getmntopts(3) - NetBSD Manual Pages

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GETMNTOPTS(3)           NetBSD Library Functions Manual          GETMNTOPTS(3)


NAME

     getmntopts, getmntoptstr, getmntoptnum, freemntopts -- scan mount options


LIBRARY

     System Utilities Library (libutil, -lutil)


SYNOPSIS

     #include <mntopts.h>

     mntoptparse_t
     getmntopts(const char *options, const struct mntopt *mopts, int *flagp,
         int *altflagp);

     const char *
     getmntoptstr(mntoptparse_t mp, const char *opt);

     long
     getmntoptnum(mntoptparse_t mp, const char *opt);

     void
     freemntopts(mntoptparse_t mp);


DESCRIPTION

     The getmntopts() function takes a comma separated option list and a list
     of valid option names, and computes the bitmasks corresponding to the
     requested set of options.

     The string options is broken down into a sequence of comma separated
     tokens.  Each token is looked up in the table described by mopts and the
     bits in the word referenced by either flagp or altflagp (depending on the
     m_altloc field of the option's table entry) are updated.  The flag words
     are not initialized by getmntopts().  The table, mopts, has the following
     format:

     struct mntopt {
             const char *m_option;   /* option name */
             int m_inverse;          /* negative option, e.g., "dev" */
             int m_flag;             /* bit to set, e.g., MNT_RDONLY */
             int m_altloc;           /* use altflagp rather than flagp */
     };

     The members of this structure are:

     m_option   the option name, for example ``suid''.

     m_inverse  tells getmntopts() that the name has the inverse meaning of
                the bit.  For example, ``suid'' is the string, whereas the
                mount flag is MNT_NOSUID.  In this case, the sense of the
                string and the flag are inverted, so the m_inverse flag should
                be set.

     m_flag     the value of the bit to be set or cleared in the flag word
                when the option is recognized.  The bit is set when the option
                is discovered, but cleared if the option name was preceded by
                the letters ``no''.  The m_inverse flag causes these two oper-
                ations to be reversed.

     m_altloc   the bit should be set or cleared in altflagp rather than
                flagp.

     Each of the user visible MNT_ flags has a corresponding MOPT_ macro which
     defines an appropriate struct mntopt entry.  To simplify the program
     interface and ensure consistency across all programs, a general purpose
     macro, MOPT_STDOPTS, is defined which contains an entry for all the
     generic VFS options.  In addition, the macros MOPT_FORCE and MOPT_UPDATE
     exist to enable the MNT_FORCE and MNT_UPDATE flags to be set.  Finally,
     the table must be terminated by an entry with a NULL first element.

     getmntopts() returns a mntoptparse_t handle that can be used in subse-
     quent getmntoptstr() and getmntoptnum() calls to fetch a value for an
     option and that must be freed with a call to freemntopts().  If an error
     occurred, then if the external integer value getmnt_silent is zero then
     getmntopts() prints an error message and exits; if getmnt_silent is non-
     zero then getmntopts() returns NULL.

     The getmntoptstr() function returns the string value of the named option,
     if such a value was set in the option string.  If the value was not set,
     then if the external integer value getmnt_silent is zero then
     getmntoptstr() prints an error message and exits; if getmnt_silent is
     non-zero then getmntoptstr() returns NULL.

     The getmntoptnum() function returns the long value of the named option,
     if such a value was set in the option string.  If the value was not set,
     or could not be converted from a string to a long, then if the external
     integer value getmnt_silent is zero then getmntoptnum() prints an error
     message and exits; if getmnt_silent is non-zero then getmntoptnum()
     returns -1.

     The freemntopts() function frees the storage used by getmntopts().


RETURN VALUES

     getmntopts() returns NULL if an error occurred.  Note that some bits may
     already have been set in flagp and altflagp even if NULL is returned.
     getmntoptstr() returns NULL if an error occurred.  getmntoptnum() returns
     -1 if an error occurred.


EXAMPLES

     Most commands will use the standard option set.  Local filesystems which
     support the MNT_UPDATE flag, would also have an MOPT_UPDATE entry.  This
     can be declared and used as follows:

           #include <mntopts.h>

           static const struct mntopt mopts[] = {
                   MOPT_STDOPTS,
                   MOPT_UPDATE,
                   { NULL }
           };

           ...

           long val;
           mntoptparse_t mp;
           mntflags = mntaltflags = 0;

           ...

           mp = getmntopts(options, mopts, &mntflags, &mntaltflags);

           if (mp == NULL)
                   err(EXIT_FAILURE, "getmntopts");

           ...

           val = getmntoptnum(mp, "rsize");
           freemntopts(mp);


DIAGNOSTICS

     If the external integer variable getmnt_silent is zero then the
     getmntopts(), getmntoptstr(), and getmntoptnum() functions display an
     error message and exit if an error occurred.  By default getmnt_silent is
     zero.


SEE ALSO

     err(3), mount(8)


HISTORY

     The getmntopts() function appeared in 4.4BSD.  It was moved to the utili-
     ties library and enhanced to retrieve option values in NetBSD 2.0.

NetBSD 8.0                        May 4, 2010                       NetBSD 8.0