fix(kernelmod): page-align ring buffer allocation for non-4K page kernels

[wangrong1069]

vzalloc rounds up to whole pages, but mem_size recorded the raw header+data total. On 16 KiB/64 KiB page kernels the consumer's page-aligned mmap was larger than mem_size and got rejected.

将 ring buffer 分配大小在 vzalloc 前显式按页对齐，使分配请求、
记录的 mem_size 与用户态 mmap 映射大小保持一致，修复非 4K 页
内核上 mmap 报 "size > mem_size" 导致模块不可用的问题。

Log: 修复非4K页内核上mmap大小检查失败
PMS: BUG-374927
Influence: 修复在 Loongson 等非4K页内核上 vfs_monitor 模块 mmap 失败导致服务不可用的问题。

Summary by Sourcery

Bug Fixes:

• Fix ring-buffer mmap failures on kernels with non-4 KiB page sizes by keeping the allocated and reported memory size page-aligned.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Fix ring-buffer mmap failures on kernels with non-4K pages by aligning the allocated and recorded buffer size to PAGE_SIZE, keeping it consistent with the page-aligned userspace mapping.

Sequence diagram for page-aligned ring buffer mmap

sequenceDiagram
    participant Init as vfs_ring_init
    participant Kernel as Kernel memory allocator
    participant User as Userspace consumer

    Init->>Init: PAGE_ALIGN(header_size + data_size)
    Init->>Kernel: vzalloc(alloc_size)
    Kernel-->>Init: ring->mem
    Init->>Init: ring->mem_size = alloc_size
    User->>Init: mmap(page-aligned size)
    Init-->>User: mapping accepted when size <= mem_size

Loading

File-Level Changes

Change	Details	Files
Page-align the ring buffer allocation and recorded size before virtual allocation so kernel and userspace mapping sizes remain consistent.	Compute PAGE_ALIGN(header_size + data_size) as the allocation size. Pass the aligned size to vzalloc and store it in mem_size. Update allocation-failure logging to report the aligned size.	src/kernelmod/vfs_chrdev.c

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: max-lvs, wangrong1069

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• debian/deepin/OWNERS

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[wangrong1069]

/merge