Merge tag 'vfs-7.0-rc1.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs mount updates from Christian Brauner:

 - statmount: accept fd as a parameter

   Extend struct mnt_id_req with a file descriptor field and a new
   STATMOUNT_BY_FD flag. When set, statmount() returns mount information
   for the mount the fd resides on — including detached mounts
   (unmounted via umount2(MNT_DETACH)).

   For detached mounts the STATMOUNT_MNT_POINT and STATMOUNT_MNT_NS_ID
   mask bits are cleared since neither is meaningful. The capability
   check is skipped for STATMOUNT_BY_FD since holding an fd already
   implies prior access to the mount and equivalent information is
   available through fstatfs() and /proc/pid/mountinfo without
   privilege. Includes comprehensive selftests covering both attached
   and detached mount cases.

 - fs: Remove internal old mount API code (1 patch)

   Now that every in-tree filesystem has been converted to the new
   mount API, remove all the legacy shim code in fs_context.c that
   handled unconverted filesystems. This deletes ~280 lines including
   legacy_init_fs_context(), the legacy_fs_context struct, and
   associated wrappers. The mount(2) syscall path for userspace remains
   untouched. Documentation references to the legacy callbacks are
   cleaned up.

 - mount: add OPEN_TREE_NAMESPACE to open_tree()

   Container runtimes currently use CLONE_NEWNS to copy the caller's
   entire mount namespace — only to then pivot_root() and recursively
   unmount everything they just copied. With large mount tables and
   thousands of parallel container launches this creates significant
   contention on the namespace semaphore.

   OPEN_TREE_NAMESPACE copies only the specified mount tree (like
   OPEN_TREE_CLONE) but returns a mount namespace fd instead of a
   detached mount fd. The new namespace contains the copied tree mounted
   on top of a clone of the real rootfs.

   This functions as a combined unshare(CLONE_NEWNS) + pivot_root() in a
   single syscall. Works with user namespaces: an unshare(CLONE_NEWUSER)
   followed by OPEN_TREE_NAMESPACE creates a mount namespace owned by
   the new user namespace. Mount namespace file mounts are excluded from
   the copy to prevent cycles. Includes ~1000 lines of selftests"

* tag 'vfs-7.0-rc1.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  selftests/open_tree: add OPEN_TREE_NAMESPACE tests
  mount: add OPEN_TREE_NAMESPACE
  fs: Remove internal old mount API code
  selftests: statmount: tests for STATMOUNT_BY_FD
  statmount: accept fd as a parameter
  statmount: permission check should return EPERM

4 files changed, 5 insertions, 70 deletions

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 3837891e933d..8025df6e6499 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -180,7 +180,6 @@ prototypes::
 	int (*freeze_fs) (struct super_block *);
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
-	int (*remount_fs) (struct super_block *, int *, char *);
 	void (*umount_begin) (struct super_block *);
 	int (*show_options)(struct seq_file *, struct dentry *);
 	ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
@@ -204,7 +203,6 @@ sync_fs:		read
 freeze_fs:		write
 unfreeze_fs:		write
 statfs:			maybe(read)	(see below)
-remount_fs:		write
 umount_begin:		no
 show_options:		no		(namespace_sem)
 quota_read:		no		(see below)
@@ -229,8 +227,6 @@ file_system_type
 
 prototypes::
 
-	struct dentry *(*mount) (struct file_system_type *, int,
-		       const char *, void *);
 	void (*kill_sb) (struct super_block *);
 
 locking rules:
@@ -238,13 +234,9 @@ locking rules:
 =======		=========
 ops		may block
 =======		=========
-mount		yes
 kill_sb		yes
 =======		=========
 
-->mount() returns ERR_PTR or the root dentry; its superblock should be locked
-on return.
-
 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
 unlocks and drops the reference.
 
diff --git a/Documentation/filesystems/mount_api.rst b/Documentation/filesystems/mount_api.rst
index c99ab1f7fea4..a064234fed5b 100644
--- a/Documentation/filesystems/mount_api.rst
+++ b/Documentation/filesystems/mount_api.rst
@@ -299,8 +299,6 @@ manage the filesystem context.  They are as follows:
      On success it should return 0.  In the case of an error, it should return
      a negative error code.
 
-     .. Note:: reconfigure is intended as a replacement for remount_fs.
-
 
 Filesystem context Security
 ===========================
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index c0f7103628ab..ed3ac56e3c76 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -448,11 +448,8 @@ a file off.
 
 **mandatory**
 
-->get_sb() is gone.  Switch to use of ->mount().  Typically it's just
-a matter of switching from calling ``get_sb_``... to ``mount_``... and changing
-the function type.  If you were doing it manually, just switch from setting
-->mnt_root to some pointer to returning that pointer.  On errors return
-ERR_PTR(...).
+->get_sb() and ->mount() are gone. Switch to using the new mount API. See
+Documentation/filesystems/mount_api.rst for more details.
 
 ---
 
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 85654eb91594..7c753148af88 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -94,11 +94,9 @@ functions:
 
 The passed struct file_system_type describes your filesystem.  When a
 request is made to mount a filesystem onto a directory in your
-namespace, the VFS will call the appropriate mount() method for the
-specific filesystem.  New vfsmount referring to the tree returned by
-->mount() will be attached to the mountpoint, so that when pathname
-resolution reaches the mountpoint it will jump into the root of that
-vfsmount.
+namespace, the VFS will call the appropriate get_tree() method for the
+specific filesystem.  See Documentation/filesystems/mount_api.rst
+for more details.
 
 You can see all filesystems that are registered to the kernel in the
 file /proc/filesystems.
@@ -117,8 +115,6 @@ members are defined:
 		int fs_flags;
 		int (*init_fs_context)(struct fs_context *);
 		const struct fs_parameter_spec *parameters;
-		struct dentry *(*mount) (struct file_system_type *, int,
-			const char *, void *);
 		void (*kill_sb) (struct super_block *);
 		struct module *owner;
 		struct file_system_type * next;
@@ -151,10 +147,6 @@ members are defined:
 	'struct fs_parameter_spec'.
 	More info in Documentation/filesystems/mount_api.rst.
 
-``mount``
-	the method to call when a new instance of this filesystem should
-	be mounted
-
 ``kill_sb``
 	the method to call when an instance of this filesystem should be
 	shut down
@@ -173,45 +165,6 @@ members are defined:
   s_lock_key, s_umount_key, s_vfs_rename_key, s_writers_key,
   i_lock_key, i_mutex_key, invalidate_lock_key, i_mutex_dir_key: lockdep-specific
 
-The mount() method has the following arguments:
-
-``struct file_system_type *fs_type``
-	describes the filesystem, partly initialized by the specific
-	filesystem code
-
-``int flags``
-	mount flags
-
-``const char *dev_name``
-	the device name we are mounting.
-
-``void *data``
-	arbitrary mount options, usually comes as an ASCII string (see
-	"Mount Options" section)
-
-The mount() method must return the root dentry of the tree requested by
-caller.  An active reference to its superblock must be grabbed and the
-superblock must be locked.  On failure it should return ERR_PTR(error).
-
-The arguments match those of mount(2) and their interpretation depends
-on filesystem type.  E.g. for block filesystems, dev_name is interpreted
-as block device name, that device is opened and if it contains a
-suitable filesystem image the method creates and initializes struct
-super_block accordingly, returning its root dentry to caller.
-
-->mount() may choose to return a subtree of existing filesystem - it
-doesn't have to create a new one.  The main result from the caller's
-point of view is a reference to dentry at the root of (sub)tree to be
-attached; creation of new superblock is a common side effect.
-
-The most interesting member of the superblock structure that the mount()
-method fills in is the "s_op" field.  This is a pointer to a "struct
-super_operations" which describes the next level of the filesystem
-implementation.
-
-For more information on mounting (and the new mount API), see
-Documentation/filesystems/mount_api.rst.
-
 The Superblock Object
 =====================
 
@@ -244,7 +197,6 @@ filesystem.  The following members are defined:
 					enum freeze_wholder who);
 		int (*unfreeze_fs) (struct super_block *);
 		int (*statfs) (struct dentry *, struct kstatfs *);
-		int (*remount_fs) (struct super_block *, int *, char *);
 		void (*umount_begin) (struct super_block *);
 
 		int (*show_options)(struct seq_file *, struct dentry *);
@@ -351,10 +303,6 @@ or bottom half).
 ``statfs``
 	called when the VFS needs to get filesystem statistics.
 
-``remount_fs``
-	called when the filesystem is remounted.  This is called with
-	the kernel lock held
-
 ``umount_begin``
 	called when the VFS is unmounting a filesystem.