Fcall, convS2M, convD2M, convM2S, convM2D, fcallfmt, dirfmt, dirmodefmt,
read9pmsg, statcheck, sizeS2M, sizeD2M – interface to Plan 9 File
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 read9pmsg(int fd, uchar *buf, uint nbuf)
int statcheck(uchar *buf, uint nbuf)
uint sizeS2M(Fcall *f)
uint sizeD2M(Dir *d)
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|
u32int msize; /* Tversion, Rversion */
char *version; /* Tversion, Rversion */
ushort oldtag; /* Tflush */
char *ename; /* Rerror */
Qid qid; /* Rattach, Ropen, Rcreate */
u32int iounit; /* Ropen, Rcreate */
Qid aqid; /* Rauth */
u32int afid; /* Tauth, Tattach */
char *uname; /* Tauth, Tattach */
char *aname; /* Tauth, Tattach */
u32int perm; /* Tcreate */
char *name; /* Tcreate */
uchar mode; /* Tcreate, Topen */
u32int newfid; /* Twalk */
ushort nwname; /* Twalk */
char *wname[MAXWELEM]; /* Twalk */
ushort nwqid; /* Rwalk */
Qid wqid[MAXWELEM]; /* Rwalk */
vlong offset; /* Tread, Twrite */
u32int count; /* Tread, Twrite, Rread */
char *data; /* Twrite, Rread */
ushort nstat; /* Twstat, Rstat */
uchar *stat; /* Twstat, Rstat */
/* these are implemented as macros */
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.
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(3).
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
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(3)) 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(9p)); 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(3). 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(3) 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.