Date: Fri, 22 Jul 2011 13:46:28 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Bruce Evans <brde@optusnet.com.au> Cc: "svn-src-head@FreeBSD.org" <svn-src-head@FreeBSD.org>, "svn-src-all@FreeBSD.org" <svn-src-all@FreeBSD.org>, "src-committers@FreeBSD.org" <src-committers@FreeBSD.org>, Hans Petter Selasky <hselasky@c2i.net> Subject: Re: svn commit: r223989 - head/sys/dev/usb/input Message-ID: <4E295504.2060004@FreeBSD.org> In-Reply-To: <20110720221325.E1436@besplex.bde.org> References: <201107181610.49443.hselasky@c2i.net> <4E26AFF8.8080107@FreeBSD.org> <201107201249.39550.hselasky@c2i.net> <20110720221325.E1436@besplex.bde.org>
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on 20/07/2011 18:32 Bruce Evans said the following: [snip] > The low-level console driver should switch to polling mode to read the > keystrokes. However, its API is broken as designed, so it can only > [tell the driver level to] do this around each poll for a character. > Polling involves polling each possible console in turn, so polling mode > must be left after unsuccessfully polling for a short time so as to > get to the next console. This is now done even if there is only 1 > console. Before the multiple-console changes, polling mode was only > left after _successfully_ polling for as long as necessary to read > a character, so things mostly worked -- the race was only lost if > a character arrives in between polls, and you can't type fast enough > for the time between polls to be significant compared with the time > in polls. [snip] > A non-broken API needs cn_open() and cn_close() functions which would > normally switch the driver in an out of polling mode. Given these > interfaces easy to fix the per-character poll to work as well as before > the multiple console changes, including for multiple active consoles. > Just call cn_open() and cn_close() on every active console around the > whole polling loop. A little more is required to prevent races between > characters, and to avoid the races inherent in the cn_checkc() API. > For multi-char input like that at the mountroot prompt, calling > cn_open() and cn_close() around the loop in gets(9) is adequate. The > functions should be almost no-ops when called nested for things like > this. [snip] Thank you for the great explanation of the issue! I think that your suggestion makes a lot of sense and is the proper approach to fixing this issue. Now we need some sole to actually do the work :-) -- Andriy Gapon
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