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Operating Systems Linux C++ Code to Access Linux Hard Disk Sectors (with a LoopBack Virtual Hard Disk) Post 302491389 by Corona688 on Thursday 27th of January 2011 09:43:40 AM
Old 01-27-2011
Why are you opening and closing the file every time you do something?

This especially becomes useless:
Code:
/**
Seek out a Particular Block In the Disk
Block_SIZE=512bytes
*/
int seekDisk()
{
    cout<<"Seeking the File Disk..."<<endl;
    int fd=open(DISK_NAME, O_RDWR);
	if(lseek(fd, 0L, SEEK_SET) != 0L)
        {
                perror("Couldn't seek");
                close(fd);
                return(1);
        }
    close(fd);
    return 0;
}

...because the seek position gets reset every time you open it anyway. You should open it once and keep using the number it gives you. Your read code would end up looking like int readFromDisk(int fd, char *buffer,int length) { ... } iow exactly like normal read...so you might as well get used to ordinary read call instead.

You should also be doing something more with the number of bytes written and read than just printing it. read() and write() will occasionally surprise you with less than you asked for.
 

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disktab(4)						     Kernel Interfaces Manual							disktab(4)

NAME
disktab - Disk description file SYNOPSIS
#include <sys/disklabel.h> DESCRIPTION
The disktab database describes disk geometries and disk partition characteristics. It is used to initialize the disk label on the disk. The format is patterned after the termcap terminal database. Entries in a disktab file consist of a number of : (colon) separated fields. The first entry for each disk gives the names which are known for the disk, separated by | (vertical bar) characters. The last name given should be a long name fully identifying the disk. The following list indicates the normal values stored for each disk entry: Type Description str Type of disk (for example, removable, win- chester) str Type of controller (for example, SMD, ESDI, floppy) num Number of sectors per track num Number of tracks per cylinder num Total number of cylinders on the disk num Number of sectors per cylinder, nc*nt default num Number of sectors per unit, sc*nc default num Sector size in bytes, DEV_BSIZE default bool Controller supports bad144-style bad sector forwarding num Rotation speed, rpm, default 3600 num Sector skew per track, default 0 num Sector skew per cylinder, default 0 num Headswitch time, usec, default 0 num One-cylinder seek time, usec, default 0 num Sector interleave (n:1), default 1 num Drive-type-dependent parameters num Boot block size, default BBSIZE num Superblock size, default SBSIZE num Block size for partition `a' (bytes) num Block size for partition `d' (bytes) num Block size for partition `e' (bytes) num Block size for partition `f' (bytes) num Block size for partition `g' (bytes) num Block size for partition `h' (bytes) num Fragment size for partition `a' (bytes) num Fragment size for partition `d' (bytes) num Fragment size for partition `e' (bytes) num Fragment size for partition `f' (bytes) num Fragment size for partition `g' (bytes) num Fragment size for partition `h' (bytes) num Offset of partition `a' in sectors num Offset of partition `b' in sectors num Offset of partition `c' in sectors num Offset of partition `d' in sectors num Offset of partition `e' in sectors num Offset of partition `f' in sectors num Offset of partition `g' in sectors num Offset of partition `h' in sectors num Size of partition `a' in sectors num Size of partition `b' in sectors num Size of partition `c' in sectors num Size of partition `d' in sectors num Size of partition `e' in sectors num Size of partition `f' in sectors num Size of partition `g' in sectors num Size of partition `h' in sectors str Partition type of partition `a' (4.2BSD file system, swap, etc.) str Partition type of partition `b' str Partition type of partition `c' str Parti- tion type of partition `d' str Partition type of partition `e' str Partition type of partition `f' str Partition type of partition `g' str Partition type of partition `h' EXAMPLES
The following is an example disktab entry: rz25|RZ25|DEC RZ25 Winchester: :ty=winchester:dt=SCSI:ns#62:nt#9:nc#1492: :oa#0:pa#131072:ba#8192:fa#1024: :ob#131072:pb#262144:bb#8192:fb#1024: :oc#0:pc#832527:bc#8192:fc#1024: :od#393216:pd#146437:bd#8192:fd#1024: :oe#539656:pe#146437:be#8192:fe#1024: :of#686096:pf#146437:bf#8192:ff#1024: :og#393216:pg#439311:bg#8192:fg#1024: :oh#0:ph#0:bh#8192:fh#1024: FILES
/etc/disktab RELATED INFORMATION
Functions: getdiskbyname(3) Files: disklabel(4) Commands: disklabel(8), newfs(8) delim off disktab(4)
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