DCMD_FSYS_MAP_OFFSET

QNX SDP8.0Devctl and Ioctl CommandsDeveloper

Map a logical filesystem offset to a physical filesystem or device offset

Synopsis:

#include <sys/dcmd_blk.h>

#define DCMD_FSYS_MAP_OFFSET   __DIOTF(_DCMD_FSYS, 21, union fs_blkmap)

Arguments to devctl():

Argument Value
filedes A file descriptor that you obtained by opening the device.
dcmd DCMD_FSYS_MAP_OFFSET
dev_data_ptr A pointer to a union fs_blkmap
n_bytes sizeof(union fs_blkmap)
dev_info_ptr NULL

Description:

This command maps a logical filesystem offset to a physical filesystem or device offset, depending on the flag specified in the input. It uses a union fs_blkmap for both input and output: 

union fs_blkmap {
        struct {
                off64_t         logical;
                uint32_t        flags;
        } i;
        struct {
                off64_t         physical;
                uint32_t        nbytes;
        } o;
};

Input:

The i (input) member includes:

logical
The logical offset.
flags
One of the following:
  • FS_BMAP_FSYS — map to the filesystem.
  • FS_BMAP_DEVICE — map to the physical device.

Output:

The o (output) member includes:

physical
The starting offset, in bytes.
nbytes
The length of the extent.

Errors:

The devctl() function can return the following, in addition to the error codes listed in its entry in the C Library Reference:

ENXIO
There are no more extents.

See also:

devctl() in the QNX OS C Library Reference

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