fs: port mnt_idmap() and file_mnt_idmap() to const mnt_idmap

Now that everything takes a mnt_idmap as const store a const pointer in
struct vfsmount, struct mount_kattr and struct kstatmount and return one
from mnt_idmap(), file_mnt_idmap() and ovl_upper_mnt_idmap(). Finally,
also make mnt_idmap_get() return a const pointer. Also convert the
remaining local variables that are initialized from the accessors.

alloc_mnt_idmap() keeps returning a non-const pointer. It is the only
place where an idmapping is actually written to.

Link: https://patch.msgid.link/20260901-work-idmap-const-v1-26-54ccd48e100b@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Seth Forshee <sforshee@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Documentation/filesystems/porting.rst

@@ -1409,3 +1409,16 @@ use only if you have no alternative.
 The .create inode_operation no longer receives the 'excl' arg.  It must
 always assume the file does not already exist.  If the filesystem needs
 to be involved in non-exclusive create, it should provide atomic_open.
+
+---
+
+**mandatory**
+
+All struct mnt_idmap pointers handed to filesystems are const now.
+->create(), ->mkdir(), ->mknod(), ->symlink(), ->rename(), ->setattr(),
+->getattr(), ->permission(), ->tmpfile(), ->get_acl(), ->set_acl() and
+->fileattr_set() as well as the xattr ->set() handler and the vfs_*()
+helpers take a const struct mnt_idmap *. mnt_idmap() and file_mnt_idmap()
+return one. The idmapping is immutable so nothing should have modified it
+anyway. References are taken and dropped via mnt_idmap_get() and
+mnt_idmap_put() as before, both accept a const pointer.

fs/backing-file.c

@@ -59,7 +59,7 @@ struct file *backing_tmpfile_open(const struct file *user_file, int flags,
 				  const struct path *real_parentpath,
 				  umode_t mode, const struct cred *cred)
 {
-	struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt);
+	const struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt);
 	const struct path *user_path = &user_file->f_path;
 	struct file *f;
 	int error;

fs/btrfs/ioctl.c

@@ -1149,7 +1149,7 @@ static noinline int __btrfs_ioctl_snap_create(struct file *file,
 {
 	int ret;
 	struct qstr qname = QSTR(name);
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 
 	if (!S_ISDIR(file_inode(file)->i_mode))
 		return -ENOTDIR;
@@ -2226,7 +2226,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	struct btrfs_root *dest = NULL;
 	struct btrfs_ioctl_vol_args AUTO_KFREE(vol_args);
 	struct btrfs_ioctl_vol_args_v2 AUTO_KFREE(vol_args2);
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	char *subvol_name, *subvol_name_ptr = NULL;
 	int ret = 0;
 	bool destroy_parent = false;

fs/ceph/file.c

@@ -795,7 +795,7 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 		     struct file *file, unsigned flags, umode_t mode)
 {
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct ceph_fs_client *fsc = ceph_sb_to_fs_client(dir->i_sb);
 	struct ceph_client *cl = fsc->client;
 	struct ceph_mds_client *mdsc = fsc->mdsc;

fs/coredump.c

@@ -878,7 +878,7 @@ static inline bool coredump_force_suid_safe(const struct coredump_params *cprm)
 static bool coredump_file(struct core_name *cn, struct coredump_params *cprm,
 			  const struct linux_binfmt *binfmt)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct inode *inode;
 	struct file *file __free(fput) = NULL;
 	int open_flags = O_CREAT | O_WRONLY | O_NOFOLLOW | O_LARGEFILE | O_EXCL;

fs/exec.c

@@ -1339,7 +1339,7 @@ EXPORT_SYMBOL(begin_new_exec);
 void would_dump(struct linux_binprm *bprm, struct file *file)
 {
 	struct inode *inode = file_inode(file);
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	if (inode_permission(idmap, inode, MAY_READ) < 0) {
 		struct user_namespace *old, *user_ns;
 		bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
@@ -1623,7 +1623,7 @@ static void check_unsafe_exec(struct linux_binprm *bprm)
 static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file)
 {
 	/* Handle suid and sgid on files */
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct inode *inode = file_inode(file);
 	unsigned int mode;
 	vfsuid_t vfsuid;

fs/ext4/ioctl.c

@@ -1539,7 +1539,7 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
 	struct super_block *sb = inode->i_sb;
-	struct mnt_idmap *idmap = file_mnt_idmap(filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(filp);
 
 	ext4_debug("cmd = %u, arg = %lu\n", cmd, arg);
 

fs/f2fs/file.c

@@ -2361,7 +2361,7 @@ static int f2fs_ioc_getversion(struct file *filp, unsigned long arg)
 static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 {
 	struct inode *inode = file_inode(filp);
-	struct mnt_idmap *idmap = file_mnt_idmap(filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	struct f2fs_inode_info *fi = F2FS_I(inode);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	loff_t isize;
@@ -2473,7 +2473,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 static int f2fs_ioc_commit_atomic_write(struct file *filp)
 {
 	struct inode *inode = file_inode(filp);
-	struct mnt_idmap *idmap = file_mnt_idmap(filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	int ret;
 
 	if (!(filp->f_mode & FMODE_WRITE))
@@ -2508,7 +2508,7 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
 static int f2fs_ioc_abort_atomic_write(struct file *filp)
 {
 	struct inode *inode = file_inode(filp);
-	struct mnt_idmap *idmap = file_mnt_idmap(filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(filp);
 	int ret;
 
 	if (!(filp->f_mode & FMODE_WRITE))

fs/fhandle.c

@@ -201,7 +201,7 @@ static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 	struct handle_to_path_ctx *ctx = context;
 	struct user_namespace *user_ns = current_user_ns();
 	struct dentry *d, *root = ctx->root.dentry;
-	struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
 	int retval = 0;
 
 	if (!root)

fs/file_attr.c

@@ -323,7 +323,7 @@ int ioctl_getflags(struct file *file, unsigned int __user *argp)
 
 int ioctl_setflags(struct file *file, unsigned int __user *argp)
 {
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct dentry *dentry = file->f_path.dentry;
 	struct file_kattr fa = {};
 	unsigned int flags;
@@ -355,7 +355,7 @@ int ioctl_fsgetxattr(struct file *file, void __user *argp)
 
 int ioctl_fssetxattr(struct file *file, void __user *argp)
 {
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct dentry *dentry = file->f_path.dentry;
 	struct file_kattr fa = {};
 	int err;

fs/fuse/dir.c

@@ -941,7 +941,7 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
 			    umode_t mode)
 {
 	int err;
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct fuse_conn *fc = get_fuse_conn(dir);
 
 	if (fuse_is_bad(dir))

fs/fuse/file.c

@@ -1487,7 +1487,7 @@ static const struct iomap_write_ops fuse_iomap_write_ops = {
 static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct address_space *mapping = file->f_mapping;
 	ssize_t written = 0;
 	struct inode *inode = mapping->host;

fs/internal.h

@@ -327,7 +327,7 @@ ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *po
  * fs/attr.c
  */
 struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);
-struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap);
+const struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap);
 void mnt_idmap_put(const struct mnt_idmap *idmap);
 struct stashed_operations {
 	struct dentry *(*stash_dentry)(struct dentry **stashed,

fs/mnt_idmapping.c

@@ -312,14 +312,14 @@ struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns)
  *
  * Return: @idmap with reference count bumped if @not_mnt_idmap isn't passed.
  */
-struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap)
+const struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap)
 {
 	struct mnt_idmap *nonconst_idmap = (struct mnt_idmap *)idmap;
 
 	if (idmap != &nop_mnt_idmap && idmap != &invalid_mnt_idmap)
 		refcount_inc(&nonconst_idmap->count);
 
-	return nonconst_idmap;
+	return idmap;
 }
 EXPORT_SYMBOL_GPL(mnt_idmap_get);
 

fs/namei.c

@@ -1273,7 +1273,7 @@ fs_initcall(init_fs_namei_sysctls);
  */
 static inline int may_follow_link(struct nameidata *nd, const struct inode *inode)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	vfsuid_t vfsuid;
 
 	if (!sysctl_protected_symlinks)
@@ -2596,7 +2596,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
 
 	/* At this point we know we have a real path component. */
 	for(;;) {
-		struct mnt_idmap *idmap;
+		const struct mnt_idmap *idmap;
 		const char *link;
 		unsigned long lastword;
 
@@ -4432,7 +4432,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 				  const struct open_flags *op)
 {
 	struct delegated_inode delegated_inode = { };
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct dentry *dir = nd->path.dentry;
 	struct inode *dir_inode = dir->d_inode;
 	int open_flag;
@@ -4789,7 +4789,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 static int do_open(struct nameidata *nd,
 		   struct file *file, const struct open_flags *op)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	int open_flag = op->open_flag;
 	bool do_truncate;
 	int acc_mode;
@@ -5169,7 +5169,7 @@ struct file *dentry_create(struct path *path, int flags, umode_t mode,
 	struct dentry *orig_dentry = dentry;
 	struct dentry *dir = dentry->d_parent;
 	struct inode *dir_inode = d_inode(dir);
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	int error, create_error;
 
 	file = alloc_empty_file(flags, cred);
@@ -5294,7 +5294,7 @@ int filename_mknodat(int dfd, struct filename *name, umode_t mode,
 		     unsigned int dev)
 {
 	struct delegated_inode di = { };
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct dentry *dentry;
 	struct path path;
 	int error;
@@ -5949,7 +5949,7 @@ EXPORT_SYMBOL(vfs_link);
 int filename_linkat(int olddfd, struct filename *old,
 		    int newdfd, struct filename *new, int flags)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct dentry *new_dentry;
 	struct path old_path, new_path;
 	struct delegated_inode delegated_inode = { };

fs/namespace.c

@@ -109,7 +109,7 @@ struct mount_kattr {
 	unsigned int lookup_flags;
 	enum mount_kattr_flags_t kflags;
 	struct user_namespace *mnt_userns;
-	struct mnt_idmap *mnt_idmap;
+	const struct mnt_idmap *mnt_idmap;
 };
 
 /* /sys/fs */
@@ -4898,7 +4898,7 @@ static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt)
 
 static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
 {
-	struct mnt_idmap *old_idmap;
+	const struct mnt_idmap *old_idmap;
 
 	if (!kattr->mnt_idmap)
 		return;
@@ -4941,7 +4941,7 @@ static int do_mount_setattr(const struct path *path, struct mount_kattr *kattr)
 		return -EINVAL;
 
 	if (kattr->mnt_userns) {
-		struct mnt_idmap *mnt_idmap;
+		const struct mnt_idmap *mnt_idmap;
 
 		mnt_idmap = alloc_mnt_idmap(kattr->mnt_userns);
 		if (IS_ERR(mnt_idmap))
@@ -5246,7 +5246,7 @@ struct kstatmount {
 	struct statmount __user *buf;
 	size_t bufsize;
 	struct vfsmount *mnt;
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	u64 mask;
 	struct path root;
 	struct seq_file seq;

fs/open.c

@@ -72,7 +72,7 @@ int do_truncate(const struct mnt_idmap *idmap, struct dentry *dentry,
 
 int vfs_truncate(const struct path *path, loff_t length)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct inode *inode;
 	int error;
 
@@ -787,7 +787,7 @@ static inline bool setattr_vfsgid(struct iattr *attr, kgid_t kgid)
 
 int chown_common(const struct path *path, uid_t user, gid_t group)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct user_namespace *fs_userns;
 	struct inode *inode = path->dentry->d_inode;
 	struct delegated_inode delegated_inode = { };

fs/overlayfs/file.c

@@ -30,7 +30,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 {
 	struct inode *realinode = d_inode(realpath->dentry);
 	struct inode *inode = file_inode(file);
-	struct mnt_idmap *real_idmap;
+	const struct mnt_idmap *real_idmap;
 	struct file *realfile;
 	int flags = file->f_flags | OVL_OPEN_FLAGS;
 	int acc_mode = ACC_MODE(flags);

fs/overlayfs/inode.c

@@ -406,7 +406,7 @@ struct posix_acl *ovl_get_acl_path(const struct path *path,
 				   const char *acl_name, bool noperm)
 {
 	struct posix_acl *real_acl, *clone;
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct inode *realinode = d_inode(path->dentry);
 
 	idmap = mnt_idmap(path->mnt);

fs/overlayfs/ovl_entry.h

@@ -105,7 +105,7 @@ static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
 	return ofs->layers[0].mnt;
 }
 
-static inline struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
+static inline const struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
 {
 	return mnt_idmap(ovl_upper_mnt(ofs));
 }

fs/overlayfs/util.c

@@ -657,7 +657,7 @@ bool ovl_path_is_whiteout(struct ovl_fs *ofs, const struct path *path)
 struct file *ovl_path_open(const struct path *path, int flags)
 {
 	struct inode *inode = d_inode(path->dentry);
-	struct mnt_idmap *real_idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *real_idmap = mnt_idmap(path->mnt);
 	int err, acc_mode;
 
 	if (flags & ~(O_ACCMODE | O_LARGEFILE))
@@ -1496,7 +1496,7 @@ void ovl_copyattr(struct inode *inode)
 {
 	struct path realpath;
 	struct inode *realinode;
-	struct mnt_idmap *real_idmap;
+	const struct mnt_idmap *real_idmap;
 	vfsuid_t vfsuid;
 	vfsgid_t vfsgid;
 

fs/remap_range.c

@@ -415,7 +415,7 @@ EXPORT_SYMBOL(vfs_clone_file_range);
 /* Check whether we are allowed to dedupe the destination file */
 static bool may_dedupe_file(struct file *file)
 {
-	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	const struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct inode *inode = file_inode(file);
 
 	if (capable(CAP_SYS_ADMIN))

fs/smb/server/oplock.c

@@ -2229,7 +2229,7 @@ void create_posix_rsp_buf(char *cc, struct ksmbd_file *fp)
 {
 	struct create_posix_rsp *buf;
 	struct inode *inode = file_inode(fp->filp);
-	struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
 	vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
 	vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
 

fs/smb/server/smb2pdu.c

@@ -3234,7 +3234,7 @@ static bool smb2_is_private_ea(const char *name, size_t name_len)
 static int smb2_set_ea(struct smb2_ea_info *eabuf, unsigned int buf_len,
 		       const struct path *path, bool get_write)
 {
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	char *attr_name = NULL, *value;
 	int rc = 0;
 	unsigned int next = 0;
@@ -3335,7 +3335,7 @@ static noinline int smb2_set_stream_name_xattr(const struct path *path,
 					       struct ksmbd_file *fp,
 					       char *stream_name, int s_type)
 {
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	size_t xattr_stream_size;
 	char *xattr_stream_name;
 	int rc;
@@ -3411,7 +3411,7 @@ static loff_t ksmbd_stream_eof(struct ksmbd_file *fp)
 
 static int smb2_remove_smb_xattrs(const struct path *path)
 {
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	char *name, *xattr_list = NULL;
 	ssize_t xattr_list_len;
 	int err = 0;
@@ -4088,7 +4088,7 @@ int smb2_open(struct ksmbd_work *work)
 	struct ksmbd_share_config *share = tcon->share_conf;
 	struct ksmbd_file *fp = NULL;
 	struct file *filp = NULL;
-	struct mnt_idmap *idmap = NULL;
+	const struct mnt_idmap *idmap = NULL;
 	struct kstat stat;
 	struct create_context *context;
 	struct lease_ctx_info *lc = NULL;
@@ -5753,7 +5753,7 @@ struct smb2_query_dir_private {
 
 static int process_query_dir_entries(struct smb2_query_dir_private *priv)
 {
-	struct mnt_idmap	*idmap = file_mnt_idmap(priv->dir_fp->filp);
+	const struct mnt_idmap	*idmap = file_mnt_idmap(priv->dir_fp->filp);
 	struct kstat		kstat;
 	struct ksmbd_kstat	ksmbd_kstat;
 	int			rc;
@@ -6352,7 +6352,7 @@ static int smb2_get_ea(struct ksmbd_work *work, struct ksmbd_file *fp,
 	ssize_t buf_free_len, alignment_bytes, next_offset, rsp_data_cnt = 0;
 	struct smb2_ea_info_req *ea_req = NULL;
 	const struct path *path;
-	struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
 
 	if (!(fp->daccess & FILE_READ_EA_LE)) {
 		pr_err("Not permitted to read ext attr : 0x%x\n",
@@ -7062,7 +7062,7 @@ static int find_file_posix_info(struct smb2_query_info_rsp *rsp,
 {
 	struct smb311_posix_qinfo *file_info;
 	struct inode *inode = file_inode(fp->filp);
-	struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
 	vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
 	vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
 	struct kstat stat;
@@ -7547,7 +7547,7 @@ static int smb2_get_info_sec(struct ksmbd_work *work,
 			     struct smb2_query_info_rsp *rsp)
 {
 	struct ksmbd_file *fp;
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct smb_ntsd *pntsd = NULL, *ppntsd = NULL;
 	struct smb_fattr fattr = {{0}};
 	struct inode *inode;
@@ -8060,7 +8060,7 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 	struct iattr attrs;
 	struct file *filp;
 	struct inode *inode;
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	__le32 attrs_mask = FILE_ATTRIBUTE_DIRECTORY_LE |
 		FILE_ATTRIBUTE_COMPRESSED_LE;
 	int rc = 0;
@@ -10652,7 +10652,7 @@ static inline int fsctl_set_sparse(struct ksmbd_work *work, u64 id,
 				   struct file_sparse *sparse)
 {
 	struct ksmbd_file *fp;
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	int ret = 0;
 	__le32 old_fattr;
 

fs/smb/server/smb_common.c

@@ -467,7 +467,7 @@ int ksmbd_populate_dot_dotdot_entries(struct ksmbd_work *work, int info_level,
 {
 	int i, rc = 0;
 	struct ksmbd_conn *conn = work->conn;
-	struct mnt_idmap *idmap = file_mnt_idmap(dir->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(dir->filp);
 
 	for (i = 0; i < 2; i++) {
 		struct kstat kstat;

fs/smb/server/smbacl.c

@@ -1183,7 +1183,7 @@ int smb_inherit_dacl(struct ksmbd_conn *conn,
 	struct smb_ntsd *parent_pntsd = NULL;
 	struct smb_sid owner_sid, group_sid;
 	struct dentry *parent = path->dentry->d_parent;
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	int inherited_flags = 0, flags = 0, i, nt_size = 0, pdacl_size;
 	int rc = 0, pntsd_type, ppntsd_size, acl_len, aces_size;
 	unsigned int dacloffset;
@@ -1438,7 +1438,7 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path,
 			__le32 *pdaccess, __le32 raw_daccess, int uid,
 			bool strict)
 {
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	struct smb_ntsd *pntsd = NULL;
 	struct smb_acl *pdacl;
 	struct posix_acl *posix_acls;
@@ -1660,7 +1660,7 @@ int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon,
 	int rc;
 	struct smb_fattr fattr = {{0}};
 	struct inode *inode = d_inode(path->dentry);
-	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
+	const struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	struct iattr newattrs;
 
 	fattr.cf_uid = INVALID_UID;

fs/smb/server/vfs.c

@@ -183,7 +183,7 @@ int ksmbd_vfs_create(struct ksmbd_work *work, const char *name, umode_t mode)
  */
 int ksmbd_vfs_mkdir(struct ksmbd_work *work, const char *name, umode_t mode)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct path path;
 	struct dentry *dentry, *d;
 	int err = 0;
@@ -386,7 +386,7 @@ static int ksmbd_vfs_stream_write(struct ksmbd_file *fp, char *buf, loff_t *pos,
 {
 	const struct cred *saved_cred;
 	char *stream_buf = NULL, *wbuf;
-	struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
 	size_t size;
 	ssize_t v_len;
 	int err = 0;
@@ -577,7 +577,7 @@ int ksmbd_vfs_fsync(struct ksmbd_work *work, u64 fid, u64 p_id)
  */
 int ksmbd_vfs_remove_file(struct ksmbd_work *work, const struct path *path)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct dentry *parent = path->dentry->d_parent;
 	int err;
 
@@ -1202,7 +1202,7 @@ int ksmbd_vfs_unlink(struct file *filp)
 	const struct cred *saved_cred;
 	int err = 0;
 	struct dentry *dir, *dentry = filp->f_path.dentry;
-	struct mnt_idmap *idmap = file_mnt_idmap(filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(filp);
 
 	saved_cred = override_creds(filp->f_cred);
 	err = mnt_want_write(filp->f_path.mnt);
@@ -2316,7 +2316,7 @@ static int __ksmbd_vfs_set_compression(struct ksmbd_work *work,
 	const struct cred *saved_cred = NULL;
 	struct file_kattr fa;
 	struct dentry *dentry = fp->filp->f_path.dentry;
-	struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
+	const struct mnt_idmap *idmap = file_mnt_idmap(fp->filp);
 	u32 flags;
 	__le32 old_fattr;
 	int rc;

fs/stat.c

@@ -181,7 +181,7 @@ EXPORT_SYMBOL_GPL(generic_fill_statx_atomic_writes);
 int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
 		      u32 request_mask, unsigned int query_flags)
 {
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct inode *inode = d_backing_inode(path->dentry);
 
 	memset(stat, 0, sizeof(*stat));

include/linux/fs.h

@@ -2459,7 +2459,7 @@ struct filename {
 static_assert(offsetof(struct filename, iname) % sizeof(long) == 0);
 static_assert(sizeof(struct filename) % 64 == 0);
 
-static inline struct mnt_idmap *file_mnt_idmap(const struct file *file)
+static inline const struct mnt_idmap *file_mnt_idmap(const struct file *file)
 {
 	return mnt_idmap(file->f_path.mnt);
 }

include/linux/mnt_idmapping.h

@@ -121,7 +121,7 @@ static inline bool vfsgid_eq_kgid(vfsgid_t vfsgid, kgid_t kgid)
 
 int vfsgid_in_group_p(vfsgid_t vfsgid);
 
-struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap);
+const struct mnt_idmap *mnt_idmap_get(const struct mnt_idmap *idmap);
 void mnt_idmap_put(const struct mnt_idmap *idmap);
 
 vfsuid_t make_vfsuid(const struct mnt_idmap *idmap,

include/linux/mount.h

@@ -59,10 +59,10 @@ struct vfsmount {
 	struct dentry *mnt_root;	/* root of the mounted tree */
 	struct super_block *mnt_sb;	/* pointer to superblock */
 	int mnt_flags;
-	struct mnt_idmap *mnt_idmap;
+	const struct mnt_idmap *mnt_idmap;
 } __randomize_layout;
 
-static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt)
+static inline const struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt)
 {
 	/* Pairs with smp_store_release() in do_idmap_mount(). */
 	return READ_ONCE(mnt->mnt_idmap);

net/unix/af_unix.c

@@ -1361,7 +1361,7 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr,
 	struct unix_sock *u = unix_sk(sk);
 	unsigned int new_hash, old_hash;
 	struct net *net = sock_net(sk);
-	struct mnt_idmap *idmap;
+	const struct mnt_idmap *idmap;
 	struct unix_address *addr;
 	struct dentry *dentry;
 	struct path parent;

security/apparmor/lsm.c

@@ -397,7 +397,7 @@ static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_d
 
 	label = begin_current_label_crit_section(&needput);
 	if (!unconfined(label)) {
-		struct mnt_idmap *idmap = mnt_idmap(old_dir->mnt);
+		const struct mnt_idmap *idmap = mnt_idmap(old_dir->mnt);
 		vfsuid_t vfsuid;
 		struct path old_path = { .mnt = old_dir->mnt,
 					 .dentry = old_dentry };
@@ -485,7 +485,7 @@ static int apparmor_file_open(struct file *file)
 
 	label = aa_get_newest_cred_label_condref(file->f_cred, &needput);
 	if (!unconfined(label)) {
-		struct mnt_idmap *idmap = file_mnt_idmap(file);
+		const struct mnt_idmap *idmap = file_mnt_idmap(file);
 		struct inode *inode = file_inode(file);
 		vfsuid_t vfsuid;
 		struct path_cond cond = {