FCALL(2)FCALL(2)
NAME
Fcall, convS2M, convD2M, convM2S, convM2D, fcallfmt, dirfmt, dirmodefmt, 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, void *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 number 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 pointers 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 routines.
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 argument, for example, for the
wstat
(see
stat(2))
system call.
It checks that the sizes of all the elements of 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 formatted 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
D
and
dirmodefmt
with format letter
M.
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
intro(2),
9p(2),
stat(2),
intro(5)