int
uuidgen(
struct uuid *store
, int count
)
)
system call generates
count
universally unique identifiers (UUIDs) and writes them to the buffer
pointed to by
store
.
The identifiers are generated according to the syntax and semantics of the
DCE version 1 variant of universally unique identifiers.
See below for a more in-depth description of the identifiers.
When no IEEE 802
address is available for the node field, a random multi-cast address is
generated for each invocation of the system call.
According to the algorithm of generating time-based UUIDs, this will also
force a new random clock sequence, thereby increasing the likelihood for
the identifier to be unique.
When multiple identifiers are to be generated, the
uuidgen()
system call will generate a set of identifiers that is dense in such a way
that there is no identifier that is larger than the smallest identifier in the
set and smaller than the largest identifier in the set and that is not already
in the set.
Universally unique identifiers, also known as globally unique identifiers
(GUIDs), have a binary representation of 128-bits.
The grouping and meaning of these bits is described by the following
structure and its description of the fields that follow it:
struct uuid {
uint32_t time_low;
uint16_t time_mid;
uint16_t time_hi_and_version;
uint8_t clock_seq_hi_and_reserved;
uint8_t clock_seq_low;
uint8_t node[_UUID_NODE_LEN];
};
)
system call have variant value 10b.
the variant value is stored in the most significant bits of the field.
The binary representation is sensitive to byte ordering. Any multi-byte field is to be stored in the local or native byte-order and identifiers must be converted when transmitted to hosts that do not agree on the byte-order. The specification does not however document what this means in concrete terms and is otherwise beyond the scope of this system call.
)
system call can fail with:
EFAULT
]
store
could not be written to for any or all identifiers.
EINVAL
]
count
argument is less than 1 or larger than the hard upper limit of 2048.
)
system call is itself not part of the specification.
)
system call first appeared in
FreeBSD5.0
and was subsequently added to
NetBSD2.0.