linux-kernel - Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly fails when VMIN

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Message-ID: <3319f492-9b1b-d006-e903-7de761a87a53@farjump.io>
Date:	Thu, 5 May 2016 01:27:28 +0200
From:	Julio Guerra <julio@...jump.io>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] drivers/tty: read() on a noncanonical blocking tty randomly
 fails when VMIN > received >= buf

>> 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?

-- 
Julio Guerra