[PATCH] vfs: missing inode operation should return a consistent error code

[Jori Koolstra]

Currently several different error codes are used in the VFS for
situations where the underlying filesystem does not support the
requested inode operation (such as mkdir, tmpfile, create, etc.)
Examples: create returns EACCES, mkdir EPERM, tmpfile EOPNOTSUPP,
fileattr_get ENOIOCTLCMD.

We should provide a sensible unified error code for these situations.
EOPNOTSUPP is already used for this both in the kernel (when lacking
tmpfile support) and in userland (e.g. glibc).[1] Restricting EOPNOTSUPP
to socket operations as POSIX suggests is not the current reality and
this was recently changed in the man page as well.[2]

vfs_fileattr_get|set return ENOIOCTLCMD, but this cannot be changed
since EOPNOTSUPP is already used to by underlying filesystems to indicate
that a flag is not supported. The change to EOPNOTSUPP was reverted by
4dd5b5ac089b ("Revert "fs: make vfs_fileattr_[get|set] return
-EOPNOTSUPP"")

[1]: https://lore.kernel.org/all/20260528-abnimmt-befreien-perspektive-a7930659fb40@brauner/
[2]: https://lore.kernel.org/linux-fsdevel/ahd3SmZZqnzP0-O2@devuan/T/#t

Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>
---
 fs/namei.c                       | 18 +++++++++---------
 include/uapi/asm-generic/errno.h |  2 +-
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index c7fac83c9a85..813419c340ad 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4192,7 +4192,7 @@ int vfs_create(struct mnt_idmap *idmap, struct dentry *dentry, umode_t mode,
 		return error;
 
 	if (!dir->i_op->create)
-		return -EACCES;	/* shouldn't it be ENOSYS? */
+		return -EOPNOTSUPP;
 
 	mode = vfs_prepare_mode(idmap, dir, mode, S_IALLUGO, S_IFREG);
 	error = security_inode_create(dir, dentry, mode);
@@ -4504,7 +4504,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 		file->f_mode |= FMODE_CREATED;
 		audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
 		if (!dir_inode->i_op->create) {
-			error = -EACCES;
+			error = -EOPNOTSUPP;
 			goto out_dput;
 		}
 
@@ -5102,7 +5102,7 @@ int vfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
 		return -EPERM;
 
 	if (!dir->i_op->mknod)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	mode = vfs_prepare_mode(idmap, dir, mode, mode, mode);
 	error = devcgroup_inode_mknod(mode, dev);
@@ -5241,7 +5241,7 @@ struct dentry *vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (error)
 		goto err;
 
-	error = -EPERM;
+	error = -EOPNOTSUPP;
 	if (!dir->i_op->mkdir)
 		goto err;
 
@@ -5345,7 +5345,7 @@ int vfs_rmdir(struct mnt_idmap *idmap, struct inode *dir,
 		return error;
 
 	if (!dir->i_op->rmdir)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	dget(dentry);
 	inode_lock(dentry->d_inode);
@@ -5479,7 +5479,7 @@ int vfs_unlink(struct mnt_idmap *idmap, struct inode *dir,
 		return error;
 
 	if (!dir->i_op->unlink)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	inode_lock(target);
 	if (IS_SWAPFILE(target))
@@ -5630,7 +5630,7 @@ int vfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 		return error;
 
 	if (!dir->i_op->symlink)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	error = security_inode_symlink(dir, dentry, oldname);
 	if (error)
@@ -5752,7 +5752,7 @@ int vfs_link(struct dentry *old_dentry, struct mnt_idmap *idmap,
 	if (HAS_UNMAPPED_ID(idmap, inode))
 		return -EPERM;
 	if (!dir->i_op->link)
-		return -EPERM;
+		return -EOPNOTSUPP;
 	if (S_ISDIR(inode->i_mode))
 		return -EPERM;
 
@@ -5961,7 +5961,7 @@ int vfs_rename(struct renamedata *rd)
 		return error;
 
 	if (!old_dir->i_op->rename)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	/*
 	 * If we are going to change the parent - check write permissions,
diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
index 92e7ae493ee3..7b5b71ae1b12 100644
--- a/include/uapi/asm-generic/errno.h
+++ b/include/uapi/asm-generic/errno.h
@@ -76,7 +76,7 @@
 #define	ENOPROTOOPT	92	/* Protocol not available */
 #define	EPROTONOSUPPORT	93	/* Protocol not supported */
 #define	ESOCKTNOSUPPORT	94	/* Socket type not supported */
-#define	EOPNOTSUPP	95	/* Operation not supported on transport endpoint */
+#define	EOPNOTSUPP	95	/* Operation not supported */
 #define	EPFNOSUPPORT	96	/* Protocol family not supported */
 #define	EAFNOSUPPORT	97	/* Address family not supported by protocol */
 #define	EADDRINUSE	98	/* Address already in use */

base-commit: 670b77dfebe7257adc0defbc48a4c43cfdf6c8f6
-- 
2.54.0