STYX(10.2)

NAME

Fcall, convS2M, convD2M, convM2S, convM2D, fcallconv, dirconv − C interface to Inferno File protocol

SYNOPSIS

#include <styx.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)

int dirconv(Fmt*)

int fcallconv(Fmt*)

DESCRIPTION

These routines convert messages in the machine-independent format of the Inferno file protocol, Styx (see section 5 of this manual) to and from a more convenient form, an Fcall structure:

typedef structFcall { char type; short fid; ushort tag; ushort oldtag; /* T-Flush */ Qid qid; /* R-Attach, R-Walk, R-Open, R-Create */ char uname[NAMELEN]; /* T-Attach */ char aname[NAMELEN]; /* T-Attach */ char ename[ERRLEN]; /* R-Error */ long perm; /* T-Create */ short newfid; /* T-Clone */ char name[NAMELEN]; /* T-Walk, T-Create */ char mode; /* T-Create, T-Open */ long offset; /* T-Read, T-Write */ long count; /* T-Read, T-Write, R-Read */ char *data; /* T-Write, R-Read */ char stat[DIRLEN]; /* T-Wstat, R-Stat */ } Fcall;

This structure is defined in <styx.h>. See the other pages in this section of the manual for a full description of Styx messages and their encoding. For all message types, the type field of an Fcall holds one of Tnop, Rnop, Tattach, Rattach, etc. (defined in an enumerated type in <styx.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 buffer ap of length n, and attempts to unpack a complete Styx message to fill in Fcall structure f. To help a caller that is reading and processing Styx messages from an input stream that does not preserve message boundaries, the return value distinguishes three cases:

−If the passed message, including any data for Twrite and Rread messages, forms a complete, properly formatted Styx message, the return value is the number of bytes consumed. It can be less than n when further messages or partial messages remain in ap. For Twrite and Tread messages, f−>data is set to a pointer into the argument message, not a copy.

−If the message in ap is incomplete but valid thus far, the return value is 0; more bytes must be read and added to the buffer to complete the message.

−If the message is invalid, the return value is -1.

ConvS2M does the reverse conversion, turning f into a message starting at ap. The length of the resulting message is returned; it returns -1 if the message type is invalid. For Twrite and Rread messages, f−>count bytes starting at f−>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 sys-stat(2). ConvM2D converts the machine-independent form starting at ap into d and returns the length of the encoding. ConvD2M does the reverse translation, also returning the length of the encoding.

Dirconv and fcallconv are print(10.2) formatting routines. They convert Dir* and Fcall* values into string representations of the directory buffer or Fcall buffer. Fcallconv is installed under format F in the Inferno emulator and kernel.

SOURCE

/include/styx.h

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.

Museum