GETMNTOPTS(3)

GETMNTOPTS(3) | 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 operations 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 subsequent `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 utilities library and enhanced to retrieve option values in NetBSD 2.0.

May 4, 2010 | NetBSD 9.3