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NAME

Styxserver - C Styx server library

SYNOPSIS

#define Qroot	0

#define MSGMAX	((((8192+128)*2)+3) & ~3)

extern char Enomem[];	/* out of memory */
extern char Eperm[];		/* permission denied */
extern char Enodev[];	/* no free devices */
extern char Ehungup[];	/* i/o on hungup channel */
extern char Eexist[];		/* file exists */
extern char Enonexist[];	/* file does not exist */
extern char Ebadcmd[];	/* bad command */
extern char Ebadarg[];	/* bad arguments */

typedef uvlong	Path;
typedef struct Styxserver	Styxserver;
typedef struct Styxops Styxops;
typedef struct Styxfile Styxfile;
typedef struct Client Client;

struct Styxserver
{
	Styxops *ops;
	Path qidgen;
	int connfd;
	Client *clients;
	Client *curc;
	Styxfile *root;
	Styxfile **ftab;
	void	*priv;	/* private */
};

struct Client
{
	Styxserver *server;
	Client *next;
	int		fd;
	char	msg[MSGMAX];
	uint		nread;		/* valid bytes in msg (including nc)*/
	int		nc;		/* bytes consumed from front of msg by convM2S */
	char	data[MSGMAX];	/* Tread/Rread data */
	int		state;
	Fid		*fids;
	char		*uname;	/* uid */
	char		*aname;	/* attach name */
	void		*u;
};

struct Styxops
{
	char *(*newclient)(Client *c);
	char *(*freeclient)(Client *c);

	char *(*attach)(char *uname, char *aname);
	char *(*walk)(Qid *qid, char *name);
	char *(*open)(Qid *qid, int mode);
	char *(*create)(Qid *qid, char *name, int perm, int mode);
	char *(*read)(Qid qid, char *buf, ulong *n, vlong offset);
	char *(*write)(Qid qid, char *buf, ulong *n, vlong offset);
	char *(*close)(Qid qid, int mode);
	char *(*remove)(Qid qid);
	char *(*stat)(Qid qid, Dir *d);
	char *(*wstat)(Qid qid, Dir *d);
};

struct Styxfile
{
	Dir	d;
	Styxfile *parent;
	Styxfile *child;
	Styxfile *sibling;
	Styxfile *next;
	int ref;
	int open;
	void	*u;
};

char *styxinit(Styxserver *server, Styxops *ops, char *port, int perm, int needfile);
char *styxwait(Styxserver *server);
char *styxprocess(Styxserver *server);
char *styxend(Styxserver *server);

Client *styxclient(Styxserver *server);

Styxfile *styxaddfile(Styxserver *server, Path pqid, Path qid, char *name,
					int mode, char *owner);
Styxfile *styxadddir(Styxserver *server, Path pqid, Path qid, char *name,
					int mode, char *owner);
int styxrmfile(Styxserver *server, Path qid);
Styxfile *styxfindfile(Styxserver *server, Path qid);

int	styxperm(Styxfile *file, char *uid, int mode);
long styxreadstr(ulong off, char *buf, ulong n, char *str);
Qid styxqid(int path, int isdir);
void *styxmalloc(int bytes);
void styxfree(void *p);
void styxdebug(void);

DESCRIPTION

The C Styx server library provides a small suite of functions to enable the production of a file server based on the Inferno Styx protocol. The following elements define the primary routines in the interface:

styxinit(server,ops,port,perm,needfile)
Initializes the interface given a pointer to a Styxserver structure server , a callback table of operations ops , a port number port to announce the file service on and the permissions perm on the root directory. The default permission is 0555 (read and execute for user, group and others) if the latter is specified as -1. If the last argument needfile is set to true, the styx library will check that each path number it deals with has a corresponding file associated with it and, if it hasn't, it will issue a "file does not exist" message automatically. In case of an error, the error message is returned, otherwise nil is returned to indicate success.
styxwait(server)
Waits for communication from a client. Return value as above.
styxprocess(server)
Processes the client message after a successful call to styxwait . This may result in calls to the functions in the table provided to styxinit . Return value as above.
styxend(server)
End all file service. Return value as above.
styxclient(server)
Returns the client whose request is currently being processed.

The next set of functions allow the creation of a file system structure based upon the Styxfile structure. This contains a Dir structure d describing the properties of the file (defined in lib9.h) and pointers to other files in the file tree: parent , child , sibling and next . The ref field counts current references to the file. The open field counts the current number of opens on the file. Finally the u field allows further fields to be tagged onto each file. It is not used by the Styx server library.

Each file must have a unique path number in the server. The root of the tree Qroot always has path number zero. It's corresponding file is created during library initialization and placed in the root field of the server structure. All other files must be supplied with a path number to identify them. Files are created/deleted as follows:


styxaddfile(server,ppath,path,name,mode,owner)
Add a new file (ie non-directory) with the given path path , name name , mode mode and owner owner to the directory identified by the path ppath . If path is -1 the library will generate a unique path number instead. Returns nil if the parent file with path ppath does not exist, if the parent is not a directory, if the path number path already is assigned to a file or if the parent already contains a file of name name .
styxadddir(server,ppath,path,name,mode,owner)
Add a new directory with the given path path , name name , mode mode and owner owner to the directory identified by the path ppath . Returns nil in the same circumstances as styxaddfile .
styxrmfile(server,path)
Remove the file or directory with path path from the file server tree. If the file is a directory, it's contents will be recursively removed. If the file does not exist, -1 is returned, otherwise 0 is returned for success.
styxfindfile(server,path)
Return the file structure corresponding to the file or directory with path path . Nil is returned if the file does not exist.

If the file system is created in this way the Styx library will check read/write/execute permissions, check for invalid uses of files and check that path numbers exist in the file system (see styxinit for the latter). If it's not feasible to do this (for instance if there is a more suitable way of describing the file system in question), then all file checking must be done as part of the callback functions below.

The library provides a callback mechanism so that the implementer of the file server can take corresponding action when a particular request is made of the server. All of these functions may return an error message which will be communicated back to the client. Otherwise they should return nil to indicate the success of the operation. Any of these functions may be nil in which case the library performs a default operation which will be described below. These routines use the Qid structure defined in lib9.h to describe files. This structure contains the path number( path ), a version number( vers ) typically zero and a type( type ) which indicates whether the file is a directory, append-only etc.


newclient(c)
Called whenever a new client connects to the server. The Client structure c contains mainly private data but the uname field contains a user name and the aname field an attach name if required. The u field may be used to tag further data onto each client. It is not used by the Styx server library.
freeclient(c)
Called whenever a client disconnects from the server.
attach(uname,aname)
Called when a client user first mounts the file server. The uname is the user id and aname is typically the file tree to access if the server provides a choice. The default action is to allow the attach to the root of the file system.
walk(qid,name)
In a directory represented by qid , find a file member whose name is that given and place it's Qid in qid . The default action is to perform the walk using any directory structure provided.
open(qid,mode)
Open the file represented by qid with mode mode . The latter may be one of OREAD, OWRITE, ORDWR etc (see lib9.h). If the Qid of the newly opened file is different from that given (a file server may understand the opening of a file called "new" say to signify the creation of a directory whose Qid is returned instead) place it's Qid in qid . The default action is to nominally allow the open.
create(qid,name,perm,mode)
Create a file in the directory given by qid with name name , permissions perm and mode mode . Place the Qid of the newly created file in qid . The default action is to issue a permission denied message.
read(qid,buf,n,offset)
Read n bytes of the file represented by qid at offset offset and place the result in buf. Place in n the actual number of bytes read. The default action is to read directories but to issue permission denied on ordinary files.
write(qid,buf,n,offset)
Write n bytes to the file represented by qid at offset offset from the buffer buf. Place in n the actual number of bytes written. The default action is to issue permission denied.
close(qid,mode)
Close the file represented by qid . The mode it was originally opened with is given by mode . The default action is to allow the close.
remove(qid)
Remove the file represented by qid . The default action is to issue a permission denied message.
stat(qid,d)
Place the information for the file represented by qid in the Dir structure(see lib9.h) d . The default action is to allow the stat using any information in the file tree.
wstat(qid,d)
Update the information for the file represented by qid according to the Dir structure d . The default action is to disallow this with a permission denied message.

A small number of utility functions are provided:


styxperm(file,uid,mode)
Does the file/directory file allow the user uid the permission given by mode . For example use OREAD for read permission, OWRITE for write permission and ORDWR for both.
styxreadstr(off,buf,n,str)
Read n bytes of data from the string str at offset off and place the result in buf . Returns the actual number of bytes read.
styxqid(path,isdir)
Returns a typical Qid structure with the given path number path and whether the Qid is for a directory isdir .
styxmalloc(n)
Allocate n bytes of memory and return it.
styxfree(p)
Free the memory pointed to by p .
styxdebug()
Print out some of the actions of the server.

EXAMPLE

A very small file server example is illustrated. First the include files and globals. 

	#include <lib9.h>
	#include "styxserver.h"

	int nq;
	Styxserver *server;

The main processing loop: 

	main(int argc, char **argv)
	{
		Styxserver s;

		server = &s;
		styxinit(&s, &ops, "6701", 100, 0555, 0);
		myinit(&s);
		for(;;) {
			styxwait(&s);
			styxprocess(&s);
		}
		return 0;
	}

Here the port number is 6701 and the root file permissions are 0555 - no write permission for anyone which implies that files and directories cannot be created in the root directory.

The creation of the directory tree: 

	myinit(Styxserver *s)
	{
		styxaddfile(s, Qroot, 1, "fred", 0664, "inferno");
		styxaddfile(s, Qroot, 2, "joe", 0664, "inferno");
		styxadddir(s, Qroot, 3, "adir", 0775, "inferno");
		styxaddfile(s, 3, 4, "bill", 0664, "inferno");
		styxadddir(s, Qroot, 5, "new", 0775, "inferno");
		styxadddir(s, 5, 6, "cdir", 0775, "inferno");
		styxaddfile(s, 6, 7, "cfile", 0664, "inferno");
		nq = 8;
	}

This creates two files fred and joe and two directories adir and new at the top level. adir contains a file called bill and new contains a directory called cdir which contains a file called cfile . Note that each new path number is unique.

The callback functions: 

	Styxops ops = {
		nil,			/* newclient */
		nil,			/* freeclient */

		nil,			/* attach */
		nil,			/* walk */
		nil,			/* open */
		mycreate,		/* create */
		myread,		/* read */
		nil,			/* write */
		nil,			/* close */
		myremove,	/* remove */
		nil,			/* stat */
		nil,			/* wstat */
	};

Here we choose the defaults most of the time.

The supplied callback routines: 

	char *
	mycreate(Qid *qid, char *name, int perm, int mode)
	{
		int isdir;
		Styxfile *f;

		isdir = perm&DMDIR;
		if(isdir)
			f = styxadddir(server, qid->path, nq++, name , perm, "inferno");
		else
			f = styxaddfile(server, qid->path, nq++, name, perm, "inferno");
		if(f == nil)
			return Eexist;
		*qid = f->d.qid;
		return nil;
	}

	char *
	myremove(Qid qid)
	{
		Styxfile *f;

		f = styxfindfile(server, qid.path);
		if(f != nil && (f->d.qid.type&QTDIR) && f->child != nil)
			return "directory not empty";

		if(styxrmfile(server, qid.path) < 0)
			return Enonexist;
		return nil;
	}

	char *
	myread(Qid qid, char *d, ulong *n, vlong offset)
	{
		if(qid.path != 1){
			*n = 0;
			return nil;
		}
		*n = styxreadstr(offset, d, *n, "abcdeghijklmn");
		return nil;
	}

Permission checking for walk (need execute permission on directory), open (the given mode must be compatible with the file permissions), create and remove (both of which need write permission on directory) is done automatically whenever possible. The functions mycreate and myremove below therefore can omit these checks.

The function mycreate simply creates a directory or file and if the file cannot be added to the directory tree it returns a 'file exists' error string. It sets the Qid for the newly created file before returning.

The function myremove first checks to see if the file represents a non-empty directory, in which case it disallows it's removal. Otherwise it removes the file if it can find it and returns a 'file does not exist' error string if it can't.

The function myread considers all files to be empty except for fred which notionally contains abcdefghijklmn . Note that the number of bytes read is returned in the argument n .

Once this file server is running, the root can be accessed by doing for example 

	mount -A tcp!<address>!6701 /n/remote

under Inferno. Here <address> is the address of the machine running the file server (or the loopback address 127.0.0.1 if it's all on one machine). The -A option is used to prevent authentication which is not supported at the moment. Then we can do 

	cd /n/remote
	ls
	adir
	fred
	joe
	new
	...

For a more complicated file server see /tools/styxtest/styxtest.c.

The file /tools/styxtest/mkfile shows how to compile and link the file server sources.

SOURCE

/Nt/386/include/lib9.h
/tools/libstyx/styxserver.h
/tools/libstyx/styxserver.c
/tools/styxtest/styxtest.c
/tools/styxtest/styxtest0.c

BUGS

Currently the library is available under Windows, Linux and Solaris only.
Authentication is not supported.

STYXSERVER(10.2) Rev:  Tue Jan 29 13:11:34 GMT 2008
original page
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