From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: [PATCH] termios.3: Document line length in canonical mode Date: Wed, 17 Feb 2016 11:09:39 +0100 Message-ID: <56C446E3.2070501@gmail.com> References: <1455542819-29184-1-git-send-email-toddy@debian.org> <56C1EEA6.5080500@gmail.com> <56C3A30D.5010101@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <56C3A30D.5010101-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Hurley , "Dr. Tobias Quathamer" Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Daniel Shahaf List-Id: linux-man@vger.kernel.org Hello Peter On 02/16/2016 11:30 PM, Peter Hurley wrote: > On 02/15/2016 07:28 AM, Michael Kerrisk (man-pages) wrote: >> Hello Tobias, >> >> On 02/15/2016 02:26 PM, Dr. Tobias Quathamer wrote: >>> See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git= /tree/drivers/tty/n_tty.c#n1673 >>> See https://bugs.debian.org/797479 >>> --- >>> man3/termios.3 | 9 +++++++++ >>> 1 file changed, 9 insertions(+) >>> >>> diff --git a/man3/termios.3 b/man3/termios.3 >>> index 7d738d4..3f57607 100644 >>> --- a/man3/termios.3 >>> +++ b/man3/termios.3 >>> @@ -728,11 +728,20 @@ requested fewer bytes than are available in t= he current line of input, >>> then only as many bytes as requested are read, >>> and the remaining characters will be available for a future >>> .BR read (2). >>> +.IP * 2 >>> +The maximum line length is 4096 chars (including the line terminat= ion >>> +char); lines longer than 4096 chars are truncated. After 4095 char= s, >>> +input data is still processed but not stored. Overflow processing >>> +ensures the tty can always receive more input until at least one >>> +line can be read. >>> .PP >>> In noncanonical mode input is available immediately (without >>> the user having to type a line-delimiter character), >>> no input processing is performed, >>> and line editing is disabled. >>> +The read buffer will only accept 4095 chars; this provides the >>> +necessary space for a newline char if the input mode is switched >>> +to canonical. >>> The settings of MIN >>> .RI ( c_cc[VMIN] ) >>> and TIME >> >> Thanks for crafting this. I've applied, and tweaked a little to clar= ify >> some details: >> >> * The maximum line length is 4096 chars (including the termi= nating >> newline character); lines longer than 4096 chars are trun= cated. >> After 4095 characters, input data up (but not including) an= y ter=E2=80=90 >> minating newline is discarded. This ensures that the te= rminal >> can always receive more input until at least one line c= an be >> read. >=20 > Hmm. Neither description is accurate of the observable behavior from = userspace. > For example, it's entirely possible to retrieve > 4096 bytes in non-c= anonical > mode, at least since 3.12 Note that the text I quoted applies just to canonical mode: In canonical mode: [...] * The maximum line length is 4096 chars (including the terminat= =E2=80=90 ing newline character); lines longer than 4096 chars are trun= =E2=80=90 cated. After 4095 characters, input data up (but not includ= =E2=80=90 ing) any terminating newline is discarded. This ensures tha= t the terminal can always receive more input until at least on= e line can be read. So, does that seem okay? > And input processing continues on the input, even past 4096 bytes. > Line editing, ISIG, ECHOxx processing still occurs. Yes, but only in noncanonical mode, right? > > It is true that it is not possible to retrieve > 4096 char line in ca= nonical > mode, and I don't see that ever changing via read() because userspace= may > assume it has received a terminated line in 4096-byte read buffer. Yep. So we all seem to agree. =20 > However, the noncanonical mode input buffer size may change in the ne= ar > future. Can you say some more about that? And what changed in 3.13 with respect to noncanonical mode, by the way? Cheers, Michael --=20 Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html