Annotation of wikisrc/projects/project/disk-removal.mdwn, revision 1.2

1.1       jmmv        1: [[!template id=project
                      2: 
                      3: title="Graceful USB disk detach/reattach"
                      4: 
                      5: contact="""
                      6: [tech-kern](mailto:tech-kern@NetBSD.org)
                      7: """
                      8: 
                      9: mentors="""
                     10: [Matthias Drochner](mailto:drochner@NetBSD.org), [David Young](mailto:dyoung@NetBSD.org)
                     11: """
                     12: 
1.2     ! jmmv       13: category="kernel"
        !            14: difficulty="hard"
1.1       jmmv       15: duration="3 months"
                     16: 
                     17: description="""
                     18: Make NetBSD behave gracefully when a "live" USB/FireWire disk drive is accidentally detached and re-attached by, for example, creating a virtual block device that receives block-read/write commands on behalf of the underlying disk driver. This device will delegate reads and writes to the disk driver, but it will keep a list of commands that are "outstanding," that is, reads that the disk driver has not completed, and writes that have not "hit the platter," so to speak. Following disk re-attachment, the virtual block device replays its list of outstanding commands. A correct solution will not replay commands to the wrong disk if the removable was replaced instead of re-attached. Provide a character device for userland to read indications that a disk in use was abruptly detached.
                     19: 
                     20: Open questions: Prior art? Isn't this how the Amiga worked? How will this interact with mount/unmount—is there a use-count on devices? Can you leverage "wedges" in your solution? Does any/most/all removable storage indicate reliably when a block written has actually reached the medium?
                     21: """
                     22: ]]
                     23: 
                     24: [[!tag gsoc]]

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