What techniques are employed to lower CPU overhead for I/O operations?

You use a log-based SSD to hold your data.  The SSD has 3 blocks with 10 pages per block.  Each page holds a single character.  The SSD has been used for a while and the current state of the SSD is shown below.  The diagram for the SSD contains the following items: FTL mapping logical pages to physical pages block numberpage number (2 lines)state of each page (valid, Erased, or invalid)data stored at each pagean indicator(+) if a page is currently live (has an entry in the FTL)Current State of SSD: FTL     1:  6   2: 10   5:  2   7:  1         8: 20   9:  4  12: 16  13:  9        15: 12  17: 17  18:  5  29: 13        19: 11  20: 14  21: 15  23:  3        24: 18  25:  0  27:  8  28:  7 Block 0          1          2          Page  0000000000 1111111111 2222222222       0123456789 0123456789 0123456789 State vvvvvvvvvv vvvvvvvvvv vEEEEEEEEE Data  Ih7tj3UYbK 34quFTEPXg H          Live  ++++++++++ +++++++++  +           Operations that the OS may perform are:write(Logical Address, Data) – storing the data at the logical address read(Logical Address) – reading the data from the logical address trim(Logical Address) – deleting the data from the logical address

One danger of hard links is dangling references to files.

In a simplified file system the following operations are implemented:   mkdir() – creates a directory creat() – creates an empty file open(), write(), close() – appends a block to a file link() – creates a hard link to a file unlink() – unlinks a file   The on-disk file system is represented by the following:   inode bitmap inode table (each inode surrounded by square brackets) data bitmap data blocks (each block surrounded by square brackets)   The inode structure contains the type (d – directory, f – regular file), a pointer to a single data block (a), and a reference count (r).  A directory data block contains (filename,inode number) pairs.   The current state of the file system is as follows:   inode bitmap  11111100inodes [d a:0 r:4][d a:1 r:2][f a:-1 r:1][f a:-1 r:2][d a:2 r:2][f a:-1 r:1][][]data bitmap   11100000data [(.,0) (..,0) (g,1) (q,2) (u,3) (x,3) (t,4)][(.,1) (..,0)(c,5)] [(.,4) (..,0)][][][][][]

In the FFS filesystem, the system attempts to spread files within the same directory across different groups.

In data journaling, a transaction consists of a begin block, blocks for all updates to the FS, and an end block.

What single OS operation would result in the state of the SSD changing to the following:   FTL     1:  6   2: 10   5:  2   7:  1         8: 20   9:  4  12: 16  13:  9        15: 21  17: 17  18:  5  29: 13        19: 11  20: 14  21: 15  23:  3        24: 18  25:  0  27:  8  28:  7  Block 0          1          2          Page  0000000000 1111111111 2222222222       0123456789 0123456789 0123456789 State vvvvvvvvvv vvvvvvvvvv vvEEEEEEEE Data  Ih7tj3UYbK 34quFTEPXg Hg         Live  ++++++++++ ++ ++++++  ++         

You see a segment with the following set of writes block 100: [(“.” 0), (“..” 0), (“foo” 1)] block 101: [size=1,ptr=100,type=d] block 102: [size=0,ptr=-,type=f] block 103: [imap: 0->XXX,1->102]    What could be the contents of XXX in the above segment?

Hardware that meets the Popek Goldberg criteria can use the trap-and-emulate model for virtualization.

Assuming we start with no state in memory, and have a LFS with that looks like the following: how many disk I/Os do we need to perform to read the contents of the directory “/”?   block 0: Checkpoint region: imap[0..2] -> 3block 1: [(“.” 0), (“..” 0)] block 2: [size=1,ptr=1,type=d] block 3: [imap: 0->2]