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    SubjectRe: Add a norecovery option to ext3/4?
    On Mon, 9 April 2007 12:21:15 -0500, Eric Sandeen wrote:
    > Phillip Susi wrote:
    > >
    > > When the filesystem is told to mount the disk read only, that means it
    > > should not write to it.
    > It means the filesystem should not be writeable when it is mounted.
    > This is not the same as saying that the filesystem itself should do no
    > IO in the course of making that read-only mount available.

    The filesystem has two interfaces. One to the device underneith, one to
    userspace. Read-only should certainly mean that no writes cross the
    userspace interface. Traditionally it has implicitly also meant that
    no writes are crossing the device interface. Whether that was/is an
    explicit requirement - who knows.

    Journaling filesystems have introduced this thing called "journal
    replay". And I have to admit, it makes thing _a lot_ easier to always
    replay the journal, even when being mounted read-only.

    But "it is easier" is a pretty lame excuse.

    > Under all conditions it should be safe to mount a read-only block
    > device, but that is not the same as mounting a filesystem read-only.

    In particular, it is a lame excuse when this claim is true. If the
    block-device is read-only, then journal replay will not work as expected
    and all the "not so easy" work has to be done anyway.

    Did I miss anything? Is it actually easier to mount a read-only device
    with unclean journal than mounting a read-write device and not replay
    the journal?


    Joern's library part 8:
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