---
name: "vfs_copyopt"
section: "9"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/vfs_copyopt"
---

# vfs\_copyopt(9)

manipulate mount options and their values

## NAME

**vfs\_getopt**, **vfs\_getopts**, **vfs\_flagopt**, **vfs\_scanopt**, **vfs\_copyopt**, **vfs\_filteropt**, **vfs\_setopt**, **vfs\_setopt\_part**, **vfs\_setopts** – manipulate mount options and their values

## SYNOPSIS

**#include \<sys/param.h\>**

**#include \<sys/mount.h\>**

*int*\

**vfs\_getopt**(*struct vfsoptlist \*opts*, *const char \*name*, *void \*\*buf*, *int \*len*);

*char \**\

**vfs\_getopts**(*struct vfsoptlist \*opts*, *const char \*name*, *int \*error*);

*int*\

**vfs\_flagopt**(*struct vfsoptlist \*opts*, *const char \*name*, *uint64\_t \*flags*, *uint64\_t flag*);

*int*\

**vfs\_scanopt**(*struct vfsoptlist \*opts*, *const char \*name*, *const char \*fmt*, *...*);

*int*\

**vfs\_copyopt**(*struct vfsoptlist \*opts*, *const char \*name*, *void \*dest*, *int len*);

*int*\

**vfs\_filteropt**(*struct vfsoptlist \*opts*, *const char \*\*legal*);

*int*\

**vfs\_setopt**(*struct vfsoptlist \*opts*, *const char \*name*, *void \*value*, *int len*);

*int*\

**vfs\_setopt\_part**(*struct vfsoptlist \*opts*, *const char \*name*, *void \*value*, *int len*);

*int*\

**vfs\_setopts**(*struct vfsoptlist \*opts*, *const char \*name*, *const char \*value*);

## DESCRIPTION

The **vfs\_getopt**() function sets *buf* to point to the value of the named mount option, and sets *len* to the length of the value if it is not NULL. The *buf* argument will point to the actual value, and does not need to be freed or released (and probably should not be modified).

The **vfs\_getopts**() function returns the value of the specified option if it is a string (i.e., NUL terminated).

The **vfs\_flagopt**() function determines if an option exists. If the option does exist, and *flags* is not NULL, *flag* is added to those already set in *flags*. If the option does not exist, and *flags* is not NULL, *flag* is removed from those already set in *flags*. An example of typical usage is:

```
if (vfs_flagopt(mp->mnt_optnew, "wormlike", NULL, 0))
	vfs_flagopt(mp->mnt_optnew, "appendok", &(mp->flags), F_APPENDOK);
```

The **vfs\_scanopt**() function performs a [vsscanf(3)](/vsscanf/3.md) with the option's value, using the given format, into the specified variable arguments. The value must be a string (i.e., NUL terminated).

The **vfs\_copyopt**() function creates a copy of the option's value. The *len* argument must match the length of the option's value exactly (i.e., a larger buffer will still cause **vfs\_copyout**() to fail with EINVAL).

The **vfs\_filteropt**() function ensures that no unknown options were specified. A option is valid if its name matches one of the names in the list of legal names. An option may be prefixed with 'no', and still be considered valid.

The **vfs\_setopt**() and **vfs\_setopt\_part**() functions copy new data into the option's value. In **vfs\_setopt**(), the *len* argument must match the length of the option's value exactly (i.e., a larger buffer will still cause **vfs\_copyout**() to fail with EINVAL).

The **vfs\_setopts**() function copies a new string into the option's value. The string, including NUL byte, must be no longer than the option's length.

## RETURN VALUES

The **vfs\_getopt**() function returns 0 if the option was found; otherwise, ENOENT is returned.

The **vfs\_getopts**() function returns the specified option if it is found, and is NUL terminated. If the option was found, but is not NUL terminated, *error* is set to EINVAL and NULL is returned. If the option was not found, *error* is set to 0, and NULL is returned.

The **vfs\_flagopt**() function returns 1 if the option was found, and 0 if it was not.

The **vfs\_scanopt**() function returns 0 if the option was not found, or was not NUL terminated; otherwise, the return value of [vsscanf(3)](/vsscanf/3.md) is returned. If [vsscanf(3)](/vsscanf/3.md) returns 0, it will be returned unchanged; therefore, a return value of 0 does not always mean the option does not exist, or is not a valid string.

The **vfs\_copyopt**() and **vfs\_setopt**() functions return 0 if the copy was successful, EINVAL if the option was found but the lengths did not match, and ENOENT if the option was not found.

The **vfs\_filteropt**() function returns 0 if all of the options are legal; otherwise, EINVAL is returned.

The **vfs\_setopts**() function returns 0 if the copy was successful, EINVAL if the option was found but the string was too long, and ENOENT if the option was not found.

## AUTHORS

This manual page was written by Chad David ⟨*davidc@FreeBSD.org*⟩ and Ruslan Ermilov ⟨*ru@FreeBSD.org*⟩.