[f40a309] | 1 | /*
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| 2 | =============================================================================
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| 3 | lseek.c -- position a file to a specified byte location
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| 4 | Version 7 -- 1987-10-28 -- D.N. Lynx Crowe
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| 5 | =============================================================================
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| 6 | */
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| 7 |
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| 8 | #define DEBUGIT 0
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| 9 |
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[6262b5c] | 10 | #include "all.h"
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[f40a309] | 11 |
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[7258c6a] | 12 | extern int16_t _seek(struct fcb *fcp);
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[f40a309] | 13 |
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| 14 | #if DEBUGIT
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| 15 | extern short fsdebug;
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| 16 | #endif
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| 17 |
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[7258c6a] | 18 | int32_t lseek(int16_t fd, int32_t pos, int16_t how)
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[f40a309] | 19 | {
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| 20 | register struct fcb *fp;
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| 21 |
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| 22 | if ((fd < 0) OR (fd > MAXCHAN)) {
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| 23 |
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| 24 | #if DEBUGIT
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| 25 | if (fsdebug)
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| 26 | printf("lseek(%d): bad file index\n", fd);
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| 27 | #endif
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| 28 |
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| 29 | errno = EBADF; /* file number bad */
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| 30 | return(-1L);
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| 31 | }
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| 32 |
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| 33 | if (chantab[fd].c_seek EQ 0) {
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| 34 |
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| 35 | #if DEBUGIT
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| 36 | if (fsdebug)
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| 37 | printf("lseek(%d): device not seekable\n", fd);
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| 38 | #endif
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| 39 |
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| 40 | errno = EINVAL; /* device can't seek */
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| 41 | return(-1L);
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| 42 | }
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| 43 |
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| 44 | fp = chantab[fd].c_arg; /* get fcb pointer from channel table */
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| 45 |
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| 46 | switch (how) { /* dispatch off of seek type */
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| 47 |
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| 48 | case 2: /* relative to end of file */
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| 49 | pos += fp->curlen;
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| 50 | break;
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| 51 |
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| 52 | case 1: /* relative to current position */
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| 53 | pos += fp->offset + (fp->curlsn << FILESHFT);
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| 54 |
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| 55 | case 0: /* relative to start of file */
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| 56 | break;
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| 57 |
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| 58 | default:
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| 59 | errno = EINVAL; /* invalid seek type */
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| 60 | return(-1L);
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| 61 | }
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| 62 | /* |
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| 63 |
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| 64 | */
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| 65 | if (pos < 0) { /* trap seeks before BOF */
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| 66 |
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| 67 | fp->offset = 0;
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| 68 | fp->curlsn = 0;
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| 69 | fp->modefl |= FC_ERR;
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| 70 |
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| 71 | #if DEBUGIT
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| 72 | if (fsdebug)
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| 73 | printf("lseek(%d): seek (%ld) is before BOF\n", fd, pos);
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| 74 | #endif
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| 75 |
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| 76 | errno = EINVAL;
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| 77 | return(-1L);
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| 78 |
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| 79 | } else if (pos > fp->curlen) { /* trap seeks past EOF */
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| 80 |
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| 81 | fp->offset = fp->curlen & (BPSEC -1);
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| 82 | fp->curlsn = fp->curlen >> FILESHFT;
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| 83 | fp->modefl |= FC_ERR;
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| 84 |
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| 85 | #if DEBUGIT
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| 86 | if (fsdebug)
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| 87 | printf("lseek(%d): seek (%ld) is after EOF (%ld)\n",
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| 88 | fd, pos, fp->curlen);
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| 89 | #endif
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| 90 |
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| 91 | errno = EINVAL;
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| 92 | return(-1L);
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| 93 | }
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[7258c6a] | 94 |
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[f40a309] | 95 | fp->offset = pos & ((int32_t)BPSEC - 1); /* calculate sector offset */
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| 96 | fp->curlsn = pos >> FILESHFT; /* calculate logical sector */
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| 97 |
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| 98 | if (_seek(fp) < 0) { /* position to the physical sector */
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| 99 |
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| 100 | fp->modefl |= FC_ERR; /* couldn't seek */
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| 101 | errno = EIO;
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| 102 | return(-1L);
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| 103 | }
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| 104 |
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| 105 | if (pos EQ fp->curlen)
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| 106 | fp->modefl |= FC_EOF;
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| 107 |
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| 108 | #if DEBUGIT
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| 109 | if (fsdebug)
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| 110 | printf("lseek(): pos=%d, curlsn=%ld, curdsn=%ld, offset=%u\n",
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| 111 | pos, fp->curlsn, fp->curdsn, fp->offset);
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| 112 | #endif
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| 113 |
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| 114 | return(pos); /* return current position */
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| 115 | }
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[6262b5c] | 116 |
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| 117 |
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