Support idmapped mount in user namespace

Linux 5.17 commit torvalds/linux@5dfbfe71e enables "the idmapping 
infrastructure to support idmapped mounts of filesystems mounted 
with an idmapping". Update the OpenZFS accordingly to improve the 
idmapped mount support. 

This pull request contains the following changes:

- xattr setter functions are fixed to take mnt_ns argument. Without
  this, cp -p would fail for an idmapped mount in a user namespace.
- idmap_util is enhanced/fixed for its use in a user ns context.
- One test case added to test idmapped mount in a user ns.

Reviewed-by: Christian Brauner <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Youzhong Yang <[email protected]>
Closes #14097

1 files changed, 24 insertions, 0 deletions

diff --git a/config/kernel-iattr-vfsid.m4 b/config/kernel-iattr-vfsid.m4
new file mode 100644
index 000000000..75bc4613b
--- /dev/null
+++ b/config/kernel-iattr-vfsid.m4
@@ -0,0 +1,24 @@
+dnl #
+dnl # 6.0 API change
+dnl # struct iattr has two unions for the uid and gid
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_IATTR_VFSID], [
+	ZFS_LINUX_TEST_SRC([iattr_vfsid], [
+		#include <linux/fs.h>
+	], [
+		struct iattr ia;
+		ia.ia_vfsuid = (vfsuid_t){0};
+		ia.ia_vfsgid = (vfsgid_t){0};
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_IATTR_VFSID], [
+	AC_MSG_CHECKING([whether iattr->ia_vfsuid and iattr->ia_vfsgid exist])
+	ZFS_LINUX_TEST_RESULT([iattr_vfsid], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_IATTR_VFSID, 1,
+		    [iattr->ia_vfsuid and iattr->ia_vfsgid exist])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])