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size of directory / file structure is 32 bytes

In this assignment you are going to read floppy disk. You can run ‘mdir’ Unix function to see what output your program should give. FAT-12 MS-DOS file system: floppy disk uses this file system, and that means the following: - each sector has 512 bytes - each entry in FAT table has 12 bits

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size of directory / file structure is 32 bytes

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  1. In this assignment you are going to read floppy disk.You can run ‘mdir’ Unix function to see what output your program should give. FAT-12 MS-DOS file system:floppy disk uses this file system, and that means the following: - each sector has 512 bytes - each entry in FAT table has 12 bits floppy disk layout: Boot sector: contains lots of details, you don’t need it in this assignment.FAT tables: usually floppy disk contains two identical copies of FAT table.You need to use this table in order to read directories content (for all directories except the root directory) – would be explained later.Root directory: contains one entry for all directory/file that is straight under the root directory (their quantity is limited to 224).Data area: sectors with directories / files data.Pay attention that in each of the items above have their constant place on disk.

  2. Structure of the root directory:root directory contains entries for each directory / file that it contains.Entry for directory / file has the following structure:struct directory { char name[8]; /* 0 file name */ char ext[3]; /* 8 file extension */ unsigned char attr; /* 11 attribute byte */ unsigned char Case; /* 12 case of short filename */ unsigned char ctime_ms; /* 13 creation time, milliseconds (?) */ unsigned char ctime[2]; /* 14 creation time */ unsigned char cdate[2]; /* 16 creation date */ unsigned char adate[2]; /* 18 last access date */ unsigned char startHi[2]; /* 20 start cluster, Hi */ unsigned char time[2]; /* 22 time stamp */ unsigned char date[2]; /* 24 date stamp */ unsigned char start[2]; /* 26 starting cluster number */ unsigned char size[4]; /* 28 size of the file */ { For example, in order to read a name of the first directory / file in the root directory, you need to read sector #19 from the floppy disk, and then read the first entry of this sector, and then read first 8 bytes of this entry. Compile and run mardir.c file (with some floppy disk, of course in disk drive).This program prints names (only) of all directories / files of the root directory. size of directory / file structure is 32 bytes

  3. Directory / file attributes:third field of the directory structure is named attr; its size is one character;it contains on / off bits of directory / file attributes:1. READ_ONLY = 0x01 (1b) – if this bit is on, the file is read only2. HIDDEN  = 0x02 (10b) – if this bit is on, the file is hidden3. SYSTEM = 0x04 (100b) – if this bit is on, the file is system file4. VOLUME = 0x08 (1000b) – isn’t important for us 5. DIRECTORY = 0x10 (10000b) – if this bit is on, the file is directory6. ARCHIVE = 0x20 (100000b) - if this bit is on, the file is really file (not directory)7. LONG_NAME = 0xF (1111b) – isn’t important for us  We use this attributes when want to show content of any directory on the floppy directory: we don’t show hidden, system, volume files.In order to verify if some directory / file has some attributes, we use binary operations (see the code file that I wrote in order to understand this better). Note: the file I put does only a little part of the work you have to do.Please read maman 15 instructions carefully and implement all of it.

  4. Deleted files:when you delete file (or directory), it name isn’t removed from the directory file that contained it. Operating system just changes its name, putting 0xe5 character as a first character of the name of the deleted file. So if you read some directory, pay attention at the first character of its name: if it is 0xe5, this means that this file was deleted and you have not to show it. Printing directory that is not the root directory:let’s look at the following example: ls /dir1/dir2 FAT table (starting at sector #1): if you scanned sector 59, and didn’t find an entry for dir2 there, you have to scan next sector of dir1; in order to find it, you have to look at entry 59 of FAT and there you will find the number of the next sector of dir1 for example: root directory You have to read sector #59 from floppy disk, and then scan it for entry of directory with name dir2 …name = dir1…start = 59 You have to read sector #73 from floppy disk, and then scan it for entry of directory with name dir2 59: 73 After you found an entry for dir2, use its ‘stat’ field to find its first sector on the floppy disk, and read it; then scan all its entries and print all the file/ directory names with all the details asked in the maman; then read second sector of dir2 using FAT as I explained above, and so on, till you reach the end of dir2 file (-1 in the last FAT entry that you look at).

  5. How you read floppy disk:since we use Unix, all disk drives are mounted into the single tree, and the path of the floppy disk in this tree is “/dev/fd0”.See the code I put in order to learn how to open this file and to read from it. Sorry for the late publish If you have any questions, just send them to me to my email. Good luck at the exam.

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