This is a new API added in Linux 6.15, and is effectively just a minor expansion of open_tree(2) in order to allow for MOUNT_ATTR_IDMAP to be changed for an existing ID-mapped mount. Glibc does not yet have a wrapper for this. Cc: Christian Brauner <brauner@xxxxxxxxxx> Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx> --- man/man2/open_tree.2 | 74 +++++++++++++++++++++++++++++++++++++++++++++++ man/man2/open_tree_attr.2 | 1 + 2 files changed, 75 insertions(+) diff --git a/man/man2/open_tree.2 b/man/man2/open_tree.2 index 3d38e27b5254..6e7ec4998d42 100644 --- a/man/man2/open_tree.2 +++ b/man/man2/open_tree.2 @@ -15,7 +15,19 @@ .SH SYNOPSIS .BR "#include <sys/mount.h>" .P .BI "int open_tree(int " dirfd ", const char *" path ", unsigned int " flags ");" +.P +.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */" +.P +.BI "int syscall(SYS_open_tree_attr, int " dirfd ", const char *" path "," +.BI " unsigned int " flags ", struct mount_attr *" attr ", \ +size_t " size ");" .fi +.P +.IR Note : +glibc provides no wrapper for +.BR open_tree_attr (), +necessitating the use of +.BR syscall (2). .SH DESCRIPTION The .BR open_tree () @@ -222,6 +234,64 @@ .SH DESCRIPTION and attach it to the file descriptor. This flag is only permitted in conjunction with .BR \%OPEN_TREE_CLONE . +.SS open_tree_attr() +The +.BR open_tree_attr () +system call operates in exactly the same way as +.BR open_tree (), +except for the differences described here. +.P +After performing the same operation as with +.BR open_tree (), +(before returning the resulting file descriptor) +.BR open_tree_attr () +will apply the mount attributes requested in +.I attr +to the mount object. +(See +.BR mount_attr (2type) +for a description of the +.I mount_attr +structure. +As described in +.BR mount_setattr (2), +.I size +must be set to +.I sizeof(struct mount_attr) +in order to support future extensions.) +.P +For the most part, the application of +.I attr +has identical semantics to +.BR mount_setattr (2), +except that it is possible to change the +.B \%MOUNT_ATTR_IDMAP +attribute for a mount object +that is already configured as an ID-mapped mount. +This is usually forbidden by +.BR mount_setattr (2) +and thus +.BR open_tree_attr () +is currently the only permitted mechanism to change this attribute. +Changing an ID-mapped mount is only permitted +if a new detached mount object is being created with +.I flags +including +.BR \%OPEN_TREE_CLONE . +.P +If +.I flags +contains +.BR \%AT_RECURSIVE , +then the attributes are applied recursively +(just as when +.BR mount_setattr (2) +is called with +.BR \%AT_RECURSIVE ). +This applies in addition to the +.BR open_tree ()-specific +behaviour regarding +.BR \%AT_RECURSIVE . .SH RETURN VALUE On success, a new file descriptor is returned. On error, \-1 is returned, and @@ -316,9 +386,13 @@ .SH ERRORS .SH STANDARDS Linux. .SH HISTORY +.SS open_tree() Linux 5.2. .\" commit a07b20004793d8926f78d63eb5980559f7813404 glibc 2.36. +.SS open_tree_attr() +Linux 6.15. +.\" commit c4a16820d90199409c9bf01c4f794e1e9e8d8fd8 .SH NOTES .SS Anonymous mount namespaces The bind-mount mount objects created by diff --git a/man/man2/open_tree_attr.2 b/man/man2/open_tree_attr.2 new file mode 100644 index 000000000000..e57269bbd269 --- /dev/null +++ b/man/man2/open_tree_attr.2 @@ -0,0 +1 @@ +.so man2/open_tree.2 -- 2.50.1
