[RFC PATCH v3 8/8] fuse: implementation of mkobj_handle+statx+open compound operation

[Luis Henriques <luis@igalia.com>]

The implementation of this compound operation allows atomic_open() to use
file handle.  It also introduces a new MKOBJ_HANDLE operation that will
handle the file system object creation and will return the file handle.

The atomicity of the operation (create + open) needs to be handled in
user-space (e.g. the handling of the O_EXCL flag).

Signed-off-by: Luis Henriques <luis@igalia.com>
---
 fs/fuse/dir.c             | 219 +++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/fuse.h |   2 +
 2 files changed, 220 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 7fa8c405f1a3..b5beb1d62c3d 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1173,6 +1173,220 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
 	return err;
 }
 
+static int fuse_mkobj_handle_init(struct fuse_mount *fm, struct fuse_args *args,
+				  struct mnt_idmap *idmap, struct inode *dir,
+				  struct dentry *entry, unsigned int flags,
+				  umode_t mode,
+				  struct fuse_create_in *inarg,
+				  struct fuse_entry2_out *outarg,
+				  struct fuse_file_handle **fh)
+{
+	struct fuse_inode *fi;
+	size_t fh_size = sizeof(struct fuse_file_handle) + MAX_HANDLE_SZ;
+	int err = 0;
+
+	*fh = kzalloc(fh_size, GFP_KERNEL);
+	if (!*fh)
+		return -ENOMEM;
+
+	memset(inarg, 0, sizeof(*inarg));
+	memset(outarg, 0, sizeof(*outarg));
+
+	inarg->flags = flags;
+	inarg->mode = mode;
+	inarg->umask = current_umask();
+
+	if (fm->fc->handle_killpriv_v2 && (flags & O_TRUNC) &&
+	    !(flags & O_EXCL) && !capable(CAP_FSETID))
+		inarg->open_flags |= FUSE_OPEN_KILL_SUIDGID;
+
+	args->opcode = FUSE_MKOBJ_HANDLE;
+	args->nodeid = get_node_id(dir);
+	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 = get_create_ext(idmap, args, dir, entry, mode);
+	if (err)
+		goto out_err;
+	fi = get_fuse_inode(dir);
+	if (fi && fi->fh) {
+		if (!args->is_ext) {
+			args->is_ext = true;
+			args->ext_idx = args->in_numargs++;
+		}
+		err = create_ext_handle(&args->in_args[args->ext_idx], fi);
+		if (err)
+			goto out_err;
+	}
+
+	args->out_numargs = 2;
+	args->out_args[0].size = sizeof(*outarg);
+	args->out_args[0].value = outarg;
+	args->out_args[1].size = fh_size;
+	args->out_args[1].value = *fh;
+
+out_err:
+	if (err) {
+		kfree(*fh);
+		free_ext_value(args);
+	}
+
+	return err;
+}
+
+static int fuse_mkobj_statx_open(struct mnt_idmap *idmap, struct inode *dir,
+				 struct dentry *entry, struct file *file,
+				 unsigned int flags, umode_t mode)
+{
+	struct fuse_compound_req *compound;
+	struct fuse_mount *fm = get_fuse_mount(dir);
+	struct fuse_inode *fi = NULL;
+	struct fuse_create_in mkobj_in;
+	struct fuse_entry2_out mkobj_out;
+	struct fuse_statx_in statx_in;
+	struct fuse_statx_out statx_out;
+	struct fuse_open_in open_in;
+	struct fuse_open_out *open_outp;
+	FUSE_ARGS(mkobj_args);
+	FUSE_ARGS(statx_args);
+	FUSE_ARGS(open_args);
+	struct fuse_forget_link *forget;
+	struct fuse_file *ff;
+	struct fuse_attr attr;
+	struct fuse_file_handle *fh = NULL;
+	struct inode *inode;
+	int epoch, ret = -EIO;
+	int i;
+
+	epoch = atomic_read(&fm->fc->epoch);
+
+	ret = -ENOMEM;
+	forget = fuse_alloc_forget();
+	if (!forget)
+		return -ENOMEM;
+	ff = fuse_file_alloc(fm, true);
+	if (!ff)
+		goto out_forget;
+
+	if (!fm->fc->dont_mask)
+		mode &= ~current_umask();
+
+	flags &= ~O_NOCTTY;
+
+	compound = fuse_compound_alloc(fm, FUSE_COMPOUND_ATOMIC);
+	if (!compound)
+		goto out_free_ff;
+
+	fi = get_fuse_inode(dir);
+	if (!fi) {
+		ret = -EIO;
+		goto out_compound;
+	}
+	ret = fuse_mkobj_handle_init(fm, &mkobj_args, idmap, dir, entry, flags,
+				     mode, &mkobj_in, &mkobj_out, &fh);
+	if (ret)
+		goto out_compound;
+
+	ret = fuse_compound_add(compound, &mkobj_args);
+	if (ret)
+		goto out_mkobj_args;
+
+	fuse_statx_init(&statx_args, &statx_in, FUSE_ROOT_ID, NULL, &statx_out);
+	ret = fuse_compound_add(compound, &statx_args);
+	if (ret)
+		goto out_mkobj_args;
+
+	ff->fh = 0;
+	ff->open_flags = FOPEN_KEEP_CACHE;
+	memset(&open_in, 0, sizeof(open_in));
+
+	/* XXX flags handling */
+	open_in.flags = ff->open_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
+	if (!fm->fc->atomic_o_trunc)
+		open_in.flags &= ~O_TRUNC;
+	if (fm->fc->handle_killpriv_v2 &&
+	    (open_in.flags & O_TRUNC) && !capable(CAP_FSETID))
+		open_in.open_flags |= FUSE_OPEN_KILL_SUIDGID;
+
+	open_outp = &ff->args->open_outarg;
+	fuse_open_args_fill(&open_args, FUSE_ROOT_ID, FUSE_OPEN, &open_in,
+			    open_outp);
+
+	ret = fuse_compound_add(compound, &open_args);
+	if (ret)
+		goto out_mkobj_args;
+
+	ret = fuse_compound_send(compound);
+	if (ret)
+		goto out_mkobj_args;
+
+	for (i = 0; i < 3; i++) {
+		int err;
+
+		err = fuse_compound_get_error(compound, i);
+		if (err && !ret)
+			ret = err;
+	}
+	if (ret)
+		goto out_mkobj_args;
+
+	fuse_statx_to_attr(&statx_out.stat, &attr);
+	WARN_ON(fuse_invalid_attr(&attr));
+	ret = -EIO;
+	if (!S_ISREG(attr.mode) || invalid_nodeid(mkobj_out.nodeid) ||
+	    fuse_invalid_attr(&attr))
+		goto out_mkobj_args;
+
+	ff->fh = open_outp->fh;
+	ff->nodeid = mkobj_out.nodeid;
+	ff->open_flags = open_outp->open_flags;
+	inode = fuse_iget(dir->i_sb, mkobj_out.nodeid, mkobj_out.generation,
+			  &attr, ATTR_TIMEOUT(&statx_out), 0, 0, fh);
+	if (!inode) {
+		flags &= ~(O_CREAT | O_EXCL | O_TRUNC);
+		fuse_sync_release(NULL, ff, flags);
+		fuse_queue_forget(fm->fc, forget, mkobj_out.nodeid, 1);
+		ret = -ENOMEM;
+		goto out_mkobj_args;
+	}
+	d_instantiate(entry, inode);
+
+	entry->d_time = epoch;
+	fuse_dentry_settime(entry,
+		fuse_time_to_jiffies(mkobj_out.entry_valid,
+				     mkobj_out.entry_valid_nsec));
+	fuse_dir_changed(dir);
+	ret = generic_file_open(inode, file);
+	if (!ret) {
+		file->private_data = ff;
+		ret = finish_open(file, entry, fuse_finish_open);
+	}
+	if (ret) {
+		fuse_sync_release(get_fuse_inode(inode), ff, flags);
+	} else {
+		if (fm->fc->atomic_o_trunc && (flags & O_TRUNC))
+			truncate_pagecache(inode, 0);
+		else if (!(ff->open_flags & FOPEN_KEEP_CACHE))
+			invalidate_inode_pages2(inode->i_mapping);
+	}
+
+out_mkobj_args:
+	fuse_req_free_argvar_ext(&mkobj_args);
+out_compound:
+	kfree(compound);
+out_free_ff:
+	if (ret)
+		fuse_file_free(ff);
+out_forget:
+	kfree(forget);
+	kfree(fh);
+
+	return ret;
+}
+
 static int fuse_mknod(struct mnt_idmap *, struct inode *, struct dentry *,
 		      umode_t, dev_t);
 static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
@@ -1201,7 +1415,10 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
 	if (fc->no_create)
 		goto mknod;
 
-	err = fuse_create_open(idmap, dir, entry, file, flags, mode, FUSE_CREATE);
+	if (fc->lookup_handle)
+		err = fuse_mkobj_statx_open(idmap, dir, entry, file, flags, mode);
+	else
+		err = fuse_create_open(idmap, dir, entry, file, flags, mode, FUSE_CREATE);
 	if (err == -ENOSYS) {
 		fc->no_create = 1;
 		goto mknod;
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 89e6176abe25..f49eb1b8f2f3 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -243,6 +243,7 @@
  *
  *  7.46
  *  - add FUSE_LOOKUP_HANDLE
+ *  - add FUSE_MKOBJ_HANDLE
  */
 
 #ifndef _LINUX_FUSE_H
@@ -677,6 +678,7 @@ enum fuse_opcode {
 	FUSE_COMPOUND		= 54,
 
 	FUSE_LOOKUP_HANDLE	= 55,
+	FUSE_MKOBJ_HANDLE	= 56,
 
 	/* CUSE specific operations */
 	CUSE_INIT		= 4096,