Package: libncursesw6 Version: 6.4+20231121-1 Severity: normal Dear Maintainer,
urlview 1c-1 whose xterm was killed but which didn't die consumes 100% CPU. The event loop is for(;;) switch(getch()) ... and ignores -1 (https://git.sr.ht/~nabijaczleweli/urlview-ng/tree/1c/item/urlview.c#L576). strace -p: read(0, "", 1) = 0 read(0, "", 1) = 0 read(0, "", 1) = 0 read(0, "", 1) = 0 read(0, "", 1) = 0 read(0, "", 1) = 0 &c. ltrace -p: wgetch(0x55e356e14860, 0, 0, 1) = 0xffffffff wgetch(0x55e356e14860, 0xffffffff, 0, 0xffffffff) = 0xffffffff wgetch(0x55e356e14860, 0, 0, 1) = 0xffffffff wgetch(0x55e356e14860, 0xffffffff, 0, 0xffffffff) = 0xffffffff wgetch(0x55e356e14860, 0, 0, 1) = 0xffffffff wgetch(0x55e356e14860, 0xffffffff, 0, 0xffffffff) = 0xffffffff wgetch(0x55e356e14860, 0, 0, 1) = 0xffffffff wgetch(0x55e356e14860, 0xffffffff, 0, 0xffffffff) = 0xffffffff &c. gdb -p, b ./urlview.c:576: (gdb) cont Continuing. Breakpoint 1, main (argc=<optimized out>, argv=<optimized out>) at ./urlview.c:576 576 int c = getch(); (gdb) n 578 switch(c) { (gdb) p c $1 = -1 (gdb) p *__errno_location() $3 = 5 this is EIO. By resetting *__errno_location() = 0 and letting it rip for a few more loops, I see it continue to be 0, so it just returns 0 but doesn't change errno (I'm assuming changing errno is a side-effect of read(), which completes successfully but emptily here), presumably the EIO is from an earlier refresh to a dead pty. getch(3ncurses) on bookworm and sid says RETURN VALUE All routines return the integer ERR upon failure and an integer value other than ERR (OK in the case of ungetch) upon successful completion. wgetch returns ERR if the window pointer is null, or if its timeout expires without having any data, or if the execution was interrupted by a signal (errno will be set to EINTR). so how precisely you're meant to handle this is unclear to me. The first sentence implies "case ERR: exit(1)", but the second implies "case ERR: if(errno != EINTR) exit(1); break" to me. I set no timeouts so I expect that bit to not apply, but I read this as the EINTR parenthetical applying to both the interruption and timeout cases. Either way, if errno isn't (re)set, then returning ERR isn't really reliable or meaningful i think (lest you "errno=0, getch()" always? which kinda sucks). I see SUSv2 XCURSES say: Upon successful completion getch(), mvgetch(), mvwgetch() and wgetch() return the single-byte character, KEY_ value, or ERR. When in the nodelay mode and no data is available, ERR is returned. which makes it silent on the issue. Reopening its pty fails with EIO, as expected, but consulting stty against urlview in a live xterm I see speed 38400 baud; rows 54; cols 172; line = 0; -brkint -icrnl -imaxbel iutf8 -onlcr -icanon -echo so -icanon min=1 time=0, which is by no means a "nodelay" mode, and it doesn't have a "timeout" set. Naturally, setting min=0 time=1 I reproduce the empty-returning read()s, and the unchanging errno. So to this point, I think this just needs disambiguation to the tune of "having any data (with errno unchanged)". Empty read()s from a hung-up teletype aren't covered by the documentation. Naturally this is an adversarial reading, but it may not be obvious to all readers that these are homologous conditions: "or if the read from returns empty \(em be it due to a timeout expiring with no data or due to a hangup (with errno unchanged)," In a similar vein, I see a lot of references to a "cbreak mode" (sometimes in bold) and a "nocbreak mode" (never in bold). I suppose this is a left-over from old berkeley manuals(?), but that's not a feature of the Linux teletype driver, and according to my notes[1] the CBREAK mode features in [V7, 4.4BSD) exclusively, which isn't really useful to the modern reader, with the 4.4BSD URM being released close to 30 years ago now. The only remnant of this remains in stty(1), but that consistently calls it cbreak/-cbreak mapping it to -icanon/icanon. This makes it even more jarring to a modern reader. Anyway, is this behaviour expected, and is the loop best-served as for(;;) switch(errno=0, getch()) case ERR: if(errno != EINTR) { err = true; break 2; } ? Or is there a better way to drive this? Best, наб [1]: https://lfs.nabijaczleweli.xyz/0012-groff-mdoc-*q-spacing/2022-10-23-stty.1-preprint/a4.pdf pp. 20, 67-68 -- System Information: Debian Release: 12.2 APT prefers stable-updates APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable-debug'), (500, 'stable') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 6.1.0-9-amd64 (SMP w/24 CPU threads; PREEMPT) Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_FIRMWARE_WORKAROUND, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en Shell: /bin/sh linked to /usr/bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages libncursesw6 depends on: ii libc6 2.36-9+deb12u3 ii libtinfo6 6.4+20231121-1 Versions of packages libncursesw6 recommends: ii libgpm2 1.20.7-10+b1 libncursesw6 suggests no packages. -- no debconf information
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