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    SubjectRe: Of removable devices
    In <200002161445.JAA14399@tsx-prime.MIT.EDU> Theodore Y. Ts'o (tytso@MIT.EDU) wrote:
    TT> From: Francis GALIEGUE <francis@mandrakesoft.com>
    TT> Date: 16 Feb 2000 12:57:17 +0100

    TT> "Khimenko Victor" <khim@sch57.msk.ru> writes:

    TT> First, sorry for yelling earlier. I'm conscious of problems with PC
    TT> floppies. Calling block_fsync() regulary is not even a solution, I'm
    TT> aware of this as well - too much overhead for not so much. But a
    TT> newbie is not as stupid to eject a floppy when he sees the LED is on
    TT> (well, at least I hope so :)

    TT> Right. That was the basic design behind supermount, as I understand
    TT> it. Users have been well programmed that if the LED light is off, it's
    TT> safe to pop the disk out. Because Linux normally has different rules,
    TT> this violates the principal of least surprise.

    TT> So the question is whether it's possible to do something relatively
    TT> painless which allows the right thing to happen under most
    TT> circumstances. A key observation is that the sort of programs you
    TT> expect naive users to use: i.e., cp, office suite software,
    TT> etc. generally tends to open a file for writing, write it out
    TT> completely, and then close the file. So if you can automatically
    TT> dismount the filesystem after the close, and then automatically mount
    TT> the filesystem after something tries to touch the dentry, it works 99.9%
    TT> of the time. Is it perfect? No! Is it better than hoping that users
    TT> will adapt to Linux? Well, that's a religious question, but the
    TT> traditional answers is that users are (a) resistant to change and (b)
    TT> highly stubborn, and so it's better to try to make at least some
    TT> consessions to pre-programmed behaviour.

    TT> By the way, ext2 has a serial number, so it *would* be possible to make
    TT> ext2 check the superblock parameter when it was informed that a media
    TT> change may have happened. So it's not just the FAT filesystem that can
    TT> do this.

    This is all doable as I said from the very beginning but it'll require DEEP
    rework of VFS, not just small changes. It IS usefull (for example for discussed
    here situation where you have big disk with rarely used stuff and want to not
    re-fsck it after crash if in fact disk was not used) but it's also HARD work
    if you want to do it right.




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