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8.8.1.19: MTSETDRVBUFFER

C code
struct mtop op = { MTSETDRVBUFFER, COUNT };
result = ioctl(tapefd, MTIOCTOP, &op);

Description

Set the tape drive buffer code to number (SCSI tapes).


Abuse

ftape-3.04d (and later versions) abuses this command to set the number of dma buffers it consumes for its cyclic read/write buffer list.


Notes

ftape needs at least 3 dma buffers to work reasonably well.

The maximum allowed number of dma buffers is determined by the FDC driver modules:

ftape-internal.o

The maximum value is 16 but you might get less due to fragmentation of the physical memory. ftape-internal needs a continuous block of at least 32k aligned at 32k boundary. The return value is -ENOMEM if the driver wasn't able to allocate the desired size. In this case it allocates as much as it can. Keep in mind that kernel memory cannot be swapped out.

The default is 3.


bpck-fdc.o
trakker.o

The maximum and minimum value is 4. The drivers are kept in the memory of the external floppy tape drive, so you don't need to worry too much about memory consumption in this case.


Example

set the number of dma buffers to 10. As each dma buffer has a size of 32kb this results in 320kb of memory being allocated for ftape.

mt -f /dev/nqft0 setdrvbuffer 10

References

see Swapout


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