NAME

getmntopts — 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() 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() 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.