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* [PATCH v2 0/2] New mount API syscalls
@ 2020-02-07 17:42 Petr Vorel
  2020-02-07 17:42 ` [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2) Petr Vorel
  2020-02-07 17:42 ` [PATCH v2 2/2] Add manpage for fsopen(2), fspick(2) and fsmount(2) Petr Vorel
  0 siblings, 2 replies; 4+ messages in thread
From: Petr Vorel @ 2020-02-07 17:42 UTC (permalink / raw)
  To: linux-man
  Cc: Petr Vorel, David Howells, Michael Kerrisk, Zorro Lang,
	linux-fsdevel, linux-kernel

Hi David, Michael,

looks like David's patches to add new mount API syscalls, so I dared to
resent them. I've just changed kernel version to 5.2, fixed typos in
flags and added my tags. + added some questions in patches themselves.

Feel free to send final version in v3.

Kind regards,
Petr

David Howells (2):
  Add manpages for move_mount(2) and open_tree(2)
  Add manpage for fsopen(2), fspick(2) and fsmount(2)

 man2/fsconfig.2   | 282 ++++++++++++++++++++++++++++++++++++++++++++++
 man2/fsmount.2    |   1 +
 man2/fsopen.2     | 256 +++++++++++++++++++++++++++++++++++++++++
 man2/fspick.2     | 195 ++++++++++++++++++++++++++++++++
 man2/move_mount.2 | 271 ++++++++++++++++++++++++++++++++++++++++++++
 man2/open_tree.2  | 260 ++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 1265 insertions(+)
 create mode 100644 man2/fsconfig.2
 create mode 100644 man2/fsmount.2
 create mode 100644 man2/fsopen.2
 create mode 100644 man2/fspick.2
 create mode 100644 man2/move_mount.2
 create mode 100644 man2/open_tree.2

-- 
2.24.1


^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2)
  2020-02-07 17:42 [PATCH v2 0/2] New mount API syscalls Petr Vorel
@ 2020-02-07 17:42 ` Petr Vorel
  2020-02-26 11:48   ` Petr Vorel
  2020-02-07 17:42 ` [PATCH v2 2/2] Add manpage for fsopen(2), fspick(2) and fsmount(2) Petr Vorel
  1 sibling, 1 reply; 4+ messages in thread
From: Petr Vorel @ 2020-02-07 17:42 UTC (permalink / raw)
  To: linux-man
  Cc: David Howells, Michael Kerrisk, Zorro Lang, linux-fsdevel,
	linux-kernel, Petr Vorel

From: David Howells <dhowells@redhat.com>

Add manual pages to document the move_mount and open_tree() system calls.

Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
Hi,

* man2/move_mount.2
fixed MOVE_MOUNT_F_NO_AUTOMOUNT => MOVE_MOUNT_F_AUTOMOUNTS
and MOVE_MOUNT_T_NO_AUTOMOUNT => MOVE_MOUNT_T_AUTOMOUNTS
maybe mention -EPERM on !may_mount() ?

* man2/open_tree.2
maybe mention -EPERM on (detached && !may_mount()) ?

Kind regards,
Petr

 man2/move_mount.2 | 271 ++++++++++++++++++++++++++++++++++++++++++++++
 man2/open_tree.2  | 260 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 531 insertions(+)
 create mode 100644 man2/move_mount.2
 create mode 100644 man2/open_tree.2

diff --git a/man2/move_mount.2 b/man2/move_mount.2
new file mode 100644
index 000000000..bca352ad3
--- /dev/null
+++ b/man2/move_mount.2
@@ -0,0 +1,271 @@
+'\" t
+.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH MOVE_MOUNT 2 2019-10-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+move_mount \- Move mount objects around the filesystem topology
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/mount.h>
+.br
+.B #include <unistd.h>
+.br
+.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
+.PP
+.BI "int move_mount(int " from_dirfd ", const char *" from_pathname ","
+.BI "               int " to_dirfd ", const char *" to_pathname ","
+.BI "               unsigned int " flags );
+.fi
+.PP
+.IR Note :
+There is no glibc wrapper for this system call.
+.SH DESCRIPTION
+The
+.BR move_mount ()
+call moves a mount from one place to another; it can also be used to attach an
+unattached mount created by
+.BR fsmount "() or " open_tree "() with " OPEN_TREE_CLONE .
+.PP
+If
+.BR move_mount ()
+is called repeatedly with a file descriptor that refers to a mount object,
+then the object will be attached/moved the first time and then moved again and
+again and again, detaching it from the previous mountpoint each time.
+.PP
+To access the source mount object or the destination mountpoint, no
+permissions are required on the object itself, but if either pathname is
+supplied, execute (search) permission is required on all of the directories
+specified in
+.IR from_pathname " or " to_pathname .
+.PP
+The caller does, however, require the appropriate capabilities or permission
+to effect a mount.
+.PP
+.BR move_mount ()
+uses
+.IR from_pathname ", " from_dirfd " and part of " flags
+to locate the mount object to be moved and
+.IR to_pathname ", " to_dirfd " and another part of " flags
+to locate the destination mountpoint.  Each lookup can be done in one of a
+variety of ways:
+.TP
+[*] By absolute path.
+The pathname points to an absolute path and the dirfd is ignored.  The file is
+looked up by name, starting from the root of the filesystem as seen by the
+calling process.
+.TP
+[*] By cwd-relative path.
+The pathname points to a relative path and the dirfd is
+.IR AT_FDCWD .
+The file is looked up by name, starting from the current working directory.
+.TP
+[*] By dir-relative path.
+The pathname points to relative path and the dirfd indicates a file descriptor
+pointing to a directory.  The file is looked up by name, starting from the
+directory specified by
+.IR dirfd .
+.TP
+[*] By file descriptor.
+The pathname points to "", the dirfd points directly to the mount object to
+move or the destination mount point and the appropriate
+.B *_EMPTY_PATH
+flag is set.
+.PP
+.I flags
+can be used to influence a path-based lookup.  A value for
+.I flags
+is constructed by OR'ing together zero or more of the following constants:
+.TP
+.BR MOVE_MOUNT_F_EMPTY_PATH
+.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
+If
+.I from_pathname
+is an empty string, operate on the file referred to by
+.IR from_dirfd
+(which may have been obtained using the
+.BR open (2)
+.B O_PATH
+flag or
+.BR open_tree ()).
+If
+.I from_dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+In this case,
+.I from_dirfd
+can refer to any type of file, not just a directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.B MOVE_MOUNT_T_EMPTY_PATH
+As above, but operating on
+.IR to_pathname " and " to_dirfd .
+.TP
+.B MOVE_MOUNT_F_AUTOMOUNTS
+Don't automount the terminal ("basename") component of
+.I from_pathname
+if it is a directory that is an automount point.  This allows a mount object
+that has an automount point at its root to be moved and prevents unintended
+triggering of an automount point.
+The
+.B MOVE_MOUNT_F_AUTOMOUNTS
+flag has no effect if the automount point has already been mounted over.
+.TP
+.B MOVE_MOUNT_T_AUTOMOUNTS
+As above, but operating on
+.IR to_pathname " and " to_dirfd .
+This allows an automount point to be manually mounted over.
+.TP
+.B MOVE_MOUNT_F_SYMLINKS
+If
+.I from_pathname
+is a symbolic link, then dereference it.  The default for
+.BR move_mount ()
+is to not follow symlinks.
+.TP
+.B MOVE_MOUNT_T_SYMLINKS
+As above, but operating on
+.IR to_pathname " and " to_dirfd .
+
+.SH EXAMPLES
+The
+.BR move_mount ()
+function can be used like the following:
+.PP
+.RS
+.nf
+move_mount(AT_FDCWD, "/a", AT_FDCWD, "/b", 0);
+.fi
+.RE
+.PP
+This would move the object mounted on "/a" to "/b".  It can also be used in
+conjunction with
+.BR open_tree "(2) or " open "(2) with " O_PATH :
+.PP
+.RS
+.nf
+fd = open_tree(AT_FDCWD, "/mnt", 0);
+move_mount(fd, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
+move_mount(fd, "", AT_FDCWD, "/mnt3", MOVE_MOUNT_F_EMPTY_PATH);
+move_mount(fd, "", AT_FDCWD, "/mnt4", MOVE_MOUNT_F_EMPTY_PATH);
+.fi
+.RE
+.PP
+This would attach the path point for "/mnt" to fd, then it would move the
+mount to "/mnt2", then move it to "/mnt3" and finally to "/mnt4".
+.PP
+It can also be used to attach new mounts:
+.PP
+.RS
+.nf
+sfd = fsopen("ext4", FSOPEN_CLOEXEC);
+fsconfig(sfd, FSCONFIG_SET_STRING, "source", "/dev/sda1", 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
+fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+mfd = fsmount(sfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_NODEV);
+move_mount(mfd, "", AT_FDCWD, "/home", MOVE_MOUNT_F_EMPTY_PATH);
+.fi
+.RE
+.PP
+Which would open the Ext4 filesystem mounted on "/dev/sda1", turn on user
+extended attribute support and create a mount object for it.  Finally, the new
+mount object would be attached with
+.BR move_mount ()
+to "/home".
+
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, 0 is returned.  On error, \-1 is returned, and
+.I errno
+is set appropriately.
+.SH ERRORS
+.TP
+.B EACCES
+Search permission is denied for one of the directories
+in the path prefix of
+.IR pathname .
+(See also
+.BR path_resolution (7).)
+.TP
+.B EBADF
+.IR from_dirfd " or " to_dirfd
+is not a valid open file descriptor.
+.TP
+.B EFAULT
+.IR from_pathname " or " to_pathname
+is NULL or either one point to a location outside the process's accessible
+address space.
+.TP
+.B EINVAL
+Reserved flag specified in
+.IR flags .
+.TP
+.B ELOOP
+Too many symbolic links encountered while traversing the pathname.
+.TP
+.B ENAMETOOLONG
+.IR from_pathname " or " to_pathname
+is too long.
+.TP
+.B ENOENT
+A component of
+.IR from_pathname " or " to_pathname
+does not exist, or one is an empty string and the appropriate
+.B *_EMPTY_PATH
+was not specified in
+.IR flags .
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.TP
+.B ENOTDIR
+A component of the path prefix of
+.IR from_pathname " or " to_pathname
+is not a directory or one or the other is relative and the appropriate
+.I *_dirfd
+is a file descriptor referring to a file other than a directory.
+.SH VERSIONS
+.BR move_mount ()
+was added to Linux in kernel 5.2.
+.SH CONFORMING TO
+.BR move_mount ()
+is Linux-specific.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR move_mount ()
+system call; call it using
+.BR syscall (2).
+.SH SEE ALSO
+.BR fsmount (2),
+.BR fsopen (2),
+.BR open_tree (2)
diff --git a/man2/open_tree.2 b/man2/open_tree.2
new file mode 100644
index 000000000..56783898f
--- /dev/null
+++ b/man2/open_tree.2
@@ -0,0 +1,260 @@
+'\" t
+.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH OPEN_TREE 2 2019-10-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+open_tree \- Pick or clone mount object and attach to fd
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/mount.h>
+.br
+.B #include <unistd.h>
+.br
+.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
+.PP
+.BI "int open_tree(int " dirfd ", const char *" pathname ", unsigned int " flags );
+.fi
+.PP
+.IR Note :
+There are no glibc wrappers for these system calls.
+.SH DESCRIPTION
+.BR open_tree ()
+picks the mount object specified by the pathname and attaches it to a new file
+descriptor or clones it and attaches the clone to the file descriptor.  The
+resultant file descriptor is indistinguishable from one produced by
+.BR open "(2) with " O_PATH .
+.PP
+In the case that the mount object is cloned, the clone will be "unmounted" and
+destroyed when the file descriptor is closed if it is not otherwise mounted
+somewhere by calling
+.BR move_mount (2).
+.PP
+To select a mount object, no permissions are required on the object referred
+to by the path, but execute (search) permission is required on all of the
+directories in
+.I pathname
+that lead to the object.
+.PP
+To clone an object, however, the caller must have mount capabilities and
+permissions.
+.PP
+.BR open_tree ()
+uses
+.IR pathname ", " dirfd " and " flags
+to locate the target object in one of a variety of ways:
+.TP
+[*] By absolute path.
+.I pathname
+points to an absolute path and
+.I dirfd
+is ignored.  The object is looked up by name, starting from the root of the
+filesystem as seen by the calling process.
+.TP
+[*] By cwd-relative path.
+.I pathname
+points to a relative path and
+.IR dirfd " is " AT_FDCWD .
+The object is looked up by name, starting from the current working directory.
+.TP
+[*] By dir-relative path.
+.I pathname
+points to relative path and
+.I dirfd
+indicates a file descriptor pointing to a directory.  The object is looked up
+by name, starting from the directory specified by
+.IR dirfd .
+.TP
+[*] By file descriptor.
+.I pathname
+is "",
+.I dirfd
+indicates a file descriptor and
+.B AT_EMPTY_PATH
+is set in
+.IR flags .
+The mount attached to the file descriptor is queried directly.  The file
+descriptor may point to any type of file, not just a directory.
+
+.\"______________________________________________________________
+.PP
+.I flags
+can be used to control the operation of the function and to influence a
+path-based lookup.  A value for
+.I flags
+is constructed by OR'ing together zero or more of the following constants:
+.TP
+.BR AT_EMPTY_PATH
+.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
+If
+.I pathname
+is an empty string, operate on the file referred to by
+.IR dirfd
+(which may have been obtained from
+.BR open "(2) with"
+.BR O_PATH ", from " fsmount (2)
+or from another
+.BR open_tree ()).
+If
+.I dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+In this case,
+.I dirfd
+can refer to any type of file, not just a directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.BR AT_NO_AUTOMOUNT
+Don't automount the terminal ("basename") component of
+.I pathname
+if it is a directory that is an automount point.  This flag allows the
+automount point itself to be picked up or a mount cloned that is rooted on the
+automount point.  The
+.B AT_NO_AUTOMOUNT
+flag has no effect if the mount point has already been mounted over.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.B AT_SYMLINK_NOFOLLOW
+If
+.I pathname
+is a symbolic link, do not dereference it: instead pick up or clone a mount
+rooted on the link itself.
+.TP
+.B OPEN_TREE_CLOEXEC
+Set the close-on-exec flag for the new file descriptor.  This will cause the
+file descriptor to be closed automatically when a process exec's.
+.TP
+.B OPEN_TREE_CLONE
+Rather than directly attaching the selected object to the file descriptor,
+clone the object, set the root of the new mount object to that point and
+attach the clone to the file descriptor.
+.TP
+.B AT_RECURSIVE
+This is only permitted in conjunction with OPEN_TREE_CLONE.  It causes the
+entire mount subtree rooted at the selected spot to be cloned rather than just
+that one mount object.
+
+
+.SH EXAMPLE
+The
+.BR open_tree ()
+function can be used like the following:
+.PP
+.RS
+.nf
+fd1 = open_tree(AT_FDCWD, "/mnt", 0);
+fd2 = open_tree(fd1, "",
+                AT_EMPTY_PATH | OPEN_TREE_CLONE | AT_RECURSIVE);
+move_mount(fd2, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
+.fi
+.RE
+.PP
+This would attach the path point for "/mnt" to fd1, then it would copy the
+entire subtree at the point referred to by fd1 and attach that to fd2; lastly,
+it would attach the clone to "/mnt2".
+
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, the new file descriptor is returned.  On error, \-1 is returned,
+and
+.I errno
+is set appropriately.
+.SH ERRORS
+.TP
+.B EACCES
+Search permission is denied for one of the directories
+in the path prefix of
+.IR pathname .
+(See also
+.BR path_resolution (7).)
+.TP
+.B EBADF
+.I dirfd
+is not a valid open file descriptor.
+.TP
+.B EFAULT
+.I pathname
+is NULL or
+.IR pathname
+point to a location outside the process's accessible address space.
+.TP
+.B EINVAL
+Reserved flag specified in
+.IR flags .
+.TP
+.B ELOOP
+Too many symbolic links encountered while traversing the pathname.
+.TP
+.B ENAMETOOLONG
+.I pathname
+is too long.
+.TP
+.B ENOENT
+A component of
+.I pathname
+does not exist, or
+.I pathname
+is an empty string and
+.B AT_EMPTY_PATH
+was not specified in
+.IR flags .
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.TP
+.B ENOTDIR
+A component of the path prefix of
+.I pathname
+is not a directory or
+.I pathname
+is relative and
+.I dirfd
+is a file descriptor referring to a file other than a directory.
+.SH VERSIONS
+.BR open_tree ()
+was added to Linux in kernel 5.2.
+.SH CONFORMING TO
+.BR open_tree ()
+is Linux-specific.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR open_tree ()
+system call; call it using
+.BR syscall (2).
+.SH SEE ALSO
+.BR fsmount (2),
+.BR move_mount (2),
+.BR open (2)
-- 
2.24.1


^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH v2 2/2] Add manpage for fsopen(2), fspick(2) and fsmount(2)
  2020-02-07 17:42 [PATCH v2 0/2] New mount API syscalls Petr Vorel
  2020-02-07 17:42 ` [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2) Petr Vorel
@ 2020-02-07 17:42 ` Petr Vorel
  1 sibling, 0 replies; 4+ messages in thread
From: Petr Vorel @ 2020-02-07 17:42 UTC (permalink / raw)
  To: linux-man
  Cc: David Howells, Michael Kerrisk, Zorro Lang, linux-fsdevel,
	linux-kernel, Petr Vorel

From: David Howells <dhowells@redhat.com>

Add a manual page to document the fsopen(), fspick() and fsmount() system
calls.

Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
Hi,

* man2/fsmount.2
maybe document these flags?
#define MOUNT_ATTR_RDONLY      0x00000001 /* Mount read-only */
#define MOUNT_ATTR_NOSUID      0x00000002 /* Ignore suid and sgid bits */
#define MOUNT_ATTR_NODEV       0x00000004 /* Disallow access to device special files */
#define MOUNT_ATTR_NOEXEC      0x00000008 /* Disallow program execution */
#define MOUNT_ATTR__ATIME      0x00000070 /* Setting on how atime should be updated */
#define MOUNT_ATTR_RELATIME    0x00000000 /* - Update atime relative to mtime/ctime. */
#define MOUNT_ATTR_NOATIME     0x00000010 /* - Do not update access times. */
#define MOUNT_ATTR_STRICTATIME 0x00000020 /* - Always perform atime updates */
#define MOUNT_ATTR_NODIRATIME  0x00000080 /* Do not update directory access times */

* man2/fsopen.2
and these?
enum fs_context_phase {
	FS_CONTEXT_CREATE_PARAMS,	/* Loading params for sb creation */
	FS_CONTEXT_CREATING,		/* A superblock is being created */
	FS_CONTEXT_AWAITING_MOUNT,	/* Superblock created, awaiting fsmount() */
	FS_CONTEXT_AWAITING_RECONF,	/* Awaiting initialisation for reconfiguration */
	FS_CONTEXT_RECONF_PARAMS,	/* Loading params for reconfiguration */
	FS_CONTEXT_RECONFIGURING,	/* Reconfiguring the superblock */
	FS_CONTEXT_FAILED,		/* Failed to correctly transition a context */
};


Kind regards,
Petr

 man2/fsconfig.2 | 282 ++++++++++++++++++++++++++++++++++++++++++++++++
 man2/fsmount.2  |   1 +
 man2/fsopen.2   | 256 +++++++++++++++++++++++++++++++++++++++++++
 man2/fspick.2   | 195 +++++++++++++++++++++++++++++++++
 4 files changed, 734 insertions(+)
 create mode 100644 man2/fsconfig.2
 create mode 100644 man2/fsmount.2
 create mode 100644 man2/fsopen.2
 create mode 100644 man2/fspick.2

diff --git a/man2/fsconfig.2 b/man2/fsconfig.2
new file mode 100644
index 000000000..93b82997a
--- /dev/null
+++ b/man2/fsconfig.2
@@ -0,0 +1,282 @@
+'\" t
+.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH FSCONFIG 2 2019-10-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+fsconfig \- Filesystem parameterisation
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/mount.h>
+.br
+.B #include <unistd.h>
+.br
+.B #include <sys/mount.h>
+.PP
+.BI "int fsconfig(int *" fd ", unsigned int " cmd ", const char *" key ,
+.br
+.BI "             const void __user *" value ", int " aux ");"
+.br
+.BI
+.fi
+.PP
+.IR Note :
+There is no glibc wrapper for this system call.
+.SH DESCRIPTION
+.PP
+.BR fsconfig ()
+is used to supply parameters to and issue commands against a filesystem
+configuration context as set up by
+.BR fsopen (2)
+or
+.BR fspick (2).
+The context is supplied attached to the file descriptor specified by
+.I fd
+argument.
+.PP
+The
+.I cmd
+argument indicates the command to be issued, where some of the commands simply
+supply parameters to the context.  The meaning of
+.IR key ", " value " and " aux
+are command-dependent; unless required for the command, these should be set to
+NULL or 0.
+.PP
+The available commands are:
+.TP
+.B FSCONFIG_SET_FLAG
+Set the parameter named by
+.IR key
+to true.  This may incur error
+.B EINVAL
+if the parameter requires an argument.
+.TP
+.B FSCONFIG_SET_STRING
+Set the parameter named by
+.I key
+to a string.  This may incur error
+.B EINVAL
+if the parser doesn't want a parameter here, wants a non-string or the string
+cannot be interpreted appropriately.
+.I value
+points to a NUL-terminated string.
+.TP
+.B FSCONFIG_SET_BINARY
+Set the parameter named by
+.I key
+to be a binary blob argument.  This may cause
+.B EINVAL
+to be returned if the filesystem parser isn't expecting a binary blob and it
+can't be converted to something usable.
+.I value
+points to the data and
+.I aux
+indicates the size of the data.
+.TP
+.B FSCONFIG_SET_PATH
+Set the parameter named by
+.I key
+to the object at the provided path.
+.I value
+should point to a NULL-terminated pathname string and aux may indicate
+.B AT_FDCWD
+or a file descriptor indicating a directory from which to begin a relative
+pathwalk.  This may return any errors incurred by the pathwalk and may return
+.B EINVAL
+if the parameter isn't expecting a path.
+.IP
+Note that FSCONFIG_SET_STRING can be used instead, implying AT_FDCWD.
+.TP
+.B FSCONFIG_SET_PATH_EMPTY
+As FSCONFIG_SET_PATH, but with
+.B AT_EMPTY_PATH
+applied to the pathwalk.
+.TP
+.B FSCONFIG_SET_FD
+Set the parameter named by
+.I key
+to the file descriptor specified by
+.IR aux .
+This will incur
+.B EINVAL
+if the parameter doesn't expect a file descriptor or
+.B EBADF
+if the file descriptor is invalid.
+.IP
+Note that FSCONFIG_SET_STRING can be used instead with the file descriptor
+passed as a decimal string.
+.TP
+.B FSCONFIG_CMD_CREATE
+This command causes the filesystem to take the parameters set in the context
+and to try to create filesystem representation in the kernel.  If it can share
+an existing one, it may do that instead if the filesystem type and parameters
+permit that.  This is intended for use with
+.BR fsopen (2).
+.TP
+.B FSCONFIG_CMD_RECONFIGURE
+This command causes the filesystem to apply the parameters set in the context
+to an already existing filesystem representation in memory and to alter it.
+This is intended for use with
+.BR fspick (2),
+but may also by used against the context created by
+.BR fsopen()
+after
+.BR fsmount (2)
+has been called on it.
+
+.\"________________________________________________________
+.SH EXAMPLES
+.PP
+.in +4n
+.nf
+fsconfig(sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
+
+fsconfig(sfd, FSCONFIG_SET_STRING, "user_xattr", "false", 0);
+
+fsconfig(sfd, FSCONFIG_SET_BINARY, "ms_pac", pac_buffer, pac_size);
+
+fsconfig(sfd, FSCONFIG_SET_PATH, "journal", "/dev/sdd4", AT_FDCWD);
+
+dirfd = open("/dev/", O_PATH);
+fsconfig(sfd, FSCONFIG_SET_PATH, "journal", "sdd4", dirfd);
+
+fd = open("/overlays/mine/", O_PATH);
+fsconfig(sfd, FSCONFIG_SET_PATH_EMPTY, "lower_dir", "", fd);
+
+pipe(pipefds);
+fsconfig(sfd, FSCONFIG_SET_FD, "fd", NULL, pipefds[1]);
+.fi
+.in
+.PP
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, the function returns 0.  On error, \-1 is returned, and
+.I errno
+is set appropriately.
+.SH ERRORS
+The error values given below result from filesystem type independent
+errors.
+Each filesystem type may have its own special errors and its
+own special behavior.
+See the Linux kernel source code for details.
+.TP
+.B EACCES
+A component of a path was not searchable.
+(See also
+.BR path_resolution (7).)
+.TP
+.B EACCES
+Mounting a read-only filesystem was attempted without specifying the
+.RB ' ro '
+parameter.
+.TP
+.B EACCES
+A specified block device is located on a filesystem mounted with the
+.B MS_NODEV
+option.
+.\" mtk: Probably: write permission is required for MS_BIND, with
+.\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
+.TP
+.B EBADF
+The file descriptor given by
+.I fd
+or possibly by
+.I aux
+(depending on the command) is invalid.
+.TP
+.B EBUSY
+The context attached to
+.I fd
+is in the wrong state for the given command.
+.TP
+.B EBUSY
+The filesystem representation cannot be reconfigured read-only because it still
+holds files open for writing.
+.TP
+.B EFAULT
+One of the pointer arguments points outside the user address space.
+.TP
+.B EINVAL
+.I fd
+does not refer to a filesystem configuration context.
+.TP
+.B EINVAL
+One of the source parameters referred to an invalid superblock.
+.TP
+.B ELOOP
+Too many links encountered during pathname resolution.
+.TP
+.B ENAMETOOLONG
+A path name was longer than
+.BR MAXPATHLEN .
+.TP
+.B ENOENT
+A pathname was empty or had a nonexistent component.
+.TP
+.B ENOMEM
+The kernel could not allocate sufficient memory to complete the call.
+.TP
+.B ENOTBLK
+Once of the parameters does not refer to a block device (and a device was
+required).
+.TP
+.B ENOTDIR
+.IR pathname ,
+or a prefix of
+.IR source ,
+is not a directory.
+.TP
+.B EOPNOTSUPP
+The command given by
+.I cmd
+was not valid.
+.TP
+.B ENXIO
+The major number of a block device parameter is out of range.
+.TP
+.B EPERM
+The caller does not have the required privileges.
+.SH CONFORMING TO
+These functions are Linux-specific and should not be used in programs intended
+to be portable.
+.SH VERSIONS
+.BR fsconfig ()
+was added to Linux in kernel 5.2.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR fspick ()
+system call; call it using
+.BR syscall (2).
+.SH SEE ALSO
+.BR mountpoint (1),
+.BR fsmount (2),
+.BR fsopen (2),
+.BR fspick (2),
+.BR mount_namespaces (7),
+.BR path_resolution (7)
diff --git a/man2/fsmount.2 b/man2/fsmount.2
new file mode 100644
index 000000000..2bf59fc3e
--- /dev/null
+++ b/man2/fsmount.2
@@ -0,0 +1 @@
+.so man2/fsopen.2
diff --git a/man2/fsopen.2 b/man2/fsopen.2
new file mode 100644
index 000000000..6bed60cce
--- /dev/null
+++ b/man2/fsopen.2
@@ -0,0 +1,256 @@
+'\" t
+.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH FSOPEN 2 2019-10-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+fsopen, fsmount \- Filesystem parameterisation and mount creation
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/mount.h>
+.br
+.B #include <unistd.h>
+.br
+.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
+.br
+.BR "#include <sys/mount.h>       "
+.PP
+.BI "int fsopen(const char *" fsname ", unsigned int " flags );
+.PP
+.BI "int fsmount(int " fd ", unsigned int " flags ", unsigned int " mount_attrs );
+.fi
+.PP
+.IR Note :
+There are no glibc wrappers for these system calls.
+.SH DESCRIPTION
+.PP
+.BR fsopen ()
+creates a blank filesystem configuration context within the kernel for the
+filesystem named in the
+.I fsname
+parameter, puts it into creation mode and attaches it to a file descriptor,
+which it then returns.  The file descriptor can be marked close-on-exec by
+setting
+.B FSOPEN_CLOEXEC
+in
+.IR flags .
+.PP
+After calling fsopen(), the file descriptor should be passed to the
+.BR fsconfig (2)
+system call, using that to specify the desired filesystem and security
+parameters.
+.PP
+When the parameters are all set, the
+.BR fsconfig ()
+system call should then be called again with
+.B FSCONFIG_CMD_CREATE
+as the command argument to effect the creation.
+.RS
+.PP
+.BR "[!]\ NOTE" :
+Depending on the filesystem type and parameters, this may rather share an
+existing in-kernel filesystem representation instead of creating a new one.
+In such a case, the parameters specified may be discarded or may overwrite the
+parameters set by a previous mount - at the filesystem's discretion.
+.RE
+.PP
+The file descriptor also serves as a channel by which more comprehensive error,
+warning and information messages may be retrieved from the kernel using
+.BR read (2).
+
+.PP
+Once the creation command has been successfully run on a context, the context
+is switched into need-mount mode which prevents further configuration.  At
+this point,
+.BR fsmount ()
+should be called to create a mount object.
+.PP
+.BR fsmount ()
+takes the file descriptor returned by
+.BR fsopen ()
+and creates a mount object for the filesystem root specified there.  The
+attributes of the mount object are set from the
+.I mount_attrs
+parameter.  The attributes specify the propagation and mount restrictions to
+be applied to accesses through this mount.
+.PP
+The mount object is then attached to a new file descriptor that looks like one
+created by
+.BR open "(2) with " O_PATH " or " open_tree (2).
+This can be passed to
+.BR move_mount (2)
+to attach the mount object to a mountpoint, thereby completing the process.
+.PP
+The file descriptor returned by fsmount() is marked close-on-exec if
+FSMOUNT_CLOEXEC is specified in
+.IR flags .
+.PP
+After fsmount() has completed, the context created by fsopen() is reset and
+moved to reconfiguration state, allowing the new superblock to be
+reconfigured.  See
+.BR fspick (2)
+for details.
+.PP
+
+.\"________________________________________________________
+.SS Message Retrieval Interface
+The context file descriptor may be queried for message strings at any time by
+calling
+.BR read (2)
+on the file descriptor.  This will return formatted messages that are prefixed
+to indicate their class:
+.TP
+\fB"e <message>"\fP
+An error message string was logged.
+.TP
+\fB"i <message>"\fP
+An informational message string was logged.
+.TP
+\fB"w <message>"\fP
+An warning message string was logged.
+.PP
+Messages are removed from the queue as they're read.
+
+.\"________________________________________________________
+.SH EXAMPLES
+To illustrate the process, here's an example whereby this can be used to mount
+an ext4 filesystem on /dev/sdb1 onto /mnt.
+.PP
+.in +4n
+.nf
+sfd = fsopen("ext4", FSOPEN_CLOEXEC);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "source", "/dev/sdb1", 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "noatime", NULL, 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "acl", NULL, 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "user_attr", NULL, 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "iversion", NULL, 0);
+fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+mfd = fsmount(sfd, FSMOUNT_CLOEXEC, MS_RELATIME);
+move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
+.fi
+.in
+.PP
+Here, an ext4 context is created first and attached to sfd.  This is then told
+where its source will be, given a bunch of options and created.  Then
+fsmount() is called to create a mount object and
+.BR move_mount (2)
+is called to attach it to its intended mountpoint.
+.PP
+And here's an example of mounting from an NFS server and setting a Smack
+security module label on it too:
+.PP
+.in +4n
+.nf
+sfd = fsopen("nfs", 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "source", "example.com/pub/linux", 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "nfsvers", "3", 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "rsize", "65536", 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "wsize", "65536", 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "smackfsdef", "foolabel", 0);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "rdma", NULL, 0);
+fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+mfd = fsmount(sfd, 0, MS_NODEV);
+move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
+.fi
+.in
+.PP
+
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, both functions return a file descriptor.  On error, \-1 is
+returned, and
+.I errno
+is set appropriately.
+.SH ERRORS
+The error values given below result from filesystem type independent
+errors.
+Each filesystem type may have its own special errors and its
+own special behavior.
+See the Linux kernel source code for details.
+.TP
+.B EBUSY
+The context referred to by
+.I fd
+is not in the right state to be used by
+.BR fsmount ().
+.TP
+.B EFAULT
+One of the pointer arguments points outside the user address space.
+.TP
+.B EINVAL
+.I flags
+had an invalid flag set.
+.TP
+.B EINVAL
+.I mount_attrs,
+includes invalid
+.BR MOUNT_ATTR_*
+flags.
+.TP
+.B EMFILE
+The system has too many open files to create more.
+.TP
+.B ENFILE
+The process has too many open files to create more.
+.TP
+.B ENODEV
+Filesystem
+.I fsname
+not configured in the kernel.
+.TP
+.B ENOMEM
+The kernel could not allocate sufficient memory to complete the call.
+.TP
+.B EPERM
+The caller does not have the required privileges.
+.SH CONFORMING TO
+These functions are Linux-specific and should not be used in programs intended
+to be portable.
+.SH VERSIONS
+.BR fsopen "(), and " fsmount ()
+were added to Linux in kernel 5.2.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR fsopen "() or " fsmount "()"
+system calls; call them using
+.BR syscall (2).
+.SH SEE ALSO
+.BR mountpoint (1),
+.BR fsconfig (2),
+.BR fspick (2),
+.BR move_mount (2),
+.BR open_tree (2),
+.BR umount (2),
+.BR mount_namespaces (7),
+.BR path_resolution (7),
+.BR findmnt (8),
+.BR lsblk (8),
+.BR mount (8),
+.BR umount (8)
diff --git a/man2/fspick.2 b/man2/fspick.2
new file mode 100644
index 000000000..02f0ccf48
--- /dev/null
+++ b/man2/fspick.2
@@ -0,0 +1,195 @@
+'\" t
+.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH FSPICK 2 2019-10-10 "Linux" "Linux Programmer's Manual"
+.SH NAME
+fspick \- Select filesystem for reconfiguration
+.SH SYNOPSIS
+.nf
+.B #include <sys/types.h>
+.br
+.B #include <sys/mount.h>
+.br
+.B #include <unistd.h>
+.br
+.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
+.PP
+.BI "int fspick(int " dirfd ", const char *" pathname ", unsigned int " flags );
+.fi
+.PP
+.IR Note :
+There is no glibc wrapper for this system call.
+.SH DESCRIPTION
+.PP
+.BR fspick ()
+creates a new filesystem configuration context within the kernel and attaches a
+pre-existing superblock to it so that it can be reconfigured (similar to
+.BR mount (8)
+with the "-o remount" option).  The configuration context is marked as being in
+reconfiguration mode and attached to a file descriptor, which is returned to
+the caller.  This can be marked close-on-exec by setting
+.B FSPICK_CLOEXEC
+in
+.IR flags .
+.PP
+The target is whichever superblock backs the object determined by
+.IR dfd ", " pathname " and " flags .
+The following can be set in
+.I flags
+to control the pathwalk to that object:
+.TP
+.B FSPICK_SYMLINK_NOFOLLOW
+Don't follow symbolic links in the terminal component of the path.
+.TP
+.B FSPICK_NO_AUTOMOUNT
+Don't follow automounts in the terminal component of the path.
+.TP
+.B FSPICK_EMPTY_PATH
+Allow an empty string to be specified as the pathname.  This allows
+.I dirfd
+to specify a path exactly.
+.PP
+After calling fspick(), the file descriptor should be passed to the
+.BR fsconfig (2)
+system call, using that to specify the desired changes to filesystem and
+security parameters.
+.PP
+When the parameters are all set, the
+.BR fsconfig ()
+system call should then be called again with
+.B FSCONFIG_CMD_RECONFIGURE
+as the command argument to effect the reconfiguration.
+.PP
+After the reconfiguration has taken place, the context is wiped clean (apart
+from the superblock attachment, which remains) and can be reused to make
+another reconfiguration.
+.PP
+The file descriptor also serves as a channel by which more comprehensive error,
+warning and information messages may be retrieved from the kernel using
+.BR read (2).
+
+
+.\"________________________________________________________
+.SS Message Retrieval Interface
+The context file descriptor may be queried for message strings at any time by
+calling
+.BR read (2)
+on the file descriptor.  This will return formatted messages that are prefixed
+to indicate their class:
+.TP
+\fB"e <message>"\fP
+An error message string was logged.
+.TP
+\fB"i <message>"\fP
+An informational message string was logged.
+.TP
+\fB"w <message>"\fP
+An warning message string was logged.
+.PP
+Messages are removed from the queue as they're read and the queue has a limited
+depth, so it's possible for some to get lost.
+
+.\"________________________________________________________
+.SH EXAMPLES
+To illustrate the process, here's an example whereby this can be used to
+reconfigure a filesystem:
+.PP
+.in +4n
+.nf
+sfd = fspick(AT_FDCWD, "/mnt", FSPICK_NO_AUTOMOUNT | FSPICK_CLOEXEC);
+fsconfig(sfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
+fsconfig(sfd, FSCONFIG_SET_STRING, "user_xattr", "false", 0);
+fsconfig(sfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0);
+.fi
+.in
+.PP
+
+
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+.SH RETURN VALUE
+On success, the function returns a file descriptor.  On error, \-1 is returned,
+and
+.I errno
+is set appropriately.
+.SH ERRORS
+The error values given below result from filesystem type independent
+errors.
+Each filesystem type may have its own special errors and its
+own special behavior.
+See the Linux kernel source code for details.
+.TP
+.B EACCES
+A component of a path was not searchable.
+(See also
+.BR path_resolution (7).)
+.TP
+.B EFAULT
+.I pathname
+points outside the user address space.
+.TP
+.B EINVAL
+.I flags
+includes an undefined value.
+.TP
+.B ELOOP
+Too many links encountered during pathname resolution.
+.TP
+.B EMFILE
+The system has too many open files to create more.
+.TP
+.B ENFILE
+The process has too many open files to create more.
+.TP
+.B ENAMETOOLONG
+A pathname was longer than
+.BR MAXPATHLEN .
+.TP
+.B ENOENT
+A pathname was empty or had a nonexistent component.
+.TP
+.B ENOMEM
+The kernel could not allocate sufficient memory to complete the call.
+.TP
+.B EPERM
+The caller does not have the required privileges.
+.SH CONFORMING TO
+These functions are Linux-specific and should not be used in programs intended
+to be portable.
+.SH VERSIONS
+.BR fsopen "(), " fsmount "() and " fspick ()
+were added to Linux in kernel 5.2.
+.SH NOTES
+Glibc does not (yet) provide a wrapper for the
+.BR fspick "()"
+system call; call it using
+.BR syscall (2).
+.SH SEE ALSO
+.BR mountpoint (1),
+.BR fsconfig (2),
+.BR fsopen (2),
+.BR path_resolution (7),
+.BR mount (8)
-- 
2.24.1


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2)
  2020-02-07 17:42 ` [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2) Petr Vorel
@ 2020-02-26 11:48   ` Petr Vorel
  0 siblings, 0 replies; 4+ messages in thread
From: Petr Vorel @ 2020-02-26 11:48 UTC (permalink / raw)
  To: Michael Kerrisk
  Cc: David Howells, Zorro Lang, linux-fsdevel, linux-kernel, linux-man

Hi,

gentle ping. Could these 2 patches be merged?

Kind regards,
Petr

> From: David Howells <dhowells@redhat.com>

> Add manual pages to document the move_mount and open_tree() system calls.

> Reviewed-by: Petr Vorel <pvorel@suse.cz>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Petr Vorel <pvorel@suse.cz>
> ---
> Hi,

> * man2/move_mount.2
> fixed MOVE_MOUNT_F_NO_AUTOMOUNT => MOVE_MOUNT_F_AUTOMOUNTS
> and MOVE_MOUNT_T_NO_AUTOMOUNT => MOVE_MOUNT_T_AUTOMOUNTS
> maybe mention -EPERM on !may_mount() ?

> * man2/open_tree.2
> maybe mention -EPERM on (detached && !may_mount()) ?

> Kind regards,
> Petr

>  man2/move_mount.2 | 271 ++++++++++++++++++++++++++++++++++++++++++++++
>  man2/open_tree.2  | 260 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 531 insertions(+)
>  create mode 100644 man2/move_mount.2
>  create mode 100644 man2/open_tree.2

> diff --git a/man2/move_mount.2 b/man2/move_mount.2
> new file mode 100644
> index 000000000..bca352ad3
> --- /dev/null
> +++ b/man2/move_mount.2
> @@ -0,0 +1,271 @@
> +'\" t
> +.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" Permission is granted to make and distribute verbatim copies of this
> +.\" manual provided the copyright notice and this permission notice are
> +.\" preserved on all copies.
> +.\"
> +.\" Permission is granted to copy and distribute modified versions of this
> +.\" manual under the conditions for verbatim copying, provided that the
> +.\" entire resulting derived work is distributed under the terms of a
> +.\" permission notice identical to this one.
> +.\"
> +.\" Since the Linux kernel and libraries are constantly changing, this
> +.\" manual page may be incorrect or out-of-date.  The author(s) assume no
> +.\" responsibility for errors or omissions, or for damages resulting from
> +.\" the use of the information contained herein.  The author(s) may not
> +.\" have taken the same level of care in the production of this manual,
> +.\" which is licensed free of charge, as they might when working
> +.\" professionally.
> +.\"
> +.\" Formatted or processed versions of this manual, if unaccompanied by
> +.\" the source, must acknowledge the copyright and authors of this work.
> +.\" %%%LICENSE_END
> +.\"
> +.TH MOVE_MOUNT 2 2019-10-10 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +move_mount \- Move mount objects around the filesystem topology
> +.SH SYNOPSIS
> +.nf
> +.B #include <sys/types.h>
> +.br
> +.B #include <sys/mount.h>
> +.br
> +.B #include <unistd.h>
> +.br
> +.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
> +.PP
> +.BI "int move_mount(int " from_dirfd ", const char *" from_pathname ","
> +.BI "               int " to_dirfd ", const char *" to_pathname ","
> +.BI "               unsigned int " flags );
> +.fi
> +.PP
> +.IR Note :
> +There is no glibc wrapper for this system call.
> +.SH DESCRIPTION
> +The
> +.BR move_mount ()
> +call moves a mount from one place to another; it can also be used to attach an
> +unattached mount created by
> +.BR fsmount "() or " open_tree "() with " OPEN_TREE_CLONE .
> +.PP
> +If
> +.BR move_mount ()
> +is called repeatedly with a file descriptor that refers to a mount object,
> +then the object will be attached/moved the first time and then moved again and
> +again and again, detaching it from the previous mountpoint each time.
> +.PP
> +To access the source mount object or the destination mountpoint, no
> +permissions are required on the object itself, but if either pathname is
> +supplied, execute (search) permission is required on all of the directories
> +specified in
> +.IR from_pathname " or " to_pathname .
> +.PP
> +The caller does, however, require the appropriate capabilities or permission
> +to effect a mount.
> +.PP
> +.BR move_mount ()
> +uses
> +.IR from_pathname ", " from_dirfd " and part of " flags
> +to locate the mount object to be moved and
> +.IR to_pathname ", " to_dirfd " and another part of " flags
> +to locate the destination mountpoint.  Each lookup can be done in one of a
> +variety of ways:
> +.TP
> +[*] By absolute path.
> +The pathname points to an absolute path and the dirfd is ignored.  The file is
> +looked up by name, starting from the root of the filesystem as seen by the
> +calling process.
> +.TP
> +[*] By cwd-relative path.
> +The pathname points to a relative path and the dirfd is
> +.IR AT_FDCWD .
> +The file is looked up by name, starting from the current working directory.
> +.TP
> +[*] By dir-relative path.
> +The pathname points to relative path and the dirfd indicates a file descriptor
> +pointing to a directory.  The file is looked up by name, starting from the
> +directory specified by
> +.IR dirfd .
> +.TP
> +[*] By file descriptor.
> +The pathname points to "", the dirfd points directly to the mount object to
> +move or the destination mount point and the appropriate
> +.B *_EMPTY_PATH
> +flag is set.
> +.PP
> +.I flags
> +can be used to influence a path-based lookup.  A value for
> +.I flags
> +is constructed by OR'ing together zero or more of the following constants:
> +.TP
> +.BR MOVE_MOUNT_F_EMPTY_PATH
> +.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
> +If
> +.I from_pathname
> +is an empty string, operate on the file referred to by
> +.IR from_dirfd
> +(which may have been obtained using the
> +.BR open (2)
> +.B O_PATH
> +flag or
> +.BR open_tree ()).
> +If
> +.I from_dirfd
> +is
> +.BR AT_FDCWD ,
> +the call operates on the current working directory.
> +In this case,
> +.I from_dirfd
> +can refer to any type of file, not just a directory.
> +This flag is Linux-specific; define
> +.B _GNU_SOURCE
> +.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
> +to obtain its definition.
> +.TP
> +.B MOVE_MOUNT_T_EMPTY_PATH
> +As above, but operating on
> +.IR to_pathname " and " to_dirfd .
> +.TP
> +.B MOVE_MOUNT_F_AUTOMOUNTS
> +Don't automount the terminal ("basename") component of
> +.I from_pathname
> +if it is a directory that is an automount point.  This allows a mount object
> +that has an automount point at its root to be moved and prevents unintended
> +triggering of an automount point.
> +The
> +.B MOVE_MOUNT_F_AUTOMOUNTS
> +flag has no effect if the automount point has already been mounted over.
> +.TP
> +.B MOVE_MOUNT_T_AUTOMOUNTS
> +As above, but operating on
> +.IR to_pathname " and " to_dirfd .
> +This allows an automount point to be manually mounted over.
> +.TP
> +.B MOVE_MOUNT_F_SYMLINKS
> +If
> +.I from_pathname
> +is a symbolic link, then dereference it.  The default for
> +.BR move_mount ()
> +is to not follow symlinks.
> +.TP
> +.B MOVE_MOUNT_T_SYMLINKS
> +As above, but operating on
> +.IR to_pathname " and " to_dirfd .
> +
> +.SH EXAMPLES
> +The
> +.BR move_mount ()
> +function can be used like the following:
> +.PP
> +.RS
> +.nf
> +move_mount(AT_FDCWD, "/a", AT_FDCWD, "/b", 0);
> +.fi
> +.RE
> +.PP
> +This would move the object mounted on "/a" to "/b".  It can also be used in
> +conjunction with
> +.BR open_tree "(2) or " open "(2) with " O_PATH :
> +.PP
> +.RS
> +.nf
> +fd = open_tree(AT_FDCWD, "/mnt", 0);
> +move_mount(fd, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
> +move_mount(fd, "", AT_FDCWD, "/mnt3", MOVE_MOUNT_F_EMPTY_PATH);
> +move_mount(fd, "", AT_FDCWD, "/mnt4", MOVE_MOUNT_F_EMPTY_PATH);
> +.fi
> +.RE
> +.PP
> +This would attach the path point for "/mnt" to fd, then it would move the
> +mount to "/mnt2", then move it to "/mnt3" and finally to "/mnt4".
> +.PP
> +It can also be used to attach new mounts:
> +.PP
> +.RS
> +.nf
> +sfd = fsopen("ext4", FSOPEN_CLOEXEC);
> +fsconfig(sfd, FSCONFIG_SET_STRING, "source", "/dev/sda1", 0);
> +fsconfig(sfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
> +fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
> +mfd = fsmount(sfd, FSMOUNT_CLOEXEC, MOUNT_ATTR_NODEV);
> +move_mount(mfd, "", AT_FDCWD, "/home", MOVE_MOUNT_F_EMPTY_PATH);
> +.fi
> +.RE
> +.PP
> +Which would open the Ext4 filesystem mounted on "/dev/sda1", turn on user
> +extended attribute support and create a mount object for it.  Finally, the new
> +mount object would be attached with
> +.BR move_mount ()
> +to "/home".
> +
> +
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.SH RETURN VALUE
> +On success, 0 is returned.  On error, \-1 is returned, and
> +.I errno
> +is set appropriately.
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Search permission is denied for one of the directories
> +in the path prefix of
> +.IR pathname .
> +(See also
> +.BR path_resolution (7).)
> +.TP
> +.B EBADF
> +.IR from_dirfd " or " to_dirfd
> +is not a valid open file descriptor.
> +.TP
> +.B EFAULT
> +.IR from_pathname " or " to_pathname
> +is NULL or either one point to a location outside the process's accessible
> +address space.
> +.TP
> +.B EINVAL
> +Reserved flag specified in
> +.IR flags .
> +.TP
> +.B ELOOP
> +Too many symbolic links encountered while traversing the pathname.
> +.TP
> +.B ENAMETOOLONG
> +.IR from_pathname " or " to_pathname
> +is too long.
> +.TP
> +.B ENOENT
> +A component of
> +.IR from_pathname " or " to_pathname
> +does not exist, or one is an empty string and the appropriate
> +.B *_EMPTY_PATH
> +was not specified in
> +.IR flags .
> +.TP
> +.B ENOMEM
> +Out of memory (i.e., kernel memory).
> +.TP
> +.B ENOTDIR
> +A component of the path prefix of
> +.IR from_pathname " or " to_pathname
> +is not a directory or one or the other is relative and the appropriate
> +.I *_dirfd
> +is a file descriptor referring to a file other than a directory.
> +.SH VERSIONS
> +.BR move_mount ()
> +was added to Linux in kernel 5.2.
> +.SH CONFORMING TO
> +.BR move_mount ()
> +is Linux-specific.
> +.SH NOTES
> +Glibc does not (yet) provide a wrapper for the
> +.BR move_mount ()
> +system call; call it using
> +.BR syscall (2).
> +.SH SEE ALSO
> +.BR fsmount (2),
> +.BR fsopen (2),
> +.BR open_tree (2)
> diff --git a/man2/open_tree.2 b/man2/open_tree.2
> new file mode 100644
> index 000000000..56783898f
> --- /dev/null
> +++ b/man2/open_tree.2
> @@ -0,0 +1,260 @@
> +'\" t
> +.\" Copyright (c) 2019 David Howells <dhowells@redhat.com>
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" Permission is granted to make and distribute verbatim copies of this
> +.\" manual provided the copyright notice and this permission notice are
> +.\" preserved on all copies.
> +.\"
> +.\" Permission is granted to copy and distribute modified versions of this
> +.\" manual under the conditions for verbatim copying, provided that the
> +.\" entire resulting derived work is distributed under the terms of a
> +.\" permission notice identical to this one.
> +.\"
> +.\" Since the Linux kernel and libraries are constantly changing, this
> +.\" manual page may be incorrect or out-of-date.  The author(s) assume no
> +.\" responsibility for errors or omissions, or for damages resulting from
> +.\" the use of the information contained herein.  The author(s) may not
> +.\" have taken the same level of care in the production of this manual,
> +.\" which is licensed free of charge, as they might when working
> +.\" professionally.
> +.\"
> +.\" Formatted or processed versions of this manual, if unaccompanied by
> +.\" the source, must acknowledge the copyright and authors of this work.
> +.\" %%%LICENSE_END
> +.\"
> +.TH OPEN_TREE 2 2019-10-10 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +open_tree \- Pick or clone mount object and attach to fd
> +.SH SYNOPSIS
> +.nf
> +.B #include <sys/types.h>
> +.br
> +.B #include <sys/mount.h>
> +.br
> +.B #include <unistd.h>
> +.br
> +.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
> +.PP
> +.BI "int open_tree(int " dirfd ", const char *" pathname ", unsigned int " flags );
> +.fi
> +.PP
> +.IR Note :
> +There are no glibc wrappers for these system calls.
> +.SH DESCRIPTION
> +.BR open_tree ()
> +picks the mount object specified by the pathname and attaches it to a new file
> +descriptor or clones it and attaches the clone to the file descriptor.  The
> +resultant file descriptor is indistinguishable from one produced by
> +.BR open "(2) with " O_PATH .
> +.PP
> +In the case that the mount object is cloned, the clone will be "unmounted" and
> +destroyed when the file descriptor is closed if it is not otherwise mounted
> +somewhere by calling
> +.BR move_mount (2).
> +.PP
> +To select a mount object, no permissions are required on the object referred
> +to by the path, but execute (search) permission is required on all of the
> +directories in
> +.I pathname
> +that lead to the object.
> +.PP
> +To clone an object, however, the caller must have mount capabilities and
> +permissions.
> +.PP
> +.BR open_tree ()
> +uses
> +.IR pathname ", " dirfd " and " flags
> +to locate the target object in one of a variety of ways:
> +.TP
> +[*] By absolute path.
> +.I pathname
> +points to an absolute path and
> +.I dirfd
> +is ignored.  The object is looked up by name, starting from the root of the
> +filesystem as seen by the calling process.
> +.TP
> +[*] By cwd-relative path.
> +.I pathname
> +points to a relative path and
> +.IR dirfd " is " AT_FDCWD .
> +The object is looked up by name, starting from the current working directory.
> +.TP
> +[*] By dir-relative path.
> +.I pathname
> +points to relative path and
> +.I dirfd
> +indicates a file descriptor pointing to a directory.  The object is looked up
> +by name, starting from the directory specified by
> +.IR dirfd .
> +.TP
> +[*] By file descriptor.
> +.I pathname
> +is "",
> +.I dirfd
> +indicates a file descriptor and
> +.B AT_EMPTY_PATH
> +is set in
> +.IR flags .
> +The mount attached to the file descriptor is queried directly.  The file
> +descriptor may point to any type of file, not just a directory.
> +
> +.\"______________________________________________________________
> +.PP
> +.I flags
> +can be used to control the operation of the function and to influence a
> +path-based lookup.  A value for
> +.I flags
> +is constructed by OR'ing together zero or more of the following constants:
> +.TP
> +.BR AT_EMPTY_PATH
> +.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
> +If
> +.I pathname
> +is an empty string, operate on the file referred to by
> +.IR dirfd
> +(which may have been obtained from
> +.BR open "(2) with"
> +.BR O_PATH ", from " fsmount (2)
> +or from another
> +.BR open_tree ()).
> +If
> +.I dirfd
> +is
> +.BR AT_FDCWD ,
> +the call operates on the current working directory.
> +In this case,
> +.I dirfd
> +can refer to any type of file, not just a directory.
> +This flag is Linux-specific; define
> +.B _GNU_SOURCE
> +.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
> +to obtain its definition.
> +.TP
> +.BR AT_NO_AUTOMOUNT
> +Don't automount the terminal ("basename") component of
> +.I pathname
> +if it is a directory that is an automount point.  This flag allows the
> +automount point itself to be picked up or a mount cloned that is rooted on the
> +automount point.  The
> +.B AT_NO_AUTOMOUNT
> +flag has no effect if the mount point has already been mounted over.
> +This flag is Linux-specific; define
> +.B _GNU_SOURCE
> +.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
> +to obtain its definition.
> +.TP
> +.B AT_SYMLINK_NOFOLLOW
> +If
> +.I pathname
> +is a symbolic link, do not dereference it: instead pick up or clone a mount
> +rooted on the link itself.
> +.TP
> +.B OPEN_TREE_CLOEXEC
> +Set the close-on-exec flag for the new file descriptor.  This will cause the
> +file descriptor to be closed automatically when a process exec's.
> +.TP
> +.B OPEN_TREE_CLONE
> +Rather than directly attaching the selected object to the file descriptor,
> +clone the object, set the root of the new mount object to that point and
> +attach the clone to the file descriptor.
> +.TP
> +.B AT_RECURSIVE
> +This is only permitted in conjunction with OPEN_TREE_CLONE.  It causes the
> +entire mount subtree rooted at the selected spot to be cloned rather than just
> +that one mount object.
> +
> +
> +.SH EXAMPLE
> +The
> +.BR open_tree ()
> +function can be used like the following:
> +.PP
> +.RS
> +.nf
> +fd1 = open_tree(AT_FDCWD, "/mnt", 0);
> +fd2 = open_tree(fd1, "",
> +                AT_EMPTY_PATH | OPEN_TREE_CLONE | AT_RECURSIVE);
> +move_mount(fd2, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
> +.fi
> +.RE
> +.PP
> +This would attach the path point for "/mnt" to fd1, then it would copy the
> +entire subtree at the point referred to by fd1 and attach that to fd2; lastly,
> +it would attach the clone to "/mnt2".
> +
> +
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
> +.SH RETURN VALUE
> +On success, the new file descriptor is returned.  On error, \-1 is returned,
> +and
> +.I errno
> +is set appropriately.
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Search permission is denied for one of the directories
> +in the path prefix of
> +.IR pathname .
> +(See also
> +.BR path_resolution (7).)
> +.TP
> +.B EBADF
> +.I dirfd
> +is not a valid open file descriptor.
> +.TP
> +.B EFAULT
> +.I pathname
> +is NULL or
> +.IR pathname
> +point to a location outside the process's accessible address space.
> +.TP
> +.B EINVAL
> +Reserved flag specified in
> +.IR flags .
> +.TP
> +.B ELOOP
> +Too many symbolic links encountered while traversing the pathname.
> +.TP
> +.B ENAMETOOLONG
> +.I pathname
> +is too long.
> +.TP
> +.B ENOENT
> +A component of
> +.I pathname
> +does not exist, or
> +.I pathname
> +is an empty string and
> +.B AT_EMPTY_PATH
> +was not specified in
> +.IR flags .
> +.TP
> +.B ENOMEM
> +Out of memory (i.e., kernel memory).
> +.TP
> +.B ENOTDIR
> +A component of the path prefix of
> +.I pathname
> +is not a directory or
> +.I pathname
> +is relative and
> +.I dirfd
> +is a file descriptor referring to a file other than a directory.
> +.SH VERSIONS
> +.BR open_tree ()
> +was added to Linux in kernel 5.2.
> +.SH CONFORMING TO
> +.BR open_tree ()
> +is Linux-specific.
> +.SH NOTES
> +Glibc does not (yet) provide a wrapper for the
> +.BR open_tree ()
> +system call; call it using
> +.BR syscall (2).
> +.SH SEE ALSO
> +.BR fsmount (2),
> +.BR move_mount (2),
> +.BR open (2)

^ permalink raw reply	[flat|nested] 4+ messages in thread

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Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-07 17:42 [PATCH v2 0/2] New mount API syscalls Petr Vorel
2020-02-07 17:42 ` [PATCH v2 1/2] Add manpages for move_mount(2) and open_tree(2) Petr Vorel
2020-02-26 11:48   ` Petr Vorel
2020-02-07 17:42 ` [PATCH v2 2/2] Add manpage for fsopen(2), fspick(2) and fsmount(2) Petr Vorel

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