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VENTI-PACKET(2) System Calls Manual VENTI-PACKET(2)
Packet, packetalloc, packetappend, packetasize, packetcmp, packetcon‐
cat, packetconsume, packetcopy, packetdup, packetforeign, packetfrag‐
ments, packetfree, packetheader, packetpeek, packetprefix, packetsha1,
packetsize, packetsplit, packetstats, packettrailer, packettrim - zero-
copy network buffers
void packetappend(Packet *p, uchar *buf, int n)
uint packetasize(Packet *p)
int packetcmp(Packet *p, Packet *q)
void packetconcat(Packet *p, Packet *q)
int packetconsume(Packet *p, uchar *buf, int n)
int packetcopy(Packet *p, uchar *buf, int offset, int n)
Packet* packetdup(Packet *p, int offset, int n)
Packet* packetforeign(uchar *buf, int n,
void (*free)(void *a), void *a)
int packetfragments(Packet *p, IOchunk *io, int nio,
void packetfree(Packet *p)
uchar* packetheader(Packet *p, int n)
uchar* packetpeek(Packet *p, uchar *buf, int offset, int n)
void packetprefix(Packet *p, uchar *buf, int n)
void packetsha1(Packet *p, uchar sha1)
uint packetsize(Packet *p)
Packet* packetsplit(Packet *p, int n)
uchar* packettrailer(Packet *p, int n)
int packettrim(Packet *p, int offset, int n)
A Packet is a chain of blocks of data. Each block, called a fragment,
is contiguous in memory, but the entire packet may not be. This repre‐
sentation helps avoid unnecessary memory copies.
Packetalloc allocates an empty packet.
Packetappend appends the n bytes at buf to the end of p.
Packetasize returns the number of data bytes allocated to p. This may
be larger than the number of bytes stored in p because fragments may
not be filled completely.
Packetcmp compares the data sections of two packets as memcmp (see mem‐
Packetconcat removes all data from q, appending it to p.
Packetconsume removes n bytes from the beginning of p, storing them
Packetcopy copies n bytes at offset in p to buf.
Packetdup creates a new packet initialized with n bytes from offset in
Packetforeign allocates a packet containing `foreign' data: the n bytes
pointed to by buf. Once the bytes are no longer needed, they are freed
by calling free(a).
Packetfragments initializes up to nio of the io structures with point‐
ers to the data in p, starting at offset. It returns the total number
of bytes represented by the returned structures. Packetfragments ini‐
tializes any unused io structures with nil pointer and zero length.
Packetfree frees the packet p.
Packetheader returns a pointer to the first n bytes of p, making them
contiguous in memory if necessary.
Packetpeek returns a pointer to the n bytes at offset in p. If the
requested bytes are already stored contiguously in memory, the returned
pointer points at the internal data storage for p. Otherwise, the
bytes are copied into buf, and packetpeek returns buf.
Packetprefix inserts a copy of the n bytes at buf at the beginning of
Packetsha1 computes the SHA1 hash of the data contained in p.
Packetsize returns the length, in bytes, of the data contained in p.
Packetsplit returns a new packet initialized with n bytes removed from
the beginning of p.
Packetstats prints run-time statistics to standard output.
Packettrailer returns a pointer to the last n bytes of p, making them
contiguous in memory if necessary.
Packettrim deletes all bytes from the packet p except the n bytes at
These functions return errors only when passed invalid inputs, e.g.,
requests for data at negative offsets or beyond the end of a packet.
Functions returning pointers return nil on error; functions returning
integers return -1 on error. Most functions returning integers return
0 on success. The exceptions are packetfragments and packetcmp, whose
return values are described above.
When these functions run out of memory, they print error messages and