use.
> */
>
> #ifndef _LINUX_KHO_ABI_LUO_H
> @@ -82,13 +87,43 @@
> #define LUO_FDT_COMPATIBLE "luo-v1"
> #define LUO_FDT_LIVEUPDATE_NUM "liveupdate-number"
>
> +#define LIVEUPDATE_HNDL_COMPAT_LENGTH 48
> +
> +/**
> + * struct luo_file_ser - Represents the serialized preserves files.
> + * @compatible: File handler compatible string.
> + * @data: Private data
> + * @token: User provided token for this file
> + *
> + * If this structure is modified, LUO_SESSION_COMPATIBLE must be updated.
> + */
> +struct luo_file_ser {
> + char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
> + u64 data;
> + u64 token;
> +} __packed;
> +
> +/**
> + * struct luo_file_set_ser - Represents the serialized metadata for file set
> + * @files: The physical address of a contiguous memory block that holds
> + * the serialized state of files (array of luo_file_ser) in this file
> + * set.
> + * @count: The total number of files that were part of this session during
> + * serialization. Used for iteration and validation during
> + * restoration.
> + */
> +struct luo_file_set_ser {
> + u64 files;
> + u64 count;
> +} __packed;
The change to using file_set looks a lot nicer than what the previous
version was doing!
> +
> /*
> * LUO FDT session node
> * LUO_FDT_SESSION_HEADER: is a u64 physical address of struct
> * luo_session_header_ser
> */
> #define LUO_FDT_SESSION_NODE_NAME "luo-session"
> -#define LUO_FDT_SESSION_COMPATIBLE "luo-session-v1"
> +#define LUO_FDT_SESSION_COMPATIBLE "luo-session-v2"
> #define LUO_FDT_SESSION_HEADER "luo-session-header"
>
> /**
[...]
> +int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
> +{
> + struct liveupdate_file_op_args args = {0};
> + struct liveupdate_file_handler *fh;
> + struct luo_file *luo_file;
> + struct file *file;
> + int err;
> +
> + if (luo_token_is_used(file_set, token))
> + return -EEXIST;
> +
> + file = fget(fd);
> + if (!file)
> + return -EBADF;
> +
> + err = luo_alloc_files_mem(file_set);
> + if (err)
> + goto err_files_mem;
Nit: ^^ two spaces here.
> +
> + if (file_set->count == LUO_FILE_MAX) {
> + err = -ENOSPC;
> + goto err_files_mem;
> + }
> +
> + err = -ENOENT;
> + luo_list_for_each_private(fh, &luo_file_handler_list, list) {
> + if (fh->ops->can_preserve(fh, file)) {
> + err = 0;
> + break;
> + }
> + }
> +
[...]
> +int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> +{
> + struct liveupdate_file_handler *fh_iter;
> + int err;
> +
> + if (!liveupdate_enabled())
> + return -EOPNOTSUPP;
> +
> + /* Sanity check that all required callbacks are set */
> + if (!fh->ops->preserve || !fh->ops->unpreserve ||
> + !fh->ops->retrieve || !fh->ops->finish) {
You are still missing a check for can_preserve() here. It is a mandatory
callback and luo_preserve_file() calls it without checking for NULL.
With these and Mike's comments addressed,
Reviewed-by: Pratyush Yadav <pratyush@...nel.org>
> + return -EINVAL;
> + }
> +
[...]
--
Regards,
Pratyush Yadav
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