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 	/* if not done, there's no muxer: start muxing */
62 	if(!r->p){
63 		if(mux->muxer)
64 			abort();
65 		mux->muxer = 1;
66 		while(!r->p){
67 			qunlock(&mux->lk);
68 			p = _muxrecv(mux);
69 			if(p)
70 				tag = mux->gettag(mux, p);
71 			else
72 				tag = ~0;
73 			qlock(&mux->lk);
74 			if(p == nil){	/* eof -- just give up and pass the buck */
75 				dequeue(mux, r);
76 				break;
77 			}
78 			/* hand packet to correct sleeper */
79 			if(tag < 0 || tag >= mux->mwait){
80 				fprint(2, "%s: bad rpc tag %ux\n", argv0, tag);
81 				/* must leak packet! don't know how to free it! */
82 				continue;
83 			}
84 			r2 = mux->wait[tag];
85 			r2->p = p;
86 			dequeue(mux, r2);
87 			rwakeup(&r2->r);
88 		}
89 		mux->muxer = 0;
90 
91 		/* if there is anyone else sleeping, wake them to mux */
92 		if(mux->sleep.next != &mux->sleep)
93 			rwakeup(&mux->sleep.next->r);
94 	}
95 	p = r->p;
96 	puttag(mux, r);
97 	qunlock(&mux->lk);
98 	return p;
99 }
100 
101 static void
102 enqueue(Mux *mux, Muxrpc *r)
103 {
104 	r->next = mux->sleep.next;
105 	r->prev = &mux->sleep;
106 	r->next->prev = r;
107 	r->prev->next = r;
108 }
109 
110 static void
111 dequeue(Mux *mux, Muxrpc *r)
112 {
113 	r->next->prev = r->prev;
114 	r->prev->next = r->next;
115 	r->prev = nil;
116 	r->next = nil;
117 }
118 
119 static int 
120 gettag(Mux *mux, Muxrpc *r)
121 {
122 	int i, mw;
123 	Muxrpc **w;
124 
125 	for(;;){
126 		/* wait for a free tag */
127 		while(mux->nwait == mux->mwait){
128 			if(mux->mwait < mux->maxtag-mux->mintag){
129 				mw = mux->mwait;
130 				if(mw == 0)
131 					mw = 1;
132 				else
133 					mw <<= 1;
134 				w = realloc(mux->wait, mw*sizeof(w[0]));
135 				if(w == nil)
136 					return -1;
137 				memset(w+mux->mwait, 0, (mw-mux->mwait)*sizeof(w[0]));
138 				mux->wait = w;
139 				mux->freetag = mux->mwait;
140 				mux->mwait = mw;
141 				break;
142 			}
143 			rsleep(&mux->tagrend);
144 		}
145 
146 		i=mux->freetag;
147 		if(mux->wait[i] == 0)
148 			goto Found;
149 		for(; i<mux->mwait; i++)
150 			if(mux->wait[i] == 0)
151 				goto Found;
152 		for(i=0; i<mux->freetag; i++)
153 			if(mux->wait[i] == 0)
154 				goto Found;
155 		/* should not fall out of while without free tag */
156 		fprint(2, "libfs: nwait botch\n");
157 		abort();
158 	}
159 
160 Found:
161 	mux->nwait++;
162 	mux->wait[i] = r;
163 	r->tag = i+mux->mintag;
164 	return i;
165 }
166 
167 static void
168 puttag(Mux *mux, Muxrpc *r)
169 {
170 	int i;
171 
172 	i = r->tag - mux->mintag;
173 	assert(mux->wait[i] == r);
174 	mux->wait[i] = nil;
175 	mux->nwait--;
176 	mux->freetag = i;
177 	rwakeup(&mux->tagrend);
178 	free(r);
179 }