1 /* Copyright (C) 2003 Russ Cox, Massachusetts Institute of Technology */
2 /* See COPYRIGHT */
3 
4 /*
5  * Generic RPC packet multiplexor.  Inspired by but not derived from
6  * Plan 9 kernel.  Originally developed as part of Tra, later used in
7  * libnventi, and then finally split out into a generic library.
8  */
9 
10 #include <u.h>
11 #include <libc.h>
12 #include <mux.h>
13 
14 static int gettag(Mux*, Muxrpc*);
15 static void puttag(Mux*, Muxrpc*);
16 static void enqueue(Mux*, Muxrpc*);
17 static void dequeue(Mux*, Muxrpc*);
18 
19 void
20 muxinit(Mux *mux)
21 {
22 	memset(&mux->lk, 0, sizeof(Mux)-offsetof(Mux, lk));
23 	mux->tagrend.l = &mux->lk;
24 	mux->rpcfork.l = &mux->lk;
25 	mux->sleep.next = &mux->sleep;
26 	mux->sleep.prev = &mux->sleep;
27 }
28 
29 void*
30 muxrpc(Mux *mux, void *tx)
31 {
32 	int tag;
33 	Muxrpc *r, *r2;
34 	void *p;
35 
36 	/* must malloc because stack could be private */
37 	r = mallocz(sizeof(Muxrpc), 1);
38 	if(r == nil)
39 		return nil;
40 	r->r.l = &mux->lk;
41 
42 	/* assign the tag */
43 	qlock(&mux->lk);
44 	tag = gettag(mux, r);
45 	qunlock(&mux->lk);
46 	if(tag < 0 || mux->settag(mux, tx, tag) < 0 || _muxsend(mux, tx) < 0){
47 		qlock(&mux->lk);
48 		puttag(mux, r);
49 		qunlock(&mux->lk);
50 		return nil;
51 	}
52 
53 	/* add ourselves to sleep queue */
54 	qlock(&mux->lk);
55 	enqueue(mux, r);
56 
57 	/* wait for our packet */
58 	while(mux->muxer && !r->p){
59 		rsleep(&r->r);
60 	}
61 
62 	/* if not done, there's no muxer: start muxing */
63 	if(!r->p){
64 		if(mux->muxer)
65 			abort();
66 		mux->muxer = 1;
67 		while(!r->p){
68 			qunlock(&mux->lk);
69 			p = _muxrecv(mux);
70 			if(p)
71 				tag = mux->gettag(mux, p);
72 			else
73 				tag = ~0;
74 			qlock(&mux->lk);
75 			if(p == nil){	/* eof -- just give up and pass the buck */
76 				dequeue(mux, r);
77 				break;
78 			}
79 			/* hand packet to correct sleeper */
80 			if(tag < 0 || tag >= mux->mwait){
81 				fprint(2, "%s: bad rpc tag %ux\n", argv0, tag);
82 				/* must leak packet! don't know how to free it! */
83 				continue;
84 			}
85 			r2 = mux->wait[tag];
86 			r2->p = p;
87 			dequeue(mux, r2);
88 			rwakeup(&r2->r);
89 		}
90 		mux->muxer = 0;
91 
92 		/* if there is anyone else sleeping, wake them to mux */
93 		if(mux->sleep.next != &mux->sleep)
94 			rwakeup(&mux->sleep.next->r);
95 	}
96 	p = r->p;
97 	puttag(mux, r);
98 	qunlock(&mux->lk);
99 	return p;
100 }
101 
102 static void
103 enqueue(Mux *mux, Muxrpc *r)
104 {
105 	r->next = mux->sleep.next;
106 	r->prev = &mux->sleep;
107 	r->next->prev = r;
108 	r->prev->next = r;
109 }
110 
111 static void
112 dequeue(Mux *mux, Muxrpc *r)
113 {
114 	r->next->prev = r->prev;
115 	r->prev->next = r->next;
116 	r->prev = nil;
117 	r->next = nil;
118 }
119 
120 static int 
121 gettag(Mux *mux, Muxrpc *r)
122 {
123 	int i, mw;
124 	Muxrpc **w;
125 
126 	for(;;){
127 		/* wait for a free tag */
128 		while(mux->nwait == mux->mwait){
129 			if(mux->mwait < mux->maxtag-mux->mintag){
130 				mw = mux->mwait;
131 				if(mw == 0)
132 					mw = 1;
133 				else
134 					mw <<= 1;
135 				w = realloc(mux->wait, mw*sizeof(w[0]));
136 				if(w == nil)
137 					return -1;
138 				memset(w+mux->mwait, 0, (mw-mux->mwait)*sizeof(w[0]));
139 				mux->wait = w;
140 				mux->freetag = mux->mwait;
141 				mux->mwait = mw;
142 				break;
143 			}
144 			rsleep(&mux->tagrend);
145 		}
146 
147 		i=mux->freetag;
148 		if(mux->wait[i] == 0)
149 			goto Found;
150 		for(; i<mux->mwait; i++)
151 			if(mux->wait[i] == 0)
152 				goto Found;
153 		for(i=0; i<mux->freetag; i++)
154 			if(mux->wait[i] == 0)
155 				goto Found;
156 		/* should not fall out of while without free tag */
157 		fprint(2, "libfs: nwait botch\n");
158 		abort();
159 	}
160 
161 Found:
162 	mux->nwait++;
163 	mux->wait[i] = r;
164 	r->tag = i+mux->mintag;
165 	return i;
166 }
167 
168 static void
169 puttag(Mux *mux, Muxrpc *r)
170 {
171 	int i;
172 
173 	i = r->tag - mux->mintag;
174 	assert(mux->wait[i] == r);
175 	mux->wait[i] = nil;
176 	mux->nwait--;
177 	mux->freetag = i;
178 	rwakeup(&mux->tagrend);
179 	free(r);
180 }