Principles of Computer Systems
Winter 2021
Stanford University
Computer Science Department
Instructors: Chris Gregg and
Nick Troccoli
Thanks to Ryan Eberhardt for the illustrations and the text used in these slides, and to Ryan and Jerry Cain for the content.
class Drive {
public:
size_t getNumSectors() const;
void readSector(size_t num, unsigned char data[]) const;
void writeSector(size_t num, const unsigned char data[]);
};
Example: the block size could be defined as two sectors
struct inode {
uint16_t i_mode; // bit vector of file
// type and permissions
uint8_t i_nlink; // number of references
// to file
uint8_t i_uid; // owner
uint8_t i_gid; // group of owner
uint8_t i_size0; // most significant byte
// of size
uint16_t i_size1; // lower two bytes of size
// (size is encoded in a
// three-byte number)
uint16_t i_addr[8]; // device addresses
// constituting file
uint16_t i_atime[2]; // access time
uint16_t i_mtime[2]; // modify time
};
7088881/521004/957121/4270046/37984/320459/1008443/5021000/2235666/154718
." 😱 (in reality, you would just say "I put the roster at 154718", but that would not represent any directory hierarchy.
/usr/class/cs110/WWW/index.html
—to seemingly magic numbers that incidentally identify where the corresponding inodes sit in the inode table./usr/class/cs110/staff/master_repos/assign1/amazon.cc
. At 53 characters, the name wouldn't fit in an inode even if the inode stored nothing else./usr/class/cs110/example.txt
. First, we find the inode for the file /
(which always has inumber 1. See here about why it is 1 and not 0). We search inode 1's payload for the token usr
and its companion inumber. Let's say it's at inode 5. Then, we get inode 5's contents (which is another directory) and search for the token class
in the same way. From there, we look up the token cs110
and then example.txt
. This will (finally) be an inode that designates a file, not a directory.rm filename
in Unix) only removes the reference, not the actual file itself.struct inode {
...
uint8_t i_nlink; // number of references
// to file
...
};
Example of hard link creation, deletion, etc.:
cgregg@myth66:/tmp$ clear
cgregg@myth66:/tmp$ echo "This is some text in a file" > file1
cgregg@myth66:/tmp$ ls -l file1
-rw------- 1 cgregg operator 28 Sep 27 09:50 file1
cgregg@myth66:/tmp$ ln file1 file2
cgregg@myth66:/tmp$ ls -l file*
-rw------- 2 cgregg operator 28 Sep 27 09:50 file1
-rw------- 2 cgregg operator 28 Sep 27 09:50 file2
cgregg@myth66:/tmp$ diff file1 file2
cgregg@myth66:/tmp$ echo "Here is some more text." >> file1
cgregg@myth66:/tmp$ cat file1
This is some text in a file
Here is some more text.
cgregg@myth66:/tmp$ cat file2
This is some text in a file
Here is some more text.
cgregg@myth66:/tmp$ ls -l file*
-rw------- 2 cgregg operator 52 Sep 27 09:51 file1
-rw------- 2 cgregg operator 52 Sep 27 09:51 file2
cgregg@myth66:/tmp$ ln file2 file3
cgregg@myth66:/tmp$ ls -l file*
-rw------- 3 cgregg operator 52 Sep 27 09:51 file1
-rw------- 3 cgregg operator 52 Sep 27 09:51 file2
-rw------- 3 cgregg operator 52 Sep 27 09:51 file3
cgregg@myth66:/tmp$ rm file1 file2
rm: remove regular file 'file1'? y
rm: remove regular file 'file2'? y
cgregg@myth66:/tmp$ ls -l file*
-rw------- 1 cgregg operator 52 Sep 27 09:51 file3
cgregg@myth66:/tmp$ cat file3
This is some text in a file
Here is some more text.
cgregg@myth66:/tmp$ rm file3
rm: remove regular file 'file3'? y
cgregg@myth66:/tmp$ ls -l file*
ls: cannot access 'file*': No such file or directory
cgregg@myth66:/tmp$
ln
command.-s
flag with ln
.cgregg@myth66:/tmp$ echo "This is some text in a file" > file1
cgregg@myth66:/tmp$ ls -l file*
-rw------- 1 cgregg operator 28 Sep 27 09:57 file1
cgregg@myth66:/tmp$ ln -s file1 file2
cgregg@myth66:/tmp$ ls -l file*
-rw------- 1 cgregg operator 28 Sep 27 09:57 file1
lrwxrwxrwx 1 cgregg operator 5 Sep 27 09:58 file2 -> file1
cgregg@myth66:/tmp$ echo "Here is some more text." >> file2
cgregg@myth66:/tmp$ cat file1
This is some text in a file
Here is some more text.
cgregg@myth66:/tmp$ rm file1
rm: remove regular file 'file1'? y
cgregg@myth66:/tmp$ ls -l file*
lrwxrwxrwx 1 cgregg operator 5 Sep 27 09:58 file2 -> file1
cgregg@myth66:/tmp$ cat file2
cat: file2: No such file or directory
cgregg@myth66:/tmp$
ls
gives us the path to the original fileWe want to find a file called "/local/files/fairytale.txt", which is a small file.
Steps:
We want to find a file called "/medfile", which is a large-sized file.
Steps:
We want to find a file called "/largefile", which is a very large file.
Steps: