nfs: Implement fileattr_get for case sensitivity

An NFS server re-exporting an NFS mount point needs to report
the case sensitivity behavior of the underlying filesystem to
its clients. NFSD's attribute encoder obtains that information
by calling vfs_fileattr_get() on the lower filesystem, so the
NFS client must implement fileattr_get to surface what it
learned from its own server.

The NFS client already retrieves case sensitivity information
from servers during mount via PATHCONF (NFSv3) or the
FATTR4_CASE_INSENSITIVE/FATTR4_CASE_PRESERVING attributes
(NFSv4). Expose this information through fileattr_get by
reporting the FS_XFLAG_CASEFOLD and FS_XFLAG_CASENONPRESERVING
flags. NFSv2 lacks PATHCONF support, so mounts using that protocol
version default to standard POSIX behavior: case-sensitive and
case-preserving.

PATHCONF is now invoked unconditionally for NFSv2 and NFSv3 mounts
so the case-sensitivity capabilities are established even when the
user pins server->namelen with the namlen= mount option. That option
is orthogonal to case handling, and skipping PATHCONF because
namelen was already known would leave the caps unset.

The two capability bits carry opposite polarity because their POSIX
defaults differ. Most servers are case-sensitive and case-
preserving, matching "neither xflag set." NFS_CAP_CASE_INSENSITIVE
is set only when the server affirms case insensitivity, so "server
said no" and "server did not answer" both collapse to the case-
sensitive default. NFS_CAP_CASE_NONPRESERVING follows the same
pattern in the opposite direction: set only when the server affirms
that it does not preserve case, so that silence or a missing
attribute lands on the case-preserving default. The NFSv4 probe
checks res.attr_bitmask[0] to distinguish "server said false" from
"server omitted the attribute" before setting the bit.

Both capability bits are cleared before each probe so a remount,
an NFSv4 transparent state migration to a server with different
case semantics, or a probe whose reply does not arrive does not
retain stale capabilities from the prior probe.

Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260507-case-sensitivity-v14-10-e62cc8200435@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/nfs/client.c

@@ -914,6 +914,7 @@ static void nfs_server_set_fsinfo(struct nfs_server *server,
  */
 static int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *mntfh, struct nfs_fattr *fattr)
 {
+	struct nfs_pathconf pathinfo = { };
 	struct nfs_fsinfo fsinfo;
 	struct nfs_client *clp = server->nfs_client;
 	int error;
@@ -933,15 +934,23 @@ static int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *mntfh, str
 
 	nfs_server_set_fsinfo(server, &fsinfo);
 
-	/* Get some general file system info */
-	if (server->namelen == 0) {
-		struct nfs_pathconf pathinfo;
+	pathinfo.fattr = fattr;
+	nfs_fattr_init(fattr);
 
-		pathinfo.fattr = fattr;
-		nfs_fattr_init(fattr);
+	/* Clear before probing so a failed RPC does not retain stale bits. */
+	if (clp->rpc_ops->version < 4)
+		server->caps &= ~(NFS_CAP_CASE_INSENSITIVE |
+				  NFS_CAP_CASE_NONPRESERVING);
 
-		if (clp->rpc_ops->pathconf(server, mntfh, &pathinfo) >= 0)
+	if (clp->rpc_ops->pathconf(server, mntfh, &pathinfo) >= 0) {
+		if (server->namelen == 0)
 			server->namelen = pathinfo.max_namelen;
+		if (clp->rpc_ops->version < 4) {
+			if (pathinfo.case_insensitive)
+				server->caps |= NFS_CAP_CASE_INSENSITIVE;
+			if (!pathinfo.case_preserving)
+				server->caps |= NFS_CAP_CASE_NONPRESERVING;
+		}
 	}
 
 	if (clp->rpc_ops->discover_trunking != NULL &&

fs/nfs/inode.c

@@ -41,6 +41,7 @@
 #include <linux/freezer.h>
 #include <linux/uaccess.h>
 #include <linux/iversion.h>
+#include <linux/fileattr.h>
 
 #include "nfs4_fs.h"
 #include "callback.h"
@@ -1095,6 +1096,20 @@ int nfs_getattr(struct mnt_idmap *idmap, const struct path *path,
 }
 EXPORT_SYMBOL_GPL(nfs_getattr);
 
+int nfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+	struct inode *inode = d_inode(dentry);
+
+	if (nfs_server_capable(inode, NFS_CAP_CASE_INSENSITIVE)) {
+		fa->fsx_xflags |= FS_XFLAG_CASEFOLD;
+		fa->flags |= FS_CASEFOLD_FL;
+	}
+	if (nfs_server_capable(inode, NFS_CAP_CASE_NONPRESERVING))
+		fa->fsx_xflags |= FS_XFLAG_CASENONPRESERVING;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nfs_fileattr_get);
+
 static void nfs_init_lock_context(struct nfs_lock_context *l_ctx)
 {
 	refcount_set(&l_ctx->count, 1);

fs/nfs/internal.h

@@ -451,6 +451,9 @@ extern void nfs_set_cache_invalid(struct inode *inode, unsigned long flags);
 extern bool nfs_check_cache_invalid(struct inode *, unsigned long);
 extern int nfs_wait_bit_killable(struct wait_bit_key *key, int mode);
 
+struct file_kattr;
+int nfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa);
+
 #if IS_ENABLED(CONFIG_NFS_LOCALIO)
 /* localio.c */
 struct nfs_local_dio {

fs/nfs/namespace.c

@@ -246,11 +246,13 @@ nfs_namespace_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 const struct inode_operations nfs_mountpoint_inode_operations = {
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 const struct inode_operations nfs_referral_inode_operations = {
 	.getattr	= nfs_namespace_getattr,
 	.setattr	= nfs_namespace_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 static void nfs_expire_automounts(struct work_struct *work)

fs/nfs/nfs3proc.c

@@ -1053,6 +1053,7 @@ static const struct inode_operations nfs3_dir_inode_operations = {
 	.permission	= nfs_permission,
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 #ifdef CONFIG_NFS_V3_ACL
 	.listxattr	= nfs3_listxattr,
 	.get_inode_acl	= nfs3_get_acl,
@@ -1064,6 +1065,7 @@ static const struct inode_operations nfs3_file_inode_operations = {
 	.permission	= nfs_permission,
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 #ifdef CONFIG_NFS_V3_ACL
 	.listxattr	= nfs3_listxattr,
 	.get_inode_acl	= nfs3_get_acl,

fs/nfs/nfs3xdr.c

@@ -2276,8 +2276,11 @@ static int decode_pathconf3resok(struct xdr_stream *xdr,
 	if (unlikely(!p))
 		return -EIO;
 	result->max_link = be32_to_cpup(p++);
-	result->max_namelen = be32_to_cpup(p);
-	/* ignore remaining fields */
+	result->max_namelen = be32_to_cpup(p++);
+	p++;	/* ignore no_trunc */
+	p++;	/* ignore chown_restricted */
+	result->case_insensitive = be32_to_cpup(p++) != 0;
+	result->case_preserving = be32_to_cpup(p) != 0;
 	return 0;
 }
 

fs/nfs/nfs4proc.c

@@ -3933,7 +3933,8 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 		server->caps &=
 			~(NFS_CAP_ACLS | NFS_CAP_HARDLINKS | NFS_CAP_SYMLINKS |
 			  NFS_CAP_SECURITY_LABEL | NFS_CAP_FS_LOCATIONS |
-			  NFS_CAP_OPEN_XOR | NFS_CAP_DELEGTIME);
+			  NFS_CAP_OPEN_XOR | NFS_CAP_DELEGTIME |
+			  NFS_CAP_CASE_INSENSITIVE | NFS_CAP_CASE_NONPRESERVING);
 		server->fattr_valid = NFS_ATTR_FATTR_V4;
 		if (res.attr_bitmask[0] & FATTR4_WORD0_ACL &&
 				res.acl_bitmask & ACL4_SUPPORT_ALLOW_ACL)
@@ -3944,8 +3945,9 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 			server->caps |= NFS_CAP_SYMLINKS;
 		if (res.case_insensitive)
 			server->caps |= NFS_CAP_CASE_INSENSITIVE;
-		if (res.case_preserving)
-			server->caps |= NFS_CAP_CASE_PRESERVING;
+		if ((res.attr_bitmask[0] & FATTR4_WORD0_CASE_PRESERVING) &&
+		    !res.case_preserving)
+			server->caps |= NFS_CAP_CASE_NONPRESERVING;
 #ifdef CONFIG_NFS_V4_SECURITY_LABEL
 		if (res.attr_bitmask[2] & FATTR4_WORD2_SECURITY_LABEL)
 			server->caps |= NFS_CAP_SECURITY_LABEL;
@@ -10617,6 +10619,7 @@ static const struct inode_operations nfs4_dir_inode_operations = {
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
 	.listxattr	= nfs4_listxattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 static const struct inode_operations nfs4_file_inode_operations = {
@@ -10624,6 +10627,7 @@ static const struct inode_operations nfs4_file_inode_operations = {
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
 	.listxattr	= nfs4_listxattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 static struct nfs_server *nfs4_clone_server(struct nfs_server *source,

fs/nfs/proc.c

@@ -598,6 +598,7 @@ nfs_proc_pathconf(struct nfs_server *server, struct nfs_fh *fhandle,
 {
 	info->max_link = 0;
 	info->max_namelen = NFS2_MAXNAMLEN;
+	info->case_preserving = true;
 	return 0;
 }
 
@@ -718,12 +719,14 @@ static const struct inode_operations nfs_dir_inode_operations = {
 	.permission	= nfs_permission,
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 static const struct inode_operations nfs_file_inode_operations = {
 	.permission	= nfs_permission,
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 };
 
 const struct nfs_rpc_ops nfs_v2_clientops = {

fs/nfs/symlink.c

@@ -22,6 +22,8 @@
 #include <linux/mm.h>
 #include <linux/string.h>
 
+#include "internal.h"
+
 /* Symlink caching in the page cache is even more simplistic
  * and straight-forward than readdir caching.
  */
@@ -74,4 +76,5 @@ const struct inode_operations nfs_symlink_inode_operations = {
 	.get_link	= nfs_get_link,
 	.getattr	= nfs_getattr,
 	.setattr	= nfs_setattr,
+	.fileattr_get	= nfs_fileattr_get,
 };

include/linux/nfs_fs_sb.h

@@ -306,7 +306,7 @@ struct nfs_server {
 #define NFS_CAP_ATOMIC_OPEN	(1U << 4)
 #define NFS_CAP_LGOPEN		(1U << 5)
 #define NFS_CAP_CASE_INSENSITIVE	(1U << 6)
-#define NFS_CAP_CASE_PRESERVING	(1U << 7)
+#define NFS_CAP_CASE_NONPRESERVING	(1U << 7)
 #define NFS_CAP_REBOOT_LAYOUTRETURN	(1U << 8)
 #define NFS_CAP_OFFLOAD_STATUS	(1U << 9)
 #define NFS_CAP_ZERO_RANGE	(1U << 10)

include/linux/nfs_xdr.h

@@ -182,6 +182,8 @@ struct nfs_pathconf {
 	struct nfs_fattr	*fattr; /* Post-op attributes */
 	__u32			max_link; /* max # of hard links */
 	__u32			max_namelen; /* max name length */
+	bool			case_insensitive;
+	bool			case_preserving;
 };
 
 struct nfs4_change_info {