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380 lines
8.7 KiB
Groff
380 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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.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 13.2 .
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