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fix canon-cups-ufr2 for previously broken printers #79689
The ufr2 driver relies on black-box binaries from Canon, with baked-in FHS assumptions. Previously, a
And so blacker arts were needed. Introduce a wrapper that uses
This has some pros and cons. The cons:
The ufr2 driver relies on black-box binaries from Canon, with baked-in FHS assumptions. Previously, a `LD_PRELOAD` shim has been used to adapt calls to some libc functions and correct the path arguments passed. Unfortunately, this hack doesn't work for all printers; some of the Canon libraries rely on invoking syscalls directly, and can't be mollified with `ld.so` tricks. And so blacker arts were needed. Introduce a wrapper that uses `ptrace` to intercept all syscalls performed by the binary; when a supported syscall is identified, read its path argument from the binary's address space, see if it's a broken FHS path, and if necessary inject a corrected path into the process's address space before allowing the fixed-up syscall to proceed. This has some pros and cons. The cons: - `ptrace` is sometimes restricted (it's allowed under the default NixOS config though) - there's a minor performance penalty (syscalls cost several times as much) - it's crazy (this binary doesn't seem to do any of the things that might break it, though) The pros: - got my D530 working (just in time to print that shipping label...) - it's a general solution; it should work for any printer that uses this driver, and it should work for future versions of the driver
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