naftoli@aecom.UUCP (Robert N. Berlinger) (02/21/85)
If you try to volcopy using a no rewind device, volcopy will skip
over the file created by labelit(1M) and create a second file on the
tape with the proper information. It does this w/o any error message,
since it obviously opens the tape to read in the label, then closes
and reopens to write the data. With a rewind device, the tape would
supposedly reposition itself to the begining of the tape and overwrite
the label. I see no apparent fix, since the System V tape driver does
not have ioctl calls to skip around the tape with.
--
Robert Berlinger
...{philabs,cucard,pegasus,ihnp4,rocky2}!aecom!naftoligwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (02/21/85)
> ... I see no apparent fix, since the System V tape driver does > not have ioctl calls to skip around the tape with. On UNIX System V one does not need ioctls to position the tape. </dev/mt/whatever does a file skip, if non-rewinding device, otherwise rewinds. read() can be used to do a block skip in the rare case that it's needed.
naftoli@aecom.UUCP (Robert N. Berlinger) (02/24/85)
> > ... I see no apparent fix, since the System V tape driver does > > not have ioctl calls to skip around the tape with. > > On UNIX System V one does not need ioctls to position the tape. > </dev/mt/whatever does a file skip, if non-rewinding device, > otherwise rewinds. > read() can be used to do a block skip in the rare case that it's > needed. Although the use of rewind and no-rewind devices helps, there is no way to skip backwards a file or record, which is necessary if you want to do relative positioning rather than absolute which is what is needed in the volcopy case. -- Robert Berlinger ...{philabs,cucard,pegasus,ihnp4,rocky2}!aecom!naftoli