.\" $OpenBSD: fuse_reply_err.3,v 1.1 2026/02/01 20:02:58 helg Exp $
.\"
.\" Copyright (c) 2026 Helg Bredow <helg@openbsd.org>
.\"
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.Dd $Mdocdate: February 1 2026 $
.Dt FUSE_REPLY_ERR 3
.Os
.Sh NAME
.Nm fuse_reply_err ,
.Nm fuse_reply_buf ,
.Nm fuse_reply_attr ,
.Nm fuse_reply_open ,
.Nm fuse_reply_write ,
.Nm fuse_reply_entry ,
.Nm fuse_reply_statfs ,
.Nm fuse_reply_readlink
.Nd send replies to FUSE requests
.Sh SYNOPSIS
.Lb libfuse
.In fuse_lowlevel.h
.Ft int
.Fo fuse_reply_err
.Fa "fuse_req_t req"
.Fa "int errno"
.Fc
.Ft int
.Fo fuse_reply_buf
.Fa "fuse_req_t req"
.Fa "const char *buf"
.Fa "off_t size"
.Fc
.Ft int
.Fo fuse_reply_attr
.Fa "fuse_req_t req"
.Fa "const struct stat *attr"
.Fa "double attr_timeout"
.Fc
.Ft int
.Fo fuse_reply_open
.Fa "fuse_req_t req"
.Fa "const struct fuse_file_info *fi"
.Fc
.Ft int
.Fo fuse_reply_write
.Fa "fuse_req_t req"
.Fa "size_t count"
.Fc
.Ft int
.Fo fuse_reply_entry
.Fa "fuse_req_t req"
.Fa "const struct fuse_entry_param *e"
.Fc
.Ft int
.Fo fuse_reply_statfs
.Fa "fuse_req_t req"
.Fa "const struct statvfs *stbuf"
.Fc
.Ft int
.Fo fuse_reply_readlink
.Fa "fuse_req_t req"
.Fa "char *linkname"
.Fc
.Sh DESCRIPTION
These functions are used in the FUSE low-level API to send responses to
requests received from the kernel.
.Pp
Once called, the request is considered handled and must not be replied to
again.
.Bl -tag -width Ds
.It Fn fuse_reply_err "req" "errno"
Send an error response to the request
.Fa req .
The
.Fa errno
parameter must be a valid (non-negated) error number, for example
.Er ENOENT
or
.Er EACCES ..
.Pp
This is a valid response for all file system operations.
.It Fn fuse_reply_buf "req" "buf" "size"
Send a buffer
.Fa buf
of
.Fa size
bytes of data to the kernel.
.Pp
This is a valid response for
.Fn read
and
.Fn readdir
operations.
.It Fn fuse_reply_attr "req" "attr" "attr_timeout"
Replies with file attributes specified in
.Fa attr ,
valid for
.Fa attr_timeout
seconds.
The
.Ox
kernel does not currently support attribute caching and
.Fa attr_timeout
will be ignored.
.Pp
This is a valid response for
.Fn getattr
and
.Fn setattr
operations.
.It Fn fuse_reply_open "req" "ffi"
Send a response to an open request with the file info structure
.Fa ffi .
Only the
.Fa fh
member of
.Fa ffi
is used.
.Pp
This is a valid response for
.Fn open
and
.Fn opendir
operations.
.It Fn fuse_reply_write "req" "count"
Reply to a write request with the
.Fa count
of bytes written.
.Pp
This is a valid response for the
.Fn write
operation.
.It Fn fuse_reply_entry "req" "e"
Reply to a lookup or other request that results in new file creation with
the details of the new directory entry
.Fa e ,
which is defined as follows:
.Bd -literal
struct fuse_entry_param {
    ino_t          ino;           /* inode number of the entry */
    unsigned long  generation;    /* must be non-zero */
    struct stat    attr;          /* attributes of the entry */
    double         attr_timeout;  /* ignored */
    double         entry_timeout; /* ignored */
};
.Ed
.Pp
The
.Ox
kernel does not currently cache FUSE lookups or attributes and the
.Fa attr_timeout
and
.Fa entry_timeout
members are ignored.
.Pp
This is a valid response for the
.Fn lookup ,
.Fn mknod ,
.Fn mkdir ,
.Fn symlink , and
.Fn link
operations.
.It Fn fuse_reply_statfs "req" "stbuf"
Reply with file system statistics provided in
.Fa stbuf .
.Pp
This is a valid response for the
.Fn statfs
operation.
.It Fn fuse_reply_readlink "req" "link"
Replies to a readlink request with the symbolic link path
.Fa link .
The target string cannot contain the NUL character.
.Pp
This is a valid response for the
.Fn readlink
operation.
.El
.Sh RETURN VALUES
All functions return 0 on success.
On failure, they return
.Pf \- Va errno
to indicate the error.
.Sh SEE ALSO
.Xr fuse_lowlevel_new 3
.Sh STANDARDS
These library functions conform to FUSE 2.6.
.Sh HISTORY
These library functions have been available since
.Ox 7.9 .
.Sh AUTHORS
.An Helg Bredow Aq Mt helg@openbsd.org