FCALL(2)FCALL(2)NAME
Fcall, convS2M, convD2M, convM2S, convM2D, fcallfmt, dirfmt, dirmod‐
efmt, read9pmsg, statcheck, sizeS2M, sizeD2M - interface to Plan 9 File
protocol
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <fcall.h>
uint convS2M(Fcall *f, uchar *ap, uint nap)
uint convD2M(Dir *d, uchar *ap, uint nap)
uint convM2S(uchar *ap, uint nap, Fcall *f)
uint convM2D(uchar *ap, uint nap, Dir *d, char *strs)
int dirfmt(Fmt*)
int fcallfmt(Fmt*)
int dirmodefmt(Fmt*)
int read9pmsg(int fd, uchar *buf, uint nbuf)
int statcheck(uchar *buf, uint nbuf)
uint sizeS2M(Fcall *f)
uint sizeD2M(Dir *d)
DESCRIPTION
These routines convert messages in the machine-independent format of
the Plan 9 file protocol, 9P, to and from a more convenient form, an
Fcall structure:
#define MAXWELEM 16
typedef
struct Fcall
{
uchar type;
u32int fid;
ushort tag;
union {
struct {
u32int msize;/* Tversion, Rversion */
char *version; /* Tversion, Rversion */
};
struct {
ushort oldtag;/* Tflush */
};
struct {
char *ename; /* Rerror */
};
struct {
Qid qid; /* Rattach, Ropen, Rcreate */
u32int iounit;/* Ropen, Rcreate */
};
struct {
Qid aqid; /* Rauth */
};
struct {
u32int afid;/* Tauth, Tattach */
char *uname; /* Tauth, Tattach */
char *aname; /* Tauth, Tattach */
};
struct {
u32int perm;/* Tcreate */
char *name; /* Tcreate */
uchar mode; /* Tcreate, Topen */
};
struct {
u32int newfid;/* Twalk */
ushort nwname;/* Twalk */
char *wname[MAXWELEM]; /* Twalk */
};
struct {
ushort nwqid;/* Rwalk */
Qid wqid[MAXWELEM]; /* Rwalk */
};
struct {
vlong offset; /* Tread, Twrite */
u32int count;/* Tread, Twrite, Rread */
char *data; /* Twrite, Rread */
};
struct {
ushort nstat;/* Twstat, Rstat */
uchar *stat; /* Twstat, Rstat */
};
};
} Fcall;
/* these are implemented as macros */
uchar GBIT8(uchar*)
ushort GBIT16(uchar*)
ulong GBIT32(uchar*)
vlong GBIT64(uchar*)
void PBIT8(uchar*, uchar)
void PBIT16(uchar*, ushort)
void PBIT32(uchar*, ulong)
void PBIT64(uchar*, vlong)
#define BIT8SZ 1
#define BIT16SZ 2
#define BIT32SZ 4
#define BIT64SZ 8
This structure is defined in <fcall.h>. See section 5 for a full
description of 9P messages and their encoding. For all message types,
the type field of an Fcall holds one of Tversion, Rversion, Tattach,
Rattach, etc. (defined in an enumerated type in <fcall.h>). Fid is
used by most messages, and tag is used by all messages. The other
fields are used selectively by the message types given in comments.
ConvM2S takes a 9P message at ap of length nap, and uses it to fill in
Fcall structure f. If the passed message including any data for Twrite
and Rread messages is formatted properly, the return value is the num‐
ber of bytes the message occupied in the buffer ap, which will always
be less than or equal to nap; otherwise it is 0. For Twrite and Tread
messages, data is set to a pointer into the argument message, not a
copy.
ConvS2M does the reverse conversion, turning f into a message starting
at ap. The length of the resulting message is returned. For Twrite
and Rread messages, count bytes starting at data are copied into the
message.
The constant IOHDRSZ is a suitable amount of buffer to reserve for
storing the 9P header; the data portion of a Twrite or Rread will be no
more than the buffer size negotiated in the Tversion/Rversion exchange,
minus IOHDRSZ.
The routine sizeS2M returns the number of bytes required to store the
machine-independent representation of the Fcall structure f, including
its initial 32-bit size field. In other words, it reports the number
of bytes produced by a successful call to convS2M.
Another structure is Dir, used by the routines described in stat(2).
ConvM2D converts the machine-independent form starting at ap into d and
returns the length of the machine-independent encoding. The strings in
the returned Dir structure are stored at successive locations starting
at strs. Usually strs will point to storage immediately after the Dir
itself. It can also be a nil pointer, in which case the string point‐
ers in the returned Dir are all nil; however, the return value still
includes their length.
ConvD2M does the reverse translation, also returning the length of the
encoding. If the buffer is too short, the return value will be BIT16SZ
and the correct size will be returned in the first BIT16SZ bytes. (If
the buffer is less that BIT16SZ, the return value is zero; therefore a
correct test for complete packing of the message is that the return
value is greater than BIT16SZ). The macro GBIT16 can be used to
extract the correct value. The related macros with different sizes
retrieve the corresponding-sized quantities. PBIT16 and its brethren
place values in messages. With the exception of handling short buffers
in convD2M, these macros are not usually needed except by internal rou‐
tines.
Analogous to sizeS2M, sizeD2M returns the number of bytes required to
store the machine-independent representation of the Dir structure d,
including its initial 16-bit size field.
The routine statcheck checks whether the nbuf bytes of buf contain a
validly formatted machine-independent Dir entry suitable as an argu‐
ment, for example, for the wstat (see stat(2)) system call. It checks
that the sizes of all the elements of the the entry sum to exactly
nbuf, which is a simple but effective test of validity. Nbuf and buf
should include the second two-byte (16-bit) length field that precedes
the entry when formatted in a 9P message (see stat(5)); in other words,
nbuf is 2 plus the sum of the sizes of the entry itself. Statcheck
also verifies that the length field has the correct value (that is,
nbuf-2). It returns 0 for a valid entry and -1 for an incorrectly for‐
matted entry.
Dirfmt, fcallfmt, and dirmodefmt are formatting routines, suitable for
fmtinstall(2). They convert Dir*, Fcall*, and long values into string
representations of the directory buffer, Fcall buffer, or file mode
value. Fcallfmt assumes that dirfmt has been installed with format
letter and dirmodefmt with format letter
Read9pmsg calls read(2) multiple times, if necessary, to read an entire
9P message into buf. The return value is 0 for end of file, or -1 for
error; it does not return partial messages.
SOURCE
/sys/src/libc/9sys
SEE ALSOintro(2), 9p(2), stat(2), intro(5)FCALL(2)
