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Date: Thu, 11 May 2017 13:26:57 -0400
From: Anna Schumaker <Anna.Schumaker@...app.com>
To: David Howells <dhowells@...hat.com>, <mszeredi@...hat.com>,
<viro@...iv.linux.org.uk>, <jlayton@...hat.com>
CC: <linux-fsdevel@...r.kernel.org>, <linux-nfs@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 00/14] VFS: Introduce superblock configuration
context [ver #2]
Hi David,
On 05/11/2017 09:59 AM, David Howells wrote:
>
> Here are a set of patches to create a superblock configuration context
> prior to setting up a new mount, populating it with the parsed
> options/binary data, creating the superblock and then effecting the mount.
>
> This allows namespaces and other information to be conveyed through the
> mount procedure. It also allows extra error information to be returned
> (so many things can go wrong during a mount that a small integer isn't
> really sufficient to convey the issue).
>
> This also allows Miklós Szeredi's idea of doing:
>
> fd = fsopen("nfs");
> write(fd, "option=val", ...);
> fsmount(fd, "/mnt");
>
> that he presented at LSF-2017 to be implemented (see the relevant patches
> in the series), to which I can add:
>
> read(fd, error_buffer, ...);
>
> to read back any error message. I didn't use netlink as that would make it
> depend on CONFIG_NET and would introduce network namespacing issues.
>
> I've implemented mount context handling for procfs and nfs.
>
> Significant changes:
>
> ver #2:
>
> (*) Removed the ->fill_super() from sb_config_operations and passed it in
> directly to functions that want to call it. NFS now calls
> nfs_fill_super() directly rather than jumping through a pointer to it
> since there's only the one option at the moment.
>
> (*) Removed ->mnt_ns and ->sb from sb_config and moved ->pid_ns into
> proc_sb_config.
>
> (*) Renamed create_super -> get_tree.
>
> (*) Renamed struct mount_context to struct sb_config and amended various
> variable names.
>
> (*) sys_fsmount() acquired AT_* flags and MS_* flags (for MNT_* flags)
> arguments.
>
> ver #1:
>
> (*) Split the sb_config stuff out into its own header.
>
> (*) Support non-context aware filesystems through a special set of
> sb_config operations.
>
> (*) Stored the created superblock and root dentry into the sb_config after
> creation rather than directly into a vfsmount. This allows some
> arguments to be removed to various NFS functions.
>
> (*) Added an explicit superblock-creation step. This allows a created
> superblock to then be mounted multiple times.
>
> (*) Added a flag to say that the sb_config is degraded and cannot have
> another go at having a superblock creation whilst getting rid of the
> one that says it's already mounted.
>
> Further developments:
>
> (*) Implement sb reconfiguration (for now it returns ENOANO).
>
> (*) Implement mount context support in more filesystems, ext4 being next
> on my list.
>
> (*) Move the walk-from-root stuff that nfs has to generic code so that you
> can do something akin to:
>
> mount /dev/sda1:/foo/bar /mnt
>
> See nfs_follow_remote_path() and mount_subtree(). This is slightly
> tricky in NFS as we have to prevent referral loops.
>
> (*) Move the pid_ns pointer from struct mount_context to struct
> proc_mount_context as I'm not sure it's necessary for anything other
> than procfs.
>
> (*) Work out how to get at the error message incurred by submounts
> encountered during nfs_follow_remote_path().
>
> Should the error message be moved to task_struct and made more
> general, perhaps retrieved with a prctl() function?
>
> (*) Clean up/consolidate the security functions. Possibly add a
> validation hook to be called at the same time as the mount context
> validate op.
>
> The patches can be found here also:
>
> http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=mount-context
>
> David
> ---
> David Howells (14):
> Provide a function to create a NUL-terminated string from unterminated data
> Clean up whitespace in fs/namespace.c
> VFS: Make get_mnt_ns() return the namespace
> VFS: Make get_filesystem() return the affected filesystem
> VFS: Provide empty name qstr
> VFS: Introduce a superblock configuration context
> Implement fsopen() to prepare for a mount
> Implement fsmount() to effect a pre-configured mount
> Sample program for driving fsopen/fsmount
> procfs: Move proc_fill_super() to fs/proc/root.c
> proc: Add superblock config support to procfs
> NFS: Add mount context support.
> Support legacy filesystems
> Add commands to create or update a superblock
>
>
> Documentation/filesystems/mounting.txt | 470 ++++++++
> arch/x86/entry/syscalls/syscall_32.tbl | 2
> arch/x86/entry/syscalls/syscall_64.tbl | 2
> fs/Makefile | 3
> fs/dcache.c | 8
> fs/filesystems.c | 3
> fs/fsopen.c | 302 +++++
> fs/gfs2/dir.c | 3
> fs/internal.h | 4
> fs/libfs.c | 17
> fs/mount.h | 3
> fs/namei.c | 3
> fs/namespace.c | 495 +++++++--
> fs/nfs/Makefile | 2
> fs/nfs/client.c | 74 +
> fs/nfs/getroot.c | 76 +
> fs/nfs/internal.h | 142 +--
> fs/nfs/mount.c | 1497 +++++++++++++++++++++++++++
> fs/nfs/namespace.c | 76 +
> fs/nfs/nfs3_fs.h | 2
> fs/nfs/nfs3client.c | 6
> fs/nfs/nfs3proc.c | 2
> fs/nfs/nfs4_fs.h | 4
> fs/nfs/nfs4client.c | 82 +
> fs/nfs/nfs4namespace.c | 208 ++--
> fs/nfs/nfs4proc.c | 3
> fs/nfs/nfs4super.c | 220 ++--
> fs/nfs/proc.c | 2
> fs/nfs/super.c | 1782 ++------------------------------
> fs/nsfs.c | 3
> fs/pipe.c | 3
> fs/proc/inode.c | 50 -
> fs/proc/internal.h | 6
> fs/proc/root.c | 210 +++-
> fs/sb_config.c | 524 +++++++++
> fs/super.c | 110 +-
> include/linux/dcache.h | 5
> include/linux/fs.h | 16
> include/linux/lsm_hooks.h | 47 +
> include/linux/mount.h | 4
> include/linux/nfs_xdr.h | 7
> include/linux/sb_config.h | 100 ++
> include/linux/security.h | 40 +
> include/linux/string.h | 1
> include/linux/syscalls.h | 3
> include/uapi/linux/magic.h | 1
> kernel/sys_ni.c | 4
> mm/util.c | 24
> samples/fsmount/test-fsmount.c | 79 +
> security/security.c | 45 +
> security/selinux/hooks.c | 202 +++-
> 51 files changed, 4596 insertions(+), 2381 deletions(-)
Is there any way to split the NFS patch into multiple pieces? The patch in your git tree is longer than my attention span, and I'm having a hard time keeping track of everything going on. I also suspect that this might be why it doesn't show up in my email with the rest of your patches.
Thanks,
Anna
> create mode 100644 Documentation/filesystems/mounting.txt
> create mode 100644 fs/fsopen.c
> create mode 100644 fs/nfs/mount.c
> create mode 100644 fs/sb_config.c
> create mode 100644 include/linux/sb_config.h
> create mode 100644 samples/fsmount/test-fsmount.c
>
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