linux-kernel - Re: [PATCH v4 0/6] querying mount attributes

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Message-ID: <374433e3-ab72-64a3-0fa0-ab455268e5e0@themaw.net>
Date:   Wed, 1 Nov 2023 19:52:45 +0800
From:   Ian Kent <raven@...maw.net>
To:     Miklos Szeredi <mszeredi@...hat.com>, linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-man@...r.kernel.org, linux-security-module@...r.kernel.org,
        Karel Zak <kzak@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        Matthew House <mattlloydhouse@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v4 0/6] querying mount attributes

On 25/10/23 22:01, Miklos Szeredi wrote:
> Implement mount querying syscalls agreed on at LSF/MM 2023.
>
> Features:
>
>   - statx-like want/got mask
>   - allows returning ascii strings (fs type, root, mount point)
>   - returned buffer is relocatable (no pointers)
>
> Still missing:
>   - man pages
>   - kselftest
>
> Please find the test utility at the end of this mail.
>
>    Usage: statmnt [-l|-r] [-u] (mnt_id|path)
>
> Git tree:
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git#statmount-v4
>
>
> Changes v3..v4:
>
>   - incorporate patch moving list of mounts to an rbtree
>   - wire up syscalls for all archs
>   - add LISTMOUNT_RECURSIVE (depth first iteration of mount tree)
>   - add LSMT_ROOT (list root instead of a specific mount ID)
>   - list_for_each_entry_del() moved to a separate patchset
>
> Changes v1..v3:
>
>   - rename statmnt(2) -> statmount(2)
>   - rename listmnt(2) -> listmount(2)
>   - make ABI 32bit compatible by passing 64bit args in a struct (tested on
>     i386 and x32)
>   - only accept new 64bit mount IDs
>   - fix compile on !CONFIG_PROC_FS
>   - call security_sb_statfs() in both syscalls
>   - make lookup_mnt_in_ns() static
>   - add LISTMOUNT_UNREACHABLE flag to listmnt() to explicitly ask for
>     listing unreachable mounts
>   - remove .sb_opts
>   - remove subtype from .fs_type
>   - return the number of bytes used (including strings) in .size
>   - rename .mountpoint -> .mnt_point
>   - point strings by an offset against char[] VLA at the end of the struct.
>     E.g. printf("fs_type: %s\n", st->str + st->fs_type);
>   - don't save string lengths
>   - extend spare space in struct statmnt (complete size is now 512 bytes)
>
>
> Miklos Szeredi (6):
>    add unique mount ID
>    mounts: keep list of mounts in an rbtree
>    namespace: extract show_path() helper
>    add statmount(2) syscall
>    add listmount(2) syscall
>    wire up syscalls for statmount/listmount
>
>   arch/alpha/kernel/syscalls/syscall.tbl      |   3 +
>   arch/arm/tools/syscall.tbl                  |   3 +
>   arch/arm64/include/asm/unistd32.h           |   4 +
>   arch/ia64/kernel/syscalls/syscall.tbl       |   3 +
>   arch/m68k/kernel/syscalls/syscall.tbl       |   3 +
>   arch/microblaze/kernel/syscalls/syscall.tbl |   3 +
>   arch/mips/kernel/syscalls/syscall_n32.tbl   |   3 +
>   arch/mips/kernel/syscalls/syscall_n64.tbl   |   3 +
>   arch/mips/kernel/syscalls/syscall_o32.tbl   |   3 +
>   arch/parisc/kernel/syscalls/syscall.tbl     |   3 +
>   arch/powerpc/kernel/syscalls/syscall.tbl    |   3 +
>   arch/s390/kernel/syscalls/syscall.tbl       |   3 +
>   arch/sh/kernel/syscalls/syscall.tbl         |   3 +
>   arch/sparc/kernel/syscalls/syscall.tbl      |   3 +
>   arch/x86/entry/syscalls/syscall_32.tbl      |   3 +
>   arch/x86/entry/syscalls/syscall_64.tbl      |   2 +
>   arch/xtensa/kernel/syscalls/syscall.tbl     |   3 +
>   fs/internal.h                               |   2 +
>   fs/mount.h                                  |  27 +-
>   fs/namespace.c                              | 573 ++++++++++++++++----
>   fs/pnode.c                                  |   2 +-
>   fs/proc_namespace.c                         |  13 +-
>   fs/stat.c                                   |   9 +-
>   include/linux/mount.h                       |   5 +-
>   include/linux/syscalls.h                    |   8 +
>   include/uapi/asm-generic/unistd.h           |   8 +-
>   include/uapi/linux/mount.h                  |  65 +++
>   include/uapi/linux/stat.h                   |   1 +
>   28 files changed, 635 insertions(+), 129 deletions(-)

Looks ok to me,covers the primary cases I needed when I worked

on using fsinfo() in systemd.


Karel, is there anything missing you would need for adding

libmount support?


Reviewed-by: Ian Kent <raven@...maw.net>


>