Messages in this thread | | | Subject | Re: [PATCH] ttyprintk: Add TTY hangup callback. | From | Samo Pogačnik <> | Date | Sat, 24 Apr 2021 11:57:47 +0200 |
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Dne 24.04.2021 (sob) ob 10:16 +0900 je Tetsuo Handa napisal(a): > On 2021/04/24 4:47, Samo Pogačnik wrote: > > At any point the tpk_buffer is potentially multiplexed/interleaved by parts > > of > > required output of any concurrent user, as buffs are being delivered by the > > scheduled writes. > > As long as one line is printed by one printk() call, CONFIG_PRINTK_CALLER=y is > helpful enough to distinguish multilplexed/interleaved messages. I consider > that > ttyprintk offers additional advantage over printk() for allow buffering one > line > of message from userspace. > > > > > As per user buffers look promising with output formatting, the FDs passing > > between tasks lead to the same single buffer (Greg already mentioned that). > > Those programs which use FD passing know what they are doing. If they still > want > one line of message printed via ttyprintk interface, they must do their > buffering > before trying to write() to ttyprintk's file descriptor. > > Use of per "struct file" buffer gives those programs which does not use > FD passing a guarantee that one line of message from those programs won't be > multilplexed/interleaved (with the aid of CONFIG_PRINTK_CALLER=y). > I consider it an improvement. > > > > > The > > other thing which is important to me is the console redirection to > > ttyprintk, > > which automatically brings all concurrent console users to the single open > > of > > ttyprintk. > > Gathering whole console output into one FD is similar to FD passing; that is > inevitable. But use of per "struct file" buffer allows /dev/ttyprintk users > from outside of "gather whole console output into one FD" case to avoid > multilplexed/interleaved messages. I tried /dev/ttyprintk like > https://lkml.kernel.org/r/be9e80b1-5be1-842e-538e-d69a3995d567@i-love.sakura.ne.jp > . >
I think i understand, what would you like to achieve, however implementation wise there seems to be no reference point available in tty write operation that would relate to its tty open/close operations (i.e. open() and close() provide filp while write() does not - probably for a reason) or is there such a relation available?
On the other hand, my main concern is how to provide a reliable system wide collection of all console output via ttyprintk console redirection, while normal operation of system console is preserved (except its output being detoured via printk and as such logged together with kernel output). Such logging is particularly useful for after-the-fact inspection of system operation.
That being said i am thinking about how to permanently enable this redirection as early as possible (i.e. via kernel command line option). I had a working prototype for that some time ago (never posted). Would anybody like to see such functionality?
best regards, Samo
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