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906c312bbf
The mntopts(3) functions support operations associated with a mount
point. The main purpose of this commit is to document the mntopts(3)
functions that now appear in 18 utilities in the base system. See
mntopts(3) for the documentation details.
The getmntopts() function appeared in 4.4BSD. The build_iovec(),
build_iovec_argf(), free_iovec(), checkpath(), and rmslashes()
functions were added with nmount(8) in FreeBSD 5.0. The getmntpoint()
and chkdoreload() functions are being added in this commit.
These functions should be in a library but for historic reasons are
in a file in the sources for the mount(8) program. Thus, to access
them the following lines need to be added to the Makefile of the
program wanting to use them:
SRCS+= getmntopts.c
MOUNT= ${SRCTOP}/sbin/mount
CFLAGS+= -I${MOUNT}
.PATH: ${MOUNT}
Once these changes have been MFC'ed to 13 they may be made into
a library.
Reviewed by: kib, gbe
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D37907
382 lines
8.7 KiB
Groff
382 lines
8.7 KiB
Groff
.\" Copyright (c) 2023 Marshall Kirk McKusick
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.\" Copyright (c) 1994 The Regents of the University of California.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getmntopts.3 8.3 (Berkeley) 3/30/95
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.\"
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.Dd January 19, 2023
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.Dt MNTOPTS 3
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.Os
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.Sh NAME
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.Nm getmntopts ,
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.Nm getmntpoint ,
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.Nm chkdoreload ,
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.Nm build_iovec ,
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.Nm build_iovec_argf ,
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.Nm free_iovec ,
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.Nm checkpath ,
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.Nm rmslashes
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.Nd "mount point operations"
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.Sh SYNOPSIS
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.In mntopts.h
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.Ft void
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.Fo getmntopts
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.Fa "const char *options" "const struct mntopt *mopts"
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.Fa "int *flagp" "int *altflagp"
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.Fc
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.Ft struct statfs *
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.Fn getmntpoint "const char *name"
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.Ft int
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.Fo chkdoreload
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.Fa "struct statfs *mntp"
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.Fa "void (*prtmsg)(const char *fmt, ...)"
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.Fc
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.Ft void
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.Fo build_iovec
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.Fa "struct iovec **iov" "int *iovlen" "const char *name" "void *val"
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.Fa "size_t len"
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.Fc
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.Ft void
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.Fo build_iovec_argf
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.Fa "struct iovec **iov" "int *iovlen" "const char *name"
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.Fa "const char *fmt" "..."
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.Fc
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.Ft void
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.Fn free_iovec "struct iovec **iov" "int *iovlen"
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.Ft int
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.Fn checkpath "const char *path" "char *resolved"
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.Ft void
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.Fn rmslashes "char *rrpin" "char *rrpout"
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.Sh DESCRIPTION
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The
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.Nm mntopts
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functions support operations associated with a mount point.
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For historic reasons are in a file in the sources for the
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.Xr mount 8
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program.
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Thus, to access them the following lines need to be added to the
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.Nm Makefile
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of the program wanting to use them:
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.Bd -literal
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SRCS+= getmntopts.c
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MOUNT= ${SRCTOP}/sbin/mount
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CFLAGS+= -I${MOUNT}
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\&.PATH: ${MOUNT}
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.Ed
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.Pp
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The
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.Fn getmntopts
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function takes a comma separated option list and a list
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of valid option names, and computes the bitmask
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corresponding to the requested set of options.
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.Pp
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The string
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.Fa options
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is broken down into a sequence of comma separated tokens.
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Each token is looked up in the table described by
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.Fa mopts
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and the bits in
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the word referenced by either
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.Fa flagp
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or
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.Fa altflagp
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(depending on the
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.Va m_altloc
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field of the option's table entry)
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are updated.
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The flag words are not initialized by
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.Fn getmntopts .
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The table,
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.Fa mopts ,
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has the following format:
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.Bd -literal
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struct mntopt {
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char *m_option; /* option name */
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int m_inverse; /* is this a negative option, e.g., "dev" */
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int m_flag; /* bit to set, e.g., MNT_RDONLY */
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int m_altloc; /* non-zero to use altflagp rather than flagp */
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};
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.Ed
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.Pp
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The members of this structure are:
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.Bl -tag -width m_inverse
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.It Va m_option
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the option name,
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for example
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.Dq Li suid .
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.It Va m_inverse
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tells
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.Fn getmntopts
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that the name has the inverse meaning of the
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bit.
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For example,
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.Dq Li suid
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is the string, whereas the
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mount flag is
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.Dv MNT_NOSUID .
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In this case, the sense of the string and the flag
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are inverted, so the
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.Va m_inverse
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flag should be set.
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.It Va m_flag
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the value of the bit to be set or cleared in
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the flag word when the option is recognized.
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The bit is set when the option is discovered,
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but cleared if the option name was preceded
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by the letters
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.Dq Li no .
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The
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.Va m_inverse
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flag causes these two operations to be reversed.
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.It Va m_altloc
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the bit should be set or cleared in
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.Fa altflagp
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rather than
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.Fa flagp .
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.El
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.Pp
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Each of the user visible
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.Dv MNT_
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flags has a corresponding
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.Dv MOPT_
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macro which defines an appropriate
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.Vt "struct mntopt"
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entry.
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To simplify the program interface and ensure consistency across all
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programs, a general purpose macro,
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.Dv MOPT_STDOPTS ,
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is defined which
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contains an entry for all the generic VFS options.
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In addition, the macros
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.Dv MOPT_FORCE
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and
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.Dv MOPT_UPDATE
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exist to enable the
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.Dv MNT_FORCE
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and
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.Dv MNT_UPDATE
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flags to be set.
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Finally, the table must be terminated by an entry with a
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.Dv NULL
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first element.
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.Pp
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The
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.Fn getmntpoint
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function takes the pathname of a possible mount point
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or of a device (with or without
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.Pa /dev/
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prepended to it).
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If the pathname is a directory or a file,
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.Fn getmntpoint
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checks to see if the mount point currently has a filesystem
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mounted on it.
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If the pathname is a device,
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.Fn getmntpoint
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checks to see if it is currently mounted.
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If there is an associated mount, a pointer to a
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.Vt "struct statfs"
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is returned.
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The returned result is stored in a static buffer that is over-written
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each time the
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.Fn getmntpoint
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function or the
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.Xr getmntinfo 3
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library routine is called.
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If no mount is found, NULL is returned.
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.Pp
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The
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.Fn chkdoreload
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function takes a pointer to a
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.Vt "struct statfs" .
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If the filesystem associated with the mount point is mounted read-only,
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.Fn chkdoreload
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requests the filesystem to reload all of its metadata from its backing store.
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The second parameter is the function to call to print an error message
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if the reload fails.
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If no error message is desired, a
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.Dv NULL
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can be passed as the second argument.
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The
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.Fn chkdoreload
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function returns zero on success or non-zero on failure.
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.Pp
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The
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.Fn build_iovec
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function adds a parameter to a list of parameters to be passed to the
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.Xr nmount 2
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system call.
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The parameter list is built up in
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.Va iov
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and its length is kept in
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.Va iovlen .
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Before the first call to
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.Fn build_iovec ,
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.Va iov
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should be set to
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.Dv NULL
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and
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.Va iovlen
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should be set to 0.
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The parameter name is passed in
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.Va name .
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The value of the parameter name is pointed to by
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.Va val .
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The size of the value is passed in
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.Va len .
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If the value is a string, a
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.Va len
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of -1 is passed to indicate that the length should be determined using
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.Xr strlen 3 .
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If the parameter has no value,
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.Va name
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should be
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.Dv NULL
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and
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.Va len
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should be 0.
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.Pp
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The
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.Fn build_iovec_argf
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function adds a formatted parameter to a list of parameters to be passed
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to the
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.Xr nmount 2
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system call.
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The parameter list is built up in
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.Va iov
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and its length is kept in
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.Va iovlen .
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Before the first call to
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.Fn build_iovec_argf ,
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.Va iov
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should be set to
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.Dv NULL
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and
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.Va iovlen
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should be set to 0.
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The parameter name is passed in
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.Va name .
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The value of the parameter name is described by a format string pointed to by
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.Va fmt .
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If the parameter has no value,
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.Va name
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should be
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.Dv NULL .
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.Pp
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The
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.Fn free_iovec
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function frees the memory in the
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.Va iov
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vector of the length specified in
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.Va iovlen
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that was previously allocated by the
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.Fn build_iovec
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and / or
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.Fn build_iovec_argf
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functions.
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The
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.Va iov
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is set to
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.Dv NULL
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and the
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.Va iovlen
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is set to 0 to indicate that the space has been freed.
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.Pp
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The
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.Fn checkpath
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function uses
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.Xr realpath 3
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to verify that its
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.Va path
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argument is valid and references a directory.
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The
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.Fn checkpath
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function returns zero on success or non-zero on failure.
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.Pp
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The
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.Fn rmslashes
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function removes all double slashes and trailing slashes from its
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.Va rrpin
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pathname parameter and returns the resulting pathname in its
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.Va rrpout
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parameter.
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.Sh EXAMPLES
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Most commands will use the standard option set.
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Local file systems which support the
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.Dv MNT_UPDATE
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flag, would also have an
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.Dv MOPT_UPDATE
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entry.
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This can be declared and used as follows:
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.Bd -literal
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#include "mntopts.h"
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struct mntopt mopts[] = {
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MOPT_STDOPTS,
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MOPT_UPDATE,
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{ NULL }
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};
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...
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mntflags = mntaltflags = 0;
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...
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getmntopts(options, mopts, &mntflags, &mntaltflags);
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...
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.Ed
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.Sh DIAGNOSTICS
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If the external integer variable
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.Va getmnt_silent
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is zero, then the
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.Fn getmntopts
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function displays an error message and exits if an
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unrecognized option is encountered.
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Otherwise unrecognized options are silently ignored.
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By default
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.Va getmnt_silent
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is zero.
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.Sh SEE ALSO
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.Xr err 3 ,
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.Xr mount 8 ,
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.Xr nmount 8
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.Sh HISTORY
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The
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.Fn getmntopts
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function appeared in
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.Bx 4.4 .
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The
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.Fn build_iovec ,
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.Fn build_iovec_argf ,
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.Fn free_iovec ,
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.Fn checkpath ,
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and
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.Fn rmslashes
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functions were added with
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.Xr nmount 8
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in
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.Fx 5.0 .
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The
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.Fn getmntpoint
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and
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.Fn chkdoreload
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functions were added in
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.Fx 14.0 .
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