Re: [RFC][PATCH 00/14] VFS: Introduce superblock configuration context [ver #2]

[Anna Schumaker]

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 MiklÃs 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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