From: Chuck Lever <chuck.lever@oracle.com>

The hard-coded MSDOS_SUPER_MAGIC check in nfsd3_proc_pathconf()
only recognizes FAT filesystems as case-insensitive. Modern
filesystems like F2FS, exFAT, and CIFS support case-insensitive
directories, but NFSv3 clients cannot discover this capability.

Query the export's actual case behavior through ->fileattr_get
instead. This allows NFSv3 clients to correctly handle case
sensitivity for any filesystem that implements the fileattr
interface. Filesystems without ->fileattr_get continue to report
the default POSIX behavior (case-sensitive, case-preserving).

This change assumes the ("fat: Implement fileattr_get for case
sensitivity") has been applied, which ensures FAT filesystems
report their case behavior correctly via the fileattr interface.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs3proc.c | 18 ++++++++++--------
 fs/nfsd/vfs.c      | 25 +++++++++++++++++++++++++
 fs/nfsd/vfs.h      |  2 ++
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 42adc5461db0..9be0aca01de0 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -717,17 +717,19 @@ nfsd3_proc_pathconf(struct svc_rqst *rqstp)
 
 	if (resp->status == nfs_ok) {
 		struct super_block *sb = argp->fh.fh_dentry->d_sb;
+		bool case_insensitive, case_preserving;
 
-		/* Note that we don't care for remote fs's here */
-		switch (sb->s_magic) {
-		case EXT2_SUPER_MAGIC:
+		if (sb->s_magic == EXT2_SUPER_MAGIC) {
 			resp->p_link_max = EXT2_LINK_MAX;
 			resp->p_name_max = EXT2_NAME_LEN;
-			break;
-		case MSDOS_SUPER_MAGIC:
-			resp->p_case_insensitive = 1;
-			resp->p_case_preserving  = 0;
-			break;
+		}
+
+		resp->status = nfsd_get_case_info(&argp->fh,
+						  &case_insensitive,
+						  &case_preserving);
+		if (resp->status == nfs_ok) {
+			resp->p_case_insensitive = case_insensitive;
+			resp->p_case_preserving = case_preserving;
 		}
 	}
 
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 168d3ccc8155..f077032b42c3 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -32,6 +32,7 @@
 #include <linux/writeback.h>
 #include <linux/security.h>
 #include <linux/sunrpc/xdr.h>
+#include <linux/fileattr.h>
 
 #include "xdr3.h"
 
@@ -2871,3 +2872,27 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
 
 	return err? nfserrno(err) : 0;
 }
+
+/**
+ * nfsd_get_case_info - get case sensitivity info for a file handle
+ * @fhp: file handle that has already been verified
+ * @case_insensitive: output, true if the filesystem is case-insensitive
+ * @case_preserving: output, true if the filesystem preserves case
+ *
+ * Returns nfs_ok on success, or an nfserr on failure.
+ */
+__be32
+nfsd_get_case_info(struct svc_fh *fhp, bool *case_insensitive,
+		   bool *case_preserving)
+{
+	struct file_kattr fa = {};
+	int err;
+
+	err = vfs_fileattr_get(fhp->fh_dentry, &fa);
+	if (err && err != -ENOIOCTLCMD)
+		return nfserrno(err);
+
+	*case_insensitive = fa.case_insensitive;
+	*case_preserving = !fa.case_nonpreserving;
+	return nfs_ok;
+}
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index e192dca4a679..1ff62eecec09 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -155,6 +155,8 @@ __be32		nfsd_readdir(struct svc_rqst *, struct svc_fh *,
 			     loff_t *, struct readdir_cd *, nfsd_filldir_t);
 __be32		nfsd_statfs(struct svc_rqst *, struct svc_fh *,
 				struct kstatfs *, int access);
+__be32		nfsd_get_case_info(struct svc_fh *fhp, bool *case_insensitive,
+				   bool *case_preserving);
 
 __be32		nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
 				struct dentry *dentry, int acc);
-- 
2.52.0