9 track tapes and block sizes

[Holm Tiffe]

shadoooo via cctalk wrote:

> Hello,
> I have a question about 9 track tapes and block sizes.
> What I know is that tape is subdivided in files by means of marks, and each
> file is subdivided in blocks of equal size.
> Programs like tar use a specific block size to create files on tape.
> However files can have different block sizes like bootloader file,
> installation dumps and root file system copy on 2.11BSD.
> Now suppose you find and unknown tape you want to preserve: using dd you
> could easily 1:1 copy tape files to hard disk files using a SCSI drive and
> Linux.
> But: how you know which block size is on the tape?
> 
> Thanks
> Andrea

I've sometimes created my own simh .tap to Boottape converter (an later
found out that such a thing exists on the net) to create some boottapes
for my pdp11's using a tandberg 8GB quarter inch drive. It worked
(on Freebsd). I've installed 2.11BSD and on a KA630 Quasijarus Unix,

If you set the blocksize to variable you get back the read byte count
from the read() system call und you have to preserve that information to
the new copied tape (that's what the .tap formats are made for).

I know it is the other way around (.tap->tape) but this is my old q&d
tape write program, you hae made the other half yourselves...

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/ioctl.h>
#include<sys/mtio.h>
#include<fcntl.h>

#define MAXBLOCK 50

extern int errno;

main()
{

FILE * ifp;
FILE * ofp;
unsigned char buf[MAXBLOCK*512];
unsigned char * bufp;
unsigned long foffs=0;
struct  mtop mtio;

int blnum,mark,mt;
unsigned int  blen, tlen;
mark=0;

        if((ifp=fopen("tapefile","r"))==NULL)
                {
                        fprintf(stderr,"Cant open input file\n");
                        exit(-1);
                }
        if(system("mt -f /dev/sa0 blocksize 0")<0)
                {
                        fprintf(stderr,"Can't set variable blocksize on /dev/sa0\n");
                        exit(-1);
                }
        if((mt=open("/dev/sa0", O_CREAT|O_TRUNC|O_WRONLY,0666))<0)
                {
                        fprintf(stderr,"Can't open tape device\n");
                        exit(-1);
                }

blnum=0;

l0:
        while(1)
        {
                if(fread(&blen, sizeof(uint32_t),1,ifp)!=1)
                        {
                                fprintf(stderr,"Can't read blocklen\n");
                                fclose(ifp);
                                close(mt);
                                exit(-1);
                        }
                foffs+=sizeof(uint32_t);
                if(blen==0)
                        {
                                if(mark)
                                {
                                        fprintf(stderr,"EOT detected\n");
                                        fclose(ifp);
                                        mtio.mt_op = MTWEOF;
                                        mtio.mt_count = 2;
                                        if (ioctl(mt, MTIOCTOP, &mtio) < 0)
                                                fprintf(stderr, "MTIOCTOP err: %d\n", errno);
                                        close(mt);
                                        exit(0);
                foffs+=sizeof(uint32_t);
                if(blen==0)
                        {
                                if(mark)
                                {
                                        fprintf(stderr,"EOT detected\n");
                                        fclose(ifp);
                                        mtio.mt_op = MTWEOF;
                                        mtio.mt_count = 2;
                                        if (ioctl(mt, MTIOCTOP, &mtio) < 0)
                                                fprintf(stderr, "MTIOCTOP err: %d\n", errno);
                                        close(mt);
                                        exit(0);
                                }
                                else
                                {
                                        fprintf(stderr,"tapemark detected foffs= %08x\n",
                                        blen,foffs);
                                        mark=1;
                                        mtio.mt_op = MTWEOF;
                                        mtio.mt_count = 1;
                                        if (ioctl(mt, MTIOCTOP, &mtio) <
0)
                                                fprintf(stderr, "MTIOCTOP err: %d\n", errno);
                                goto l0;
                                }
                        }
                        else
                                mark=0;
                fprintf(stderr,"foffs %08x,  blen bl %d = %d:%04x\n",foffs,blnum,blen,blen);
                blnum++;
                blen=blen&0x0fffffff; // erase error flags
        
                if(fread(buf,sizeof(unsigned char),blen,ifp)!=blen)
                        {
                                fprintf(stderr,"Cant read blen %dbytes into buffer\n",blen);
                                fclose(ifp);
                                exit(-1);
                        }
                        if (write(mt, buf, blen) < 0)
                                {
                                        fprintf(stderr,"Cant write blen %d bytes into buffer\n",blen );
                                        fclose(ifp);
                                        close(mt);
                                        exit(1);
                                }

                foffs+=blen;
                if(fread(&tlen, sizeof(uint32_t),1,ifp)!=1)
                        {
                                fprintf(stderr,"Cant read trailing blocklen\n");
                                fclose(ifp);
                                exit(-1);
                        }
                foffs+=sizeof(uint32_t);
                if(blen!=tlen)
                        {
                                fprintf(stderr,"heading blocklen %08x != trailing blocklen %08x\n",
                                                blen,tlen);
                                fclose(ifp);
                                exit(-1);
                        }
                        bzero(buf,MAXBLOCK*512);
        }

}


Regards to Italy,

Holm

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