| Message ID | 20200207174236.18882-2-pvorel@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | New mount API syscalls | expand |
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 +.\" manual page may be incorrect or out-of-date.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)
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)