Manual Pages  — GETENV

The freeenv() function is used to release the resources allocated by a previous call to kern_getenv(). The env argument passed to freeenv() is the pointer returned by the earlier call to kern_getenv(). Like free(3), the env argument can be NULL, in which case no action occurs.

The kern_setenv() function inserts or resets the kernel environment variable name to value. If the variable name already exists, its value is replaced. This function can fail if an internal limit on the number of environment variables is exceeded.

The kern_unsetenv() function deletes the kernel environment variable name.

The testenv() function is used to determine if a kernel environment variable exists. It returns a non-zero value if the variable name exists and zero if it does not.

The getenv_int(), getenv_long(), getenv_quad(), getenv_uint(), and getenv_ulong() functions look for a kernel environment variable name and parse it as a signed integer, long integer, signed 64-bit integer, unsigned integer, or an unsigned long integer, respectively. These functions fail and return zero if name does not exist or if any invalid characters are present in its value. On success, these function store the parsed value in the integer variable pointed to by data. If the parsed value overflows the integer type, a truncated value is stored in data and zero is returned. If the value begins with a prefix of "0x" it is interpreted as hexadecimal. If it begins with a prefix of "0" it is interpreted as octal. Otherwise, the value is interpreted as decimal. The value may contain a single character suffix specifying a unit for the value. The interpreted value is multiplied by the unit's magnitude before being returned. The following unit suffixes are supported:

Unit	Magnitude
k	2^10
m	2^20
g	2^30
t	2^40

The getenv_string() function stores a copy of the kernel environment variable name in the buffer described by data and size. If the variable does not exist, zero is returned. If the variable exists, up to size, -, 1 characters of its value are copied to the buffer pointed to by data followed by a null character and a non-zero value is returned.

The getenv_bool() function interprets the value of the kernel environment variable name as a boolean value by performing a case-insensitive comparison against the strings "1", "0", "true", and "false". If the environment variable exists and has a valid boolean value, then that value will be copied to the variable pointed to by data. If the environment variable exists but is not a boolean value, then a warning will be printed to the kernel message buffer. The getenv_is_true() and getenv_is_false() functions are wrappers around getenv_bool() that simplify testing for a desired boolean value.