[PATCH RFC v5 05/16] fuse: make args->in_args[0] to be always the header

[Bernd Schubert <bschubert@ddn.com>]

This change sets up FUSE operations to have headers in args.in_args[0],
even for opcodes without an actual header. We do this to prepare for
cleanly separating payload from headers in the future.

For opcodes without a header, we use a zero-sized struct as a
placeholder. This approach:
- Keeps things consistent across all FUSE operations
- Will help with payload alignment later
- Avoids future issues when header sizes change

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
 fs/fuse/dax.c    | 13 ++++++++-----
 fs/fuse/dev.c    | 24 ++++++++++++++++++++----
 fs/fuse/dir.c    | 41 +++++++++++++++++++++++++++--------------
 fs/fuse/fuse_i.h |  7 +++++++
 fs/fuse/xattr.c  |  9 ++++++---
 5 files changed, 68 insertions(+), 26 deletions(-)

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index 12ef91d170bb3091ac35a33d2b9dc38330b00948..e459b8134ccb089f971bebf8da1f7fc5199c1271 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -237,14 +237,17 @@ static int fuse_send_removemapping(struct inode *inode,
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	struct fuse_mount *fm = get_fuse_mount(inode);
 	FUSE_ARGS(args);
+	struct fuse_zero_in zero_arg;
 
 	args.opcode = FUSE_REMOVEMAPPING;
 	args.nodeid = fi->nodeid;
-	args.in_numargs = 2;
-	args.in_args[0].size = sizeof(*inargp);
-	args.in_args[0].value = inargp;
-	args.in_args[1].size = inargp->count * sizeof(*remove_one);
-	args.in_args[1].value = remove_one;
+	args.in_numargs = 3;
+	args.in_args[0].size = sizeof(zero_arg);
+	args.in_args[0].value = &zero_arg;
+	args.in_args[1].size = sizeof(*inargp);
+	args.in_args[1].value = inargp;
+	args.in_args[2].size = inargp->count * sizeof(*remove_one);
+	args.in_args[2].value = remove_one;
 	return fuse_simple_request(fm, &args);
 }
 
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index dbc222f9b0f0e590ce3ef83077e6b4cff03cff65..6effef4073da3dad2f6140761eca98147a41d88d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1007,6 +1007,19 @@ static int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
 
 	for (i = 0; !err && i < numargs; i++)  {
 		struct fuse_arg *arg = &args[i];
+
+		/* zero headers */
+		if (arg->size == 0) {
+			if (WARN_ON_ONCE(i != 0)) {
+				if (cs->req)
+					pr_err_once(
+						"fuse: zero size header in opcode %d\n",
+						cs->req->in.h.opcode);
+				return -EINVAL;
+			}
+			continue;
+		}
+
 		if (i == numargs - 1 && argpages)
 			err = fuse_copy_pages(cs, arg->size, zeroing);
 		else
@@ -1662,6 +1675,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 	size_t args_size = sizeof(*ra);
 	struct fuse_args_pages *ap;
 	struct fuse_args *args;
+	struct fuse_zero_in zero_arg;
 
 	offset = outarg->offset & ~PAGE_MASK;
 	file_size = i_size_read(inode);
@@ -1688,7 +1702,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 	args = &ap->args;
 	args->nodeid = outarg->nodeid;
 	args->opcode = FUSE_NOTIFY_REPLY;
-	args->in_numargs = 2;
+	args->in_numargs = 3;
 	args->in_pages = true;
 	args->end = fuse_retrieve_end;
 
@@ -1715,9 +1729,11 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
 	}
 	ra->inarg.offset = outarg->offset;
 	ra->inarg.size = total_len;
-	args->in_args[0].size = sizeof(ra->inarg);
-	args->in_args[0].value = &ra->inarg;
-	args->in_args[1].size = total_len;
+	args->in_args[0].size = sizeof(zero_arg);
+	args->in_args[0].value = &zero_arg;
+	args->in_args[1].size = sizeof(ra->inarg);
+	args->in_args[1].value = &ra->inarg;
+	args->in_args[2].size = total_len;
 
 	err = fuse_simple_notify_reply(fm, args, outarg->notify_unique);
 	if (err)
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 2b0d4781f39484d50d1fd7f4f673d8b08c5fd7cf..6d67d7f8e6b4460c759df3fb293e169bcc78a897 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -172,12 +172,16 @@ static void fuse_lookup_init(struct fuse_conn *fc, struct fuse_args *args,
 			     u64 nodeid, const struct qstr *name,
 			     struct fuse_entry_out *outarg)
 {
+	struct fuse_zero_in zero_arg;
+
 	memset(outarg, 0, sizeof(struct fuse_entry_out));
 	args->opcode = FUSE_LOOKUP;
 	args->nodeid = nodeid;
-	args->in_numargs = 1;
-	args->in_args[0].size = name->len + 1;
-	args->in_args[0].value = name->name;
+	args->in_numargs = 2;
+	args->in_args[0].size = sizeof(zero_arg);
+	args->in_args[0].value = &zero_arg;
+	args->in_args[1].size = name->len + 1;
+	args->in_args[1].value = name->name;
 	args->out_numargs = 1;
 	args->out_args[0].size = sizeof(struct fuse_entry_out);
 	args->out_args[0].value = outarg;
@@ -915,16 +919,19 @@ static int fuse_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 static int fuse_symlink(struct mnt_idmap *idmap, struct inode *dir,
 			struct dentry *entry, const char *link)
 {
+	struct fuse_zero_in zero_arg;
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	unsigned len = strlen(link) + 1;
 	FUSE_ARGS(args);
 
 	args.opcode = FUSE_SYMLINK;
-	args.in_numargs = 2;
-	args.in_args[0].size = entry->d_name.len + 1;
-	args.in_args[0].value = entry->d_name.name;
-	args.in_args[1].size = len;
-	args.in_args[1].value = link;
+	args.in_numargs = 3;
+	args.in_args[0].size = sizeof(zero_arg);
+	args.in_args[0].value = &zero_arg;
+	args.in_args[1].size = entry->d_name.len + 1;
+	args.in_args[1].value = entry->d_name.name;
+	args.in_args[2].size = len;
+	args.in_args[2].value = link;
 	return create_new_entry(fm, &args, dir, entry, S_IFLNK);
 }
 
@@ -975,6 +982,7 @@ static void fuse_entry_unlinked(struct dentry *entry)
 
 static int fuse_unlink(struct inode *dir, struct dentry *entry)
 {
+	struct fuse_zero_in inarg;
 	int err;
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	FUSE_ARGS(args);
@@ -984,9 +992,11 @@ static int fuse_unlink(struct inode *dir, struct dentry *entry)
 
 	args.opcode = FUSE_UNLINK;
 	args.nodeid = get_node_id(dir);
-	args.in_numargs = 1;
-	args.in_args[0].size = entry->d_name.len + 1;
-	args.in_args[0].value = entry->d_name.name;
+	args.in_numargs = 2;
+	args.in_args[0].size = sizeof(inarg);
+	args.in_args[0].value = &inarg;
+	args.in_args[1].size = entry->d_name.len + 1;
+	args.in_args[1].value = entry->d_name.name;
 	err = fuse_simple_request(fm, &args);
 	if (!err) {
 		fuse_dir_changed(dir);
@@ -998,6 +1008,7 @@ static int fuse_unlink(struct inode *dir, struct dentry *entry)
 
 static int fuse_rmdir(struct inode *dir, struct dentry *entry)
 {
+	struct fuse_zero_in zero_arg;
 	int err;
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	FUSE_ARGS(args);
@@ -1007,9 +1018,11 @@ static int fuse_rmdir(struct inode *dir, struct dentry *entry)
 
 	args.opcode = FUSE_RMDIR;
 	args.nodeid = get_node_id(dir);
-	args.in_numargs = 1;
-	args.in_args[0].size = entry->d_name.len + 1;
-	args.in_args[0].value = entry->d_name.name;
+	args.in_numargs = 2;
+	args.in_args[0].size = sizeof(zero_arg);
+	args.in_args[0].value = &zero_arg;
+	args.in_args[1].size = entry->d_name.len + 1;
+	args.in_args[1].value = entry->d_name.name;
 	err = fuse_simple_request(fm, &args);
 	if (!err) {
 		fuse_dir_changed(dir);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index f2391961031374d8d55916c326c6472f0c03aae6..e2d1d90dfdb13b2c3e7de4789501ee45d3bf7794 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -941,6 +941,13 @@ struct fuse_mount {
 	struct rcu_head rcu;
 };
 
+/*
+ * Empty header for FUSE opcodes without specific header needs.
+ * Used as a placeholder in args->in_args[0] for consistency
+ * across all FUSE operations, simplifying request handling.
+ */
+struct fuse_zero_in {};
+
 static inline struct fuse_mount *get_fuse_mount_super(struct super_block *sb)
 {
 	return sb->s_fs_info;
diff --git a/fs/fuse/xattr.c b/fs/fuse/xattr.c
index 5b423fdbb13f8f17c3982e96dd0de836662092b0..2df1efd2e9bdb46571148f484d7927044f31c184 100644
--- a/fs/fuse/xattr.c
+++ b/fs/fuse/xattr.c
@@ -158,15 +158,18 @@ int fuse_removexattr(struct inode *inode, const char *name)
 	struct fuse_mount *fm = get_fuse_mount(inode);
 	FUSE_ARGS(args);
 	int err;
+	struct fuse_zero_in zero_arg;
 
 	if (fm->fc->no_removexattr)
 		return -EOPNOTSUPP;
 
 	args.opcode = FUSE_REMOVEXATTR;
 	args.nodeid = get_node_id(inode);
-	args.in_numargs = 1;
-	args.in_args[0].size = strlen(name) + 1;
-	args.in_args[0].value = name;
+	args.in_numargs = 2;
+	args.in_args[0].size = sizeof(zero_arg);
+	args.in_args[0].value = &zero_arg;
+	args.in_args[1].size = strlen(name) + 1;
+	args.in_args[1].value = name;
 	err = fuse_simple_request(fm, &args);
 	if (err == -ENOSYS) {
 		fm->fc->no_removexattr = 1;

-- 
2.43.0