Finding tape block size

Finding tape block size

Post by Root Boy J » Fri, 01 Mar 1991 08:36:37

>Assuming your tape subsystem conforms to long-established UNIX practice,
>if the read() system call specifies a read count less than the actual
>block size when reading the "raw tape" device (which is the usual one),
>you should get an I/O error since data will be lost.

I agree with everything Doug said. However, I would like to add that
while mtio(4) says that an error will be returned, many device drivers
will not return one. The only source (Tahoe) I have available to look
at (Lions is at home) says things like:

 * If we were reading raw tape and the only error was that the
 * record was too long, then we don't consider this an error.

                unknown mode: sane


1. Finding the block size of a file on tape - block.c (0/1)

I found this program to find the block size of a file on tape and I
need to know how to use it.  It reads the whole file telling me:

read #xxxx of yyyyy bytes returned zzzzzz

I assume xxxx is the block number,  yyyyy is the block size and zzzzz
is the number of bytes in the block.  What I dont know is how this
helps me.  yyyyy and zzzzz are the same for every block except the
last one for every block size I use.  If I have the right block size,
should the last Block be padded to equel the block size?  If you have
to tell it the block size, why would you need it to find the block

Greg Koch
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