1 #include <u.h>
2 #include <libc.h>
3 #include <bio.h>
4
5 vlong
Bseek(Biobufhdr * bp,vlong offset,int base)6 Bseek(Biobufhdr *bp, vlong offset, int base)
7 {
8 vlong n, d;
9
10 switch(bp->state) {
11 default:
12 fprint(2, "Bseek: unknown state %d\n", bp->state);
13 return Beof;
14
15 case Bracteof:
16 bp->state = Bractive;
17 bp->icount = 0;
18 bp->gbuf = bp->ebuf;
19
20 case Bractive:
21 n = offset;
22 if(base == 1) {
23 n += Boffset(bp);
24 base = 0;
25 }
26
27 /*
28 * try to seek within buffer
29 */
30 if(base == 0) {
31 /*
32 * if d is too large for an int, icount may wrap,
33 * so we need to ensure that icount hasn't wrapped
34 * and points within the buffer's valid data.
35 */
36 d = n - Boffset(bp);
37 bp->icount += d;
38 if(d <= bp->bsize && bp->icount <= 0 &&
39 bp->ebuf - bp->gbuf >= -bp->icount)
40 return n;
41 }
42
43 /*
44 * reset the buffer
45 */
46 n = seek(bp->fid, n, base);
47 bp->icount = 0;
48 bp->gbuf = bp->ebuf;
49 break;
50
51 case Bwactive:
52 Bflush(bp);
53 n = seek(bp->fid, offset, base);
54 break;
55 }
56 bp->offset = n;
57 return n;
58 }
59