W6D1 & W10D1 & W14D1: Lin Tianchuan

W10D1/io-ltc.md

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+# I/O
+
+1. Polling, Busy waiting
+2. Interrupt driven I/O
+3. DMA
+4. Memory-mapped I/O
+5. I/O software layers
+6. Disk scheduling
+7. X-window system

W14D1/review-ltc.md

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+# Review OS
+
+## History
+
+- 1950s: batch processing
+- 1960s: multiprogramming
+- 1970s: time-sharing
+- 1980s: personal computing
+- 1990s: distributed computing
+
+## Process
+
+1. User/kernel process/thread
+2. Interfaces: fork, exec, wait, exit
+3. Scheduling
+4. States: running, ready, blocked, zombie
+
+## Memory
+
+1. Physical memory
+   Interfaces: kmalloc, alloc_pages, vmalloc
+2. Virtual memory
+  - Page table
+  - Interfaces: mmap, munmap, mprotect, mremap, msync
+  - malloc: dynamic memory allocation
+
+## File system
+
+1. File: sequence of bytes
+   Interfaces: open, read, write, close
+2. VFS

W6D1/filesystem-ltc.md

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+# File System
+
+Lin Tianchuan
+
+Examples
+
+- EXT2 (in Linux)
+  by Rémy Card, 1994
+  (FFS at BSD by McKusick)
+- FAT
+  by Tim Paterson, 1980
+
+Filesystem = {set of files}
+
+Q: Where is file A?
+   Where is file A's block (data) ?
+
+The following notes use the ext2 filesystem as an example.
+
+## Disk layout
+
+![](http://www.science.smith.edu/~nhowe/262/oldlabs/img/ext2.png)
+
+Data Block Bitmap & Inode Bitmap: A bit value of 0 indicates that the block/inode is free, while a value of 1 indicates that the block/inode is being used.
+
+![](http://www.science.smith.edu/~nhowe/262/oldlabs/img/ext2_bitmap.png)
+
+## Inode
+
+![](https://www.science.unitn.it/~fiorella/guidelinux/tlk/img84.gif)
+
+struct ext2.inode (128 B)
+
+- 12 direct blocks: pointers to the physical data blocks
+- indirect blocks: points at a block of pointers to data blocks
+- double indirect: points at a block of pointers to blocks of pointers to data blocks
+- triple indirect: ...
+
+K = blk_size / index_size
+
+Max block num of a inode: 12 + K + K^2 + K^3
+
+## Directory inode
+
+![](http://www.science.smith.edu/~nhowe/262/oldlabs/img/dir_entry.png)
+
+## Locating a file
+
+![](http://www.science.smith.edu/~nhowe/262/oldlabs/img/ext2_locate.png)
+
+## Hard link / Symbolic link
+
+- Hard link: multiple entries in (same or different) directory inode point to the same inode.
+  - Every non-root directory inode contains a hard link `.` to itself and a hard link `..` to its parent directory inode.
+- Symbolic link: different inodes. The "content" of the symlink is the name it points to.