From mboxrd@z Thu Jan 1 00:00:00 1970 From: lsorense@csclub.uwaterloo.ca (Lennart Sorensen) Subject: Re: fdisk & LBA Date: Fri, 12 Aug 2005 17:11:58 -0400 Message-ID: <20050812211158.GQ6714@csclub.uwaterloo.ca> References: <42FB435E.2070607@effigent.net> <47285.62.1.10.150.1123874953.squirrel@webmail.wired-net.gr> <20050812194531.GL31019@csclub.uwaterloo.ca> <40145.62.1.12.3.1123879702.squirrel@webmail.wired-net.gr> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <40145.62.1.12.3.1123879702.squirrel@webmail.wired-net.gr> Sender: linux-c-programming-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Nanakos Chrysostomos Cc: linux-c-programming@vger.kernel.org On Fri, Aug 12, 2005 at 11:48:22PM +0300, Nanakos Chrysostomos wrote: > Yes,the sector size is 512 bytes,but this is not the beginning of my > fourth partition.Please check the code below,and if you can please test > it.. > > mbr.c > ------ > #include > #include > #include > #include > > > struct mbr { > unsigned char boot_indicator; > unsigned char s_head; > unsigned char s_sector; > unsigned char s_cylinder; > unsigned char f_desc; > unsigned char e_head; > unsigned char e_sector; > unsigned char e_cylinder; > unsigned int rs_sector; > unsigned int n_sectors; > } __attribute__((packed)); > > > > int main() > { > int fd; > struct mbr s; > > > fd= open("/dev/hdb",O_RDONLY); > lseek(fd,0x01ee,SEEK_SET); /* This is the 4rth entry,extended for > me*/ > read(fd,&s,sizeof(struct mbr)); > > printf("Partition Entry 1:\n"); > printf("Boot Indicator: %#x\n",s.boot_indicator); > printf("Starting head %u, cylinder %u, sector > %u.\n",s.s_head,((s.s_sector & > 0xc0)<<2)+s.s_cylinder,s.s_sector&0x3f); > printf("Filesystem descriptor: %#x\n",s.f_desc); > printf("Ending head %u, cylinder %u, sector > %u.\n",s.e_head,((s.e_sector & 0xc0)<<2)+ > s.e_cylinder,s.e_sector&0x3f); > printf("Starting sector: %u\n",s.rs_sector); > printf("Number of sectors in partition: %u\n",s.n_sectors); > > fd= open("/dev/hdb4",O_RDONLY); /* Where is this in hdb,offset??*/ It is wherever the partition entry in sector 0 of hdb says partition 4 starts. Why didn't you just print all the partition table entries above rather than just #1, especially since in this case it is number 4 you care about. Print out the start sector number for partition 4 above and you should find the offset for the extended partition table, in the cases where partition 4 is the extended partition. Seek to that location, read the partition table there. That should contain either just a primary partition, or a primary partition and another extended partition. In case it had another extended partition, repeat until no more extended partitions found. > lseek(fd,446L,SEEK_SET); > read(fd,&s,sizeof(struct mbr)); > > printf("\nPartition Entry 4: Extended partition\n"); > printf("Boot Indicator: %#x\n",s.boot_indicator); > printf("Starting head %u, cylinder %u, sector > %u.\n",s.s_head,((s.s_sector & > 0xc0)<<2)+s.s_cylinder,s.s_sector&0x3f); > printf("Filesystem descriptor: %#x\n",s.f_desc); > printf("Ending head %u, cylinder %u, sector > %u.\n",s.e_head,((s.e_sector & 0xc0)<<2)+ > s.e_cylinder,s.e_sector&0x3f); > printf("Starting sector: %u\n",s.rs_sector); > printf("Number of sectors in partition: %u\n",s.n_sectors); > > return 0; > } Say you had this partition table: start sector number of sectors pri1 1 10 (hda1) pri2 11 20 (hda2) pri3 31 10 (hda3) pri4 41 100 (extended) then at sector 41 you would find another partition table: pri1 42 9 (hda5) pri2 51 90 (extended) Then sector 51 contains a partition table: pri1 52 19 (hda6) pri2 71 70 (extended) Then sector 71 has a partition table: pri1 72 69 (hda7) And no more extended entries, so you are done. C/H/S entries are entirely ignored (or should be) on modern drives. Only start sector and total sectors are relevant as far as I understand things. Len Sorensen