FCALL(2) FCALL(2)
NAME
fcall, convS2M, convD2M, convM2S, convM2D, getS, fcallconv,
dirconv, dirmodeconv - interface to Plan 9 File protocol
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <fcall.h>
int convS2M(Fcall *f, char *ap)
int convD2M(Dir *d, char *ap)
int convM2S(char *ap, Fcall *f, int n)
int convM2D(char *ap, Dir *d)
char *getS(int fd, char *ap, Fcall *f, long *lp)
int dirconv(void *o, int f1, int f2, int f3, int chr)
int fcallconv(void *o, int f1, int f2, int f3, int chr)
int dirmodeconv(void *o, int f2, int f2, int f3, int chr)
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:
typedef
struct Fcall {
char type;
short fid;
short tag;
union {
struct {
ushort oldtag;/* Tflush */
Qid qid; /* Rattach, Rwalk, Ropen, Rcreate */
};
struct {
char uname[NAMELEN]; /* Tauth, Tattach */
char aname[NAMELEN]; /* Tattach */
char auth[NAMELEN]; /* Tattach */
char chal[8+NAMELEN];/* Tauth, Rauth */
};
struct {
char ename[ERRLEN]; /* Rerror */
};
struct {
long perm; /* Tcreate */
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FCALL(2) FCALL(2)
short newfid; /* Tclone, Tclwalk */
char name[NAMELEN]; /* Twalk, Tclwalk, Tcreate */
char mode; /* Tcreate, Topen */
};
struct {
long offset; /* Tread, Twrite */
long count; /* Tread, Twrite, Rread */
char *data; /* Twrite, Rread */
};
struct {
char stat[DIRLEN]; /* Twstat, Rstat */
};
};
} Fcall;
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 Tnop,
Rnop, Tsession, Rsession, 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 selec-
tively by the message types given in comments.
ConvM2S takes a 9P message at ap of length n, and uses it to
fill in Fcall structure f. If the passed message including
any data for Twrite and Rread messages is formatted prop-
erly, the return value is n; otherwise it is 0. For Twrite
and Tread messages, data is set to a pointer into the argu-
ment message, not a copy.
ConvS2M does the reverse conversion, turning f into a mes-
sage starting at ap. The length of the resulting message is
returned. For Twrite and Rread messages, count bytes start-
ing at data are copied into the message.
The constant MAXMSG is the length of the longest message,
excluding data; MAXFDATA (8192) is the maximum count in a
read or write message. Thus messages are guaranteed to be
shorter than MAXMSG+MAXFDATA bytes long.
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 encod-
ing. ConvD2M does the reverse translation, also returning
the length of the encoding.
GetS reads a message from file descriptor fd into ap and
converts the message using convM2S into the Fcall structure
f. The lp argument must point to a long holding the size of
the ap buffer. It is somewhat resilient to transient read
errors. If convM2S succeeds, its return value is stored in
*lp, and getS returns zero. Otherwise getS returns a string
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FCALL(2) FCALL(2)
identifying the error.
Dirconv, fcallconv, and dirmodeconv are formatting routines,
suitable for fmtinstall (see print(2)). They convert Dir*,
Fcall*, and long values into string representations of the
directory buffer, Fcall buffer, or file mode value.
Fcallconv assumes that dirconv has been installed with for-
mat letter `D'.
SEE ALSO
intro(2), stat(2), intro(5)
DIAGNOSTICS
GetS sets errstr.
BUGS
The offset and directory length fields have 8 bytes in the
protocol, but these routines assume they fit into a long.
ConvS2M should check for counts exceeding MAXFMSG.
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