ref: ecba7822e316d6cb8370eec97862215402811e82
dir: /sys/man/2/venti-packet/
.TH VENTI-PACKET 2 .SH NAME Packet, packetalloc, packetappend, packetasize, packetcmp, packetconcat, packetconsume, packetcopy, packetdup, packetforeign, packetfragments, packetfree, packetheader, packetpeek, packetprefix, packetsha1, packetsize, packetsplit, packetstats, packettrailer, packettrim \- zero-copy network buffers .SH SYNOPSIS .ft L #include <u.h> .br #include <libc.h> .br #include <venti.h> .ta +\w'\fLPacket* 'u +\w'\fLxxxx'u .PP .B .PP .B Packet* packetalloc(void); .PP .B void packetappend(Packet *p, uchar *buf, int n) .PP .B uint packetasize(Packet *p) .PP .B int packetcmp(Packet *p, Packet *q) .PP .B void packetconcat(Packet *p, Packet *q) .PP .B int packetconsume(Packet *p, uchar *buf, int n) .PP .B int packetcopy(Packet *p, uchar *buf, int offset, int n) .PP .B Packet* packetdup(Packet *p, int offset, int n) .PP .B Packet* packetforeign(uchar *buf, int n, .br .B void (*free)(void *a), void *a) .PP .B int packetfragments(Packet *p, IOchunk *io, int nio, .br .B int offset) .PP .B void packetfree(Packet *p) .PP .B uchar* packetheader(Packet *p, int n) .PP .B uchar* packetpeek(Packet *p, uchar *buf, int offset, int n) .PP .B void packetprefix(Packet *p, uchar *buf, int n) .PP .B void packetsha1(Packet *p, uchar sha1[20]) .PP .B uint packetsize(Packet *p) .PP .B Packet* packetsplit(Packet *p, int n) .PP .B void packetstats(void) .PP .B uchar* packettrailer(Packet *p, int n) .PP .B int packettrim(Packet *p, int offset, int n) .SH DESCRIPTION A .B 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 representation helps avoid unnecessary memory copies. .PP .I Packetalloc allocates an empty packet. .PP .I Packetappend appends the .I n bytes at .I buf to the end of .IR p . .PP .I Packetasize returns the number of data bytes allocated to .IR p . This may be larger than the number of bytes stored in .IR p because fragments may not be filled completely. .PP .I Packetcmp compares the data sections of two packets as .I memcmp (see .IR memory (2)) would. .PP .I Packetconcat removes all data from .IR q , appending it to .IR p . .PP .I Packetconsume removes .I n bytes from the beginning of .IR p , storing them into .IR buf . .PP .I Packetcopy copies .I n bytes at .I offset in .I p to .IR buf . .PP .I Packetdup creates a new packet initialized with .I n bytes from .I offset in .IR p . .PP .I Packetforeign allocates a packet containing `foreign' data: the .I n bytes pointed to by .IR buf . Once the bytes are no longer needed, they are freed by calling .IB free ( a )\fR. .PP .I Packetfragments initializes up to .I nio of the .I io structures with pointers to the data in .IR p , starting at .IR offset . It returns the total number of bytes represented by the returned structures. .I Packetfragments initializes any unused .I io structures with nil pointer and zero length. .PP .I Packetfree frees the packet .IR p . .PP .I Packetheader returns a pointer to the first .I n bytes of .IR p , making them contiguous in memory if necessary. .PP .I Packetpeek returns a pointer to the .I n bytes at .I offset in .IR p . If the requested bytes are already stored contiguously in memory, the returned pointer points at the internal data storage for .IR p . Otherwise, the bytes are copied into .IR buf , and .I packetpeek returns .IR buf . .PP .I Packetprefix inserts a copy of the .I n bytes at .I buf at the beginning of .IR p . .PP .I Packetsha1 computes the SHA1 hash of the data contained in .IR p . .PP .I Packetsize returns the length, in bytes, of the data contained in .IR p . .PP .I Packetsplit returns a new packet initialized with .I n bytes removed from the beginning of .IR p . .PP .I Packetstats prints run-time statistics to standard output. .PP .I Packettrailer returns a pointer to the last .I n bytes of .IR p , making them contiguous in memory if necessary. .PP .I Packettrim deletes all bytes from the packet .I p except the .I n bytes at offset .IR offset . .SH SOURCE .B /sys/src/libventi .SH SEE ALSO .IR venti (2) .SH DIAGNOSTICS These functions return errors only when passed invalid inputs, .IR e.g. , requests for data at negative offsets or beyond the end of a packet. .PP 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 .I packetfragments and .IR packetcmp , whose return values are described above. .PP When these functions run out of memory, they print error messages and call .IR sysfatal .