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Groups > linux.kernel > #1394812
| From | Peter Hurley <peter@hurleysoftware.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf |
| Date | 2016-05-05 03:00 +0200 |
| Message-ID | <rvfO2-6ep-5@gated-at.bofh.it> (permalink) |
| References | <rve5A-4JL-15@gated-at.bofh.it> <rve5A-4JL-13@gated-at.bofh.it> <rveoW-4Yr-19@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 05/04/2016 04:27 PM, Julio Guerra wrote: >>> When a tty (here a slave pty) is set in noncanonical input and blocking read modes, a read() randomly blocks when: >>> "VMIN > kernel received >= user buffer size > 0". >>> >>> The standard says that read() should block until VMIN bytes are received [1][2]. Whether this is an implementation defined case not really specified by POSIX or not, it should not behave randomly (otherwise it really should be documented in termios manpage). >> >> This is not a bug. >> >> From the termios(3) man page: >> >> * MIN > 0; TIME == 0: read(2) blocks until the lesser of MIN bytes or the number of bytes requested are avail‐ >> able, and returns the lesser of these two values. >> > > This does not appear in my man... > > Anyway, how do you explain the random behavior then? A long standing bug in this read mode allows the asynchronous input processing thread to race with the read() thread and become confused about how much data remains. I fixed this in 4.6; when I run your test on 4.6, it consistently returns the full user buffer. Regards, Peter Hurley
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Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf Peter Hurley <peter@hurleysoftware.com> - 2016-05-05 01:10 +0200
Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf Julio Guerra <julio@farjump.io> - 2016-05-05 01:30 +0200
Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf Peter Hurley <peter@hurleysoftware.com> - 2016-05-05 03:00 +0200
Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-05-05 12:10 +0200
Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN > received >= buf Peter Hurley <peter@hurleysoftware.com> - 2016-05-05 17:30 +0200
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