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().