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1.\" $OpenBSD: fuse_reply_err.3,v 1.1 2026/02/01 20:02:58 helg Exp $
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3.\" Copyright (c) 2026 Helg Bredow <helg@openbsd.org>
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17.Dd $Mdocdate: February 1 2026 $
18.Dt FUSE_REPLY_ERR 3
19.Os
20.Sh NAME
21.Nm fuse_reply_err ,
22.Nm fuse_reply_buf ,
23.Nm fuse_reply_attr ,
24.Nm fuse_reply_open ,
25.Nm fuse_reply_write ,
26.Nm fuse_reply_entry ,
27.Nm fuse_reply_statfs ,
28.Nm fuse_reply_readlink
29.Nd send replies to FUSE requests
30.Sh SYNOPSIS
31.Lb libfuse
32.In fuse_lowlevel.h
33.Ft int
34.Fo fuse_reply_err
35.Fa "fuse_req_t req"
36.Fa "int errno"
37.Fc
38.Ft int
39.Fo fuse_reply_buf
40.Fa "fuse_req_t req"
41.Fa "const char *buf"
42.Fa "off_t size"
43.Fc
44.Ft int
45.Fo fuse_reply_attr
46.Fa "fuse_req_t req"
47.Fa "const struct stat *attr"
48.Fa "double attr_timeout"
49.Fc
50.Ft int
51.Fo fuse_reply_open
52.Fa "fuse_req_t req"
53.Fa "const struct fuse_file_info *fi"
54.Fc
55.Ft int
56.Fo fuse_reply_write
57.Fa "fuse_req_t req"
58.Fa "size_t count"
59.Fc
60.Ft int
61.Fo fuse_reply_entry
62.Fa "fuse_req_t req"
63.Fa "const struct fuse_entry_param *e"
64.Fc
65.Ft int
66.Fo fuse_reply_statfs
67.Fa "fuse_req_t req"
68.Fa "const struct statvfs *stbuf"
69.Fc
70.Ft int
71.Fo fuse_reply_readlink
72.Fa "fuse_req_t req"
73.Fa "char *linkname"
74.Fc
75.Sh DESCRIPTION
76These functions are used in the FUSE low-level API to send responses to
77requests received from the kernel.
78.Pp
79Once called, the request is considered handled and must not be replied to
80again.
81.Bl -tag -width Ds
82.It Fn fuse_reply_err "req" "errno"
83Send an error response to the request
84.Fa req .
85The
86.Fa errno
87parameter must be a valid (non-negated) error number, for example
88.Er ENOENT
89or
90.Er EACCES ..
91.Pp
92This is a valid response for all file system operations.
93.It Fn fuse_reply_buf "req" "buf" "size"
94Send a buffer
95.Fa buf
96of
97.Fa size
98bytes of data to the kernel.
99.Pp
100This is a valid response for
101.Fn read
102and
103.Fn readdir
104operations.
105.It Fn fuse_reply_attr "req" "attr" "attr_timeout"
106Replies with file attributes specified in
107.Fa attr ,
108valid for
109.Fa attr_timeout
110seconds.
111The
112.Ox
113kernel does not currently support attribute caching and
114.Fa attr_timeout
115will be ignored.
116.Pp
117This is a valid response for
118.Fn getattr
119and
120.Fn setattr
121operations.
122.It Fn fuse_reply_open "req" "ffi"
123Send a response to an open request with the file info structure
124.Fa ffi .
125Only the
126.Fa fh
127member of
128.Fa ffi
129is used.
130.Pp
131This is a valid response for
132.Fn open
133and
134.Fn opendir
135operations.
136.It Fn fuse_reply_write "req" "count"
137Reply to a write request with the
138.Fa count
139of bytes written.
140.Pp
141This is a valid response for the
142.Fn write
143operation.
144.It Fn fuse_reply_entry "req" "e"
145Reply to a lookup or other request that results in new file creation with
146the details of the new directory entry
147.Fa e ,
148which is defined as follows:
149.Bd -literal
150struct fuse_entry_param {
151 ino_t ino; /* inode number of the entry */
152 unsigned long generation; /* must be non-zero */
153 struct stat attr; /* attributes of the entry */
154 double attr_timeout; /* ignored */
155 double entry_timeout; /* ignored */
156};
157.Ed
158.Pp
159The
160.Ox
161kernel does not currently cache FUSE lookups or attributes and the
162.Fa attr_timeout
163and
164.Fa entry_timeout
165members are ignored.
166.Pp
167This is a valid response for the
168.Fn lookup ,
169.Fn mknod ,
170.Fn mkdir ,
171.Fn symlink , and
172.Fn link
173operations.
174.It Fn fuse_reply_statfs "req" "stbuf"
175Reply with file system statistics provided in
176.Fa stbuf .
177.Pp
178This is a valid response for the
179.Fn statfs
180operation.
181.It Fn fuse_reply_readlink "req" "link"
182Replies to a readlink request with the symbolic link path
183.Fa link .
184The target string cannot contain the NUL character.
185.Pp
186This is a valid response for the
187.Fn readlink
188operation.
189.El
190.Sh RETURN VALUES
191All functions return 0 on success.
192On failure, they return
193.Pf \- Va errno
194to indicate the error.
195.Sh SEE ALSO
196.Xr fuse_lowlevel_new 3
197.Sh STANDARDS
198These library functions conform to FUSE 2.6.
199.Sh HISTORY
200These library functions have been available since
201.Ox 7.9 .
202.Sh AUTHORS
203.An Helg Bredow Aq Mt helg@openbsd.org