Historically the N_TTY driver could never fail but this has become broken over time. Rather than trying to rewrite half the ldisc layer to fix the breakage introduce a second level of fallback with an N_NULL ldisc which cannot fail, and thus restore the guarantees required by the ldisc layer. We still try and fail to N_TTY first. It's much more useful to find yourself back in your old ldisc (first attempt) or in N_TTY (second attempt), and while I'm not aware of any code out there that makes those assumptions it's good to drive(r) defensively.
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| @@ -36,5 +36,6 @@ · 35 unmodified lines | ||
| 36 | 36 | #define N_TRACEROUTER 24 /* Trace data routing for MIPI P1149.7 */ |
| 37 | 37 | #define N_NCI 25 /* NFC NCI UART */ |
| 38 | 38 | #define N_SPEAKUP 26 /* Speakup communication with synths */ |
| 39 | +#define N_NULL 27 /* Null ldisc used for error handling */ | |
| 39 | 40 | |
| 40 | 41 | #endif /* _UAPI_LINUX_TTY_H */ |