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3.5.5 General Purpose Drive Variables

The following general purpose drive variables are available. Depending to their type, these variables can be set to a string (precmd, postcmd) or an integer (all others)

fat_bits

The number of FAT bits. This may be 12 or 16. This is very rarely needed, as it can almost always be deduced from information in the boot sector. On the contrary, describing the number of fat bits may actually be harmful if you get it wrong. You should only use it if mtools gets the auto-detected number of fat bits wrong, or if you want to mformat a disk with a weird number of fat bits.

codepage

Describes the DOS code page used for short filenames. This is a number between 1 and 999. By default, code page 850 is used. The reason for this is because this code page contains most of the characters that are also available in ISO-Latin-1. You may also specify a global code page for all drives by using the global default_codepage parameter (outside of any drive description). This parameters exists starting at version 4.0.0

data_map

Remaps data from image file. This is useful for image files which might need additional zero-filled sectors to be inserted. Such is the case for instance for IBM 3174 floppy images. These images represent floppy disks with fewer sectors on their first cylinder. These missing sectors are not stored in the image, but are still counted in the filesystem layout. The data_map allows to fake these missing sectors for the upper layers of mtools. A data_map is a comma-separated sequence of source type and size. Source type may be zero for zero-filled sectors created by map, skip for data in raw image to be ignored (skipped), and nothing for data to be used as is (copied) from the raw image. Datamap is automatically complemented by an implicit last element of data to be used as is from current offset to end of file. Each size is a number followed by a unit: s for a 512 byte sector, K for Kbytes, M for megabytes, G for gigabytes, and nothing for single bytes.

Example:

data_map=1s,zero31s,28s,skip1s would be a map for use with IBM 3174 floppy images. First sector (1s, boot sector) is used as is. Then follow 31 fake zero-filled sectors (zero31s), then the next 28 sectors from image (28s) are used as is (they contain FAT and root directory), then one sector from image is skipped (skip1s), and finally the rest of image is used as is (implicit)

precmd

Executes the given command before opening the device. On some variants of Solaris, it is necessary to call ’volcheck -v’ before opening a floppy device, in order for the system to notice that there is indeed a disk in the drive. precmd="volcheck -v" in the drive clause establishes the desired behavior.

postcmd

Executes the given command after closing the device. May be useful if mtools shares the image file with some other application, in order to release the image file to that application.

blocksize

This parameter represents a default block size to be always used on this device. All I/O is done with multiples of this block size, independently of the sector size registered in the file system’s boot sector. This is useful for character devices whose sector size is not 512, such as for example CD-ROM drives on Solaris.

Only the file variable is mandatory. The other parameters may be left out. In that case a default value or an auto-detected value is used.


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