Hi, While we're talking about "what really should be supported", I have an other idea. I went to a lecture about smartcard filesystems some time ago and it was partly about journalling filesystems. I think they should be implemented in the Hurd.
Now what I mean is not ext3. That is only part of it. The journal of ext3 makes sure that the filesystem itself cannot corrupt (as long as there is no hardware failure.) What I mean is a system that makes sure the database of an application cannot corrupt. This can be done using the same method as ext3 uses at the lower level. Only it is important that the journal and the data are not written in incorrect order. Then the application can be sure that a write operation has either completely succeeded, or completely failed. For that, I think some extra communication between the filesystem driver and the application is required. It could be implemented with "sync" calls, but it would be very inefficient to use them all the time, because three calls would be needed for every operation (one for the journal, one for the data, another one for the journal.) Probably it would be much faster anyway to have an external journal on a different disk. Those are details for now anyway. So to summarise what I mean, a program should: 1 - tell the filesystem it begins a journalled operation 2 - do all kinds of disk access 3 - tell the filesystem it is finished with its journalled operation 4 - get a reply from the filesystem that it worked If the filesystem crashes before 3, no operation has been performed at all to the filesystem (there are likely a lot of unused sectors changed, but they are still unused.) If it crashes after 3, it is unknown if the operation worked, but if it did, then it completed all of it, and if it didn't, then it didn't do any of it. I don't expect the program to continue if the filesystem crashes, but if it does then it might do some recovery if it likes. One thing it knows for sure: its database is not corrupted by the filesystem crash. Please let me know your thoughts. Thanks, Bas Wijnen -- I encourage sending me encrypted e-mail. Please send the central message of e-mails as plain text in the message body, not as HTML and definitely not as MS Word. Please do not use the MS Word format for attachments either. for more information, see http://129.125.47.90/e-mail.html
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