Date: Tue, 09 Jan 2024 13:55:07 +0000 From: bugzilla-noreply@freebsd.org To: standards@FreeBSD.org Subject: [Bug 276220] tty_disc canonical input processing: suprising behavior of the EOF cchar Message-ID: <bug-276220-99@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D276220 Bug ID: 276220 Summary: tty_disc canonical input processing: suprising behavior of the EOF cchar Product: Base System Version: 14.0-RELEASE Hardware: amd64 OS: Any Status: New Severity: Affects Some People Priority: --- Component: standards Assignee: standards@FreeBSD.org Reporter: hym2209268914@gmail.com The naive programmer, having some experience with the tty, and having read = the POSIX 2017 may assume that upon input of the EOF cchar just throws it self = away and flushes the dumb line editor's contents to the read queue. That's not what happens in FreeBSD. If a canonical input processing program, like cat(1), chooses to repeatedly read() with nbyte set to 5 bytes, when t= he user presses 'h' 'e' 'l' 'l' 'o' '^D' successively, the read queue will be 6 bytes as reported by FIONREAD. The first read() will complete as expected, returning 5 and decreasing read queue to 1 byte. but when it finishes echoi= ng the chars and read() again, the ttydisc would throw away the 1 byte in the input queue and immediately return 0! The program would then terminate, muc= h to the surprise of the naive programmer. That is, when program read() the input queue when the sole character there = is an EOF, the kernel would incorrectly return 0 rather than throw it away and wait for input. The EOF or canonical mode should not affect the processing = of the input queue, only the dumb line editor.=20 Normally read() returning 0 in canonical input processing should only happen when user have just pressed EOF/EOL/EOL2 and pressed EOF again. If I stop the program via debugger, hit 'hello^D', switch to -icanon via st= ty -f, then continue the program, this weirdness will not happen. The latest Linux kernel does not have this problem.=20 NetBSD kernel also has this problem. --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-276220-99>