unix tool for making bootable plan9 disks.
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196
sys/src/cmd/unix/mbrfix.c
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196
sys/src/cmd/unix/mbrfix.c
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdarg.h>
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#include <sys/types.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <string.h>
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typedef unsigned char uchar;
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typedef unsigned int uint;
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typedef unsigned long long vlong;
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enum {
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Sectsz = 0x200,
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Psectsz = 11,
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Pclustsc = 13,
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Presvd = 14,
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Pnumfat = 16,
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Pfatsz = 22,
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Pfatsz32 = 36,
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Pvolid = 67,
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};
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int
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readn(int f, void *av, int n)
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{
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char *a;
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int m, t;
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a = av;
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t = 0;
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while(t < n){
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m = read(f, a+t, n-t);
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if(m <= 0){
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if(t == 0)
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return m;
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break;
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}
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t += m;
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}
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return t;
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}
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void
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sysfatal(char *fmt, ...)
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{
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va_list va;
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va_start(va, fmt);
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vfprintf(stderr, fmt, va);
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va_end(va);
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fprintf(stderr, "\n");
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exit(1);
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}
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void
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readsect(int fd, uint n, void *data)
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{
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loff_t off;
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off = (loff_t) n * Sectsz;
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if(llseek(fd, off, SEEK_SET) != off)
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sysfatal("seek to sector 0x%x failed", n);
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if(readn(fd, data, Sectsz) != Sectsz)
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sysfatal("short read: %m");
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}
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void
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writesect(int fd, uint n, void *data)
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{
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loff_t off;
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off = (loff_t) n * Sectsz;
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if(llseek(fd, off, SEEK_SET) != off)
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sysfatal("seek to sector 0x%x failed", n);
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if(write(fd, data, Sectsz) != Sectsz)
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sysfatal("short write: %m");
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}
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uint
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getulong(uchar *s)
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{
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return s[0] | (s[1] << 8) | (s[2] << 16) | (s[3] << 24);
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}
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void
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putulong(uchar *s, uint n)
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{
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*s++ = n & 0xff;
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*s++ = (n >> 8) & 0xff;
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*s++ = (n >> 16) & 0xff;
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*s++ = (n >> 24) & 0xff;
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}
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uint
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getushort(uchar *s)
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{
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return s[0] | (s[1] << 8);
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}
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int
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checksig(uchar *s)
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{
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return s[0x1fe] == 0x55 && s[0x1ff] == 0xaa;
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}
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void
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fixpbs(uchar *pbs, uchar *pbs9, uint lba)
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{
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uint a;
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uint fatsz, resvd, numfat;
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numfat = pbs[Pnumfat];
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fatsz = getushort(&pbs[Pfatsz]);
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if(fatsz == 0)
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fatsz = getulong(&pbs[Pfatsz32]);
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resvd = getushort(&pbs[Presvd]);
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a = pbs9[1] + 2;
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memcpy(pbs, pbs9, 3);
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memcpy(pbs+a, pbs9+a, Sectsz-a-2);
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a = lba + numfat * fatsz + resvd;
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printf("Xroot=%x\n", a);
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putulong(&pbs[Pvolid], a);
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}
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int
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main(int argc, char *argv[])
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{
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int dev, fd, i;
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uchar mbr9[Sectsz], pbs9[Sectsz];
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uchar mbr[Sectsz], pbs[Sectsz];
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uint lba;
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int part, want;
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char *mbrfn, *pbsfn, *devfn;
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if(argc < 4)
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sysfatal("usage: <device> <mbrfile> <pbsfile> [part]");
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devfn = argv[1];
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mbrfn = argv[2];
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pbsfn = argv[3];
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want = argc >= 5 ? atoi(argv[4]) : -1;
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part = -1;
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dev = open(devfn, O_RDWR);
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if(dev < 0)
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sysfatal("%s: %m", devfn);
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if((fd = open(mbrfn, O_RDONLY)) < 0)
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sysfatal("%s: %m", mbrfn);
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if(readn(fd, mbr9, Sectsz) < 3)
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sysfatal("%s: too short", mbrfn);
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close(fd);
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fd = open(pbsfn, O_RDONLY);
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if(fd < 0)
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sysfatal("%s: %m", pbsfn);
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if(readn(fd, pbs9, Sectsz) < 3)
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sysfatal("%s: too short", pbsfn);
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if(pbs9[0] != 0xeb)
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sysfatal("first byte of pbs not a short jump");
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close(fd);
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readsect(dev, 0, mbr);
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if(!checksig(mbr))
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sysfatal("sector 0 is missing signature");
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for(i=0; i<4; i++){
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if(mbr[0x1be + i*16] == 0x80 && (part == -1 || i == want))
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part = i;
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}
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if(part == -1)
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sysfatal("no bootable partitions found");
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if(want != -1 && part != want)
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sysfatal("partition %d is not bootable", want);
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lba = getulong(&mbr[0x1be + part*16 + 8]);
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if(lba == 0)
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sysfatal("partition %d has zero LBA", part);
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readsect(dev, lba, pbs);
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if(!checksig(pbs))
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sysfatal("partition %d (LBA=0x%x) is missing signaure", part, lba);
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if(getushort(&pbs[Psectsz]) != 512)
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sysfatal("sector size not 512");
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printf("using partition %d, LBA=0x%x\n", part, lba);
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memcpy(mbr, mbr9, 446);
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fixpbs(pbs, pbs9, lba);
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writesect(dev, 0, mbr);
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writesect(dev, lba, pbs);
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close(dev);
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return 0;
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}
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