Manual Pages  — FETCH

fetch, fubyte, fuword, fuword16, fuword32, fuword64, fueword, fueword32, fueword64 – fetch data from user-space

SYNOPSIS DESCRIPTION RETURN VALUES SEE ALSO

#include <sys/types.h>

#include <sys/systm.h>

int
fubyte(volatile const void *base);

long
fuword(volatile const void *base);

int
fuword16(volatile const void *base);

int32_t
fuword32(volatile const void *base);

int64_t
fuword64(volatile const void *base);

int
fueword(volatile const void *base, long *val);

int
fueword32(volatile const void *base, int32_t *val);

int
fueword64(volatile const void *base, int64_t *val);

The fetch functions are designed to copy small amounts of data from user-space of the current process. If the user address is naturally aligned, then the operation will be performed atomically. Otherwise it may fail or be performed non-atomically, depending on the platform.

The fetch routines provide the following functionality:

fubyte()
	Fetches a byte of data from the user-space address base. The byte read is zero-extended into the results variable.
fuword()
	Fetches a word of data (long) from the user-space address base.
fuword16()
	Fetches 16 bits of data from the user-space address base. The half-word read is zero-extended into the results variable.
fuword32()
	Fetches 32 bits of data from the user-space address base.
fuword64()
	Fetches 64 bits of data from the user-space address base.
fueword()
	Fetches a word of data (long) from the user-space address base and stores the result in the variable pointed by val.
fueword32()
	Fetches 32 bits of data from the user-space address base and stores the result in the variable pointed by val.
fueword64()
	Fetches 64 bits of data from the user-space address base and stores the result in the variable pointed by val.

The callers of fuword(), fuword32() and fuword64() functions cannot distinguish between -1 read from userspace and function failure.

The fubyte(), fuword(), fuword16(), fuword32(), and fuword64() functions return the data fetched or -1 on failure. The fueword(), fueword32() and fueword64() functions return 0 on success and -1 on failure.