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8.8.5: MTIOCVOLINFO

The following comes from ftape's replacement

[/usr/src/ftape-4.04/]include/linux/mtio.h

for the kernel's `mtio.h' header file (see MTSETBLK). Note that mt_blksz is measured in bytes but mt_size and mt_rawsize are measured in kilobytes.

struct mtvolinfo {
        unsigned int mt_volno;   /* vol-number */
        unsigned int mt_blksz;   /* blocksize used when recording */
        unsigned int mt_rawsize; /* raw tape space consumed, in kb */
        unsigned int mt_size;    /* volume size after decompression, in kb */
        unsigned int mt_cmpr:1;  /* this volume has been compressed */
};
#define MTIOCVOLINFO _IOR('m', 8, struct mtvolinfo)

This ioctl queries information about the volume the tape drive is positioned at. The meaning of the components of the structure are:

mt_volno

The number of the current volume.


mt_blksz The block-size the volume was recorded with measured in bytes (see MTSETBLK, see Tape blocks).
mt_rawsize The amount of space the volume occupies on the tape measured in kilobytes
mt_size The real size of the volume after decompression measured in kilobytes
mt_cmpr This indicates whether compression was used to record the volume, See zftape devices. Note that ftape-4.04 no longer supports writing of compressed archives while support for reading compressed archives is kept for compatibility reasons.

When this ioctl is send to the driver when it is located at EOM (end of recorded media, end of data), then mt_rawsize gives the amount of data still usable on the tape. In this case the mt_size component will be set to zero and mt_blksz reflects block size currently used by ftape-3.04d (and later versions).


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