18 February 2013, 19:05 | #1 |
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FFS, RDB and autobooting questions
Related to my project to create bootable CDs for SCSI-based Amigas, I want to experiment with building CD images which have a patched read-only version of FastFileSystem in the RDB.
The patched FFS always treats the partition as write-protected. That helps because some/most CD drive and SCSI device driver combinations don't report that the partition is write-protected in response to TD_PROTSTATUS commands. The result of that being, with the original FFS if a program tries to write to the disk you get a write error instead of a disk write-protected error. Actually patching FFS to force write-protection is no problem and I can post details of which bytes to patch if anyone's interested. But I have some questions about how well that's likely to work:
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19 February 2013, 13:49 | #2 |
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The key to file systems is the dostype. When loading a file system from RDB the driver checks if the dostype is already present in filesystem.resource. If not, it adds it. If it is already present, the version is checked and if the RDB version is higher than the resoruce version, it is replaced. It shouldn't be replaced if the version is equal, but this depends on the driver, I suppose.
When the partitions are mounted, the file system with the corresponding dostype in filesystem.resource is used. So if your patched FFS is the highest version, it is used for all partitions with this dostype. |
19 February 2013, 13:59 | #3 |
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Thanks. The exact behaviour might depend on the SCSI controller's boot ROM and Kickstart version too.
I think changing the DosType is the only solution which wouldn't cause problems for other really-writeable partitions, which could end up using the patched FFS by mistake. Faking a later FFS version would have the same issues. While it's slightly less elegant, I may just settle for adding a Lock SYS: ON command in the startup-sequence. |
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