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.Dd January 14, 2003
.Dt FSCTL 2
.Os "Mac OS X"
.Sh NAME
.Nm fsctl
.Nd control filesystems
.Sh SYNOPSIS
.Fd #include <sys/attr.h>
.Fd #include <sys/ioctl.h>
.Ft int
.Fn fsctl "const char *path" "unsigned long request" "void *data" "unsigned long options"
.Sh DESCRIPTION
The
.Fn fsctl
function manipulates the filesystem controlling mounted volumes.
In particular, many filesystem-specific operating
characteristics of mounted filesystems may be controlled
with
.Fn fsctl
requests.
.Fn fsctl
requests can also be used to extract filesystem-specific
information for a mounted volumes.
.Pp
.Fa path
is the path name of any file within the mounted filesystem.
An  fsctl
.Fa request
has encoded in it whether the argument is an
.Dq in
parameter
or
.Dq out
parameter, and the size of the argument
.Fa data
in bytes.
Values for
.Fa request
are entirely filesystem-specific except for the following, defined in
.Ao Pa sys/fsctl.h Ac :
.Bd -literal  -offset indent
FSGETMOUNTINFOSIZE	/* Return size of mount info data */
.Ed
.Pp
Macros and defines used in specifying an fsctl
.Fa request
are the same as for
.Fn ioctl
requests and are located in the file
.Ao Pa sys/ioccom.h Ac .
.Fa options
may specify special flags for the processing of the
.Fn fsctl
call.  The options are specified by
.Em or Ns 'ing
the option values.  The only option currently defined is
.Bd -literal -offset indent
#define FSOPT_NOFOLLOW	0x00000001	/* Don't follow symlinks */
.Ed
.Pp
which is interpreted by the
.Fn fsctl
call to prevent following of symlinks.  The
.Fa options
argument is passed to the filesystem, which may define and handle
additional
.Fa options
bit values.
.Sh RETURN VALUES
.Pp
If an error has occurred, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn fsctl
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EFAULT
.Fa path
or
.Em data
points to an invalid address.
.It Bq Er EIO
An
.Tn I/O
error occurred while reading from or writing to the file system.
.It Bq Er EINVAL
.Fa request
or
.Fa data
is not valid.
.El
.Sh SEE ALSO
.Xr getattrlist 2 ,
.Xr ioctl 2 ,
.Xr setattrlist 2
.Sh HISTORY
The
.Fn fsctl
function call appeared in Mac OS X version 10.0.