Messages in this thread | | | Subject | Re: Printk mulitple line message support | From | Huang Ying <> | Date | Tue, 15 Nov 2011 09:52:37 +0800 |
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On Tue, 2011-11-15 at 09:18 +0800, Joe Perches wrote: > On Tue, 2011-11-15 at 08:50 +0800, Huang Ying wrote: > > On Mon, 2011-11-14 at 22:40 +0800, Joe Perches wrote: > > > On Mon, 2011-11-14 at 14:58 +0800, Huang Ying wrote: > > > > Hi, > > > > > > > > In most cases, printk only guarantees messages from different printk > > > > calling will not be interleaved between each other. But many printk > > > > users uses multiple line to form a complete message and call printk > > > > for each line. So the following situation is possible for two printk > > > > users running on two CPUs. > > > > > > > > line 1 of message from printk user1 > > > > line 1 of message from printk user2 > > > > line 2 of message from printk user1 > > > > line 2 of message from printk user2 > > > > > > > > This makes kernel log hard to read. One possible solution to this > > > > issue is to give a sequence number (or ID) to each complete message. > > > > So the above lines will be: > > > > > > > > {1}line 1 of message from printk user1 > > > > {2}line 1 of message from printk user2 > > > > {1}line 2 of message from printk user1 > > > > {2}line 2 of message from printk user2 > > > > > > > > Then some simple script can be used to group lines together according > > > > to sequence number in lines. > > > > > > > > What do you think about that? > > > > > > This makes the typical multi-part but non-interleaved > > > output difficult to read. > > > > With a simple script, we can strip out the sequence # easily. > > > > > How about determining if there is interleaving and > > > emitting sequence # only in those cases? > > > > > > Perhaps test the atomic for the last sequence #. > > > > So we will have no sequence # prefix for printk user1's lines if printk > > user 2 comes in the middle? Something as follow? > > > > line 1 of message from printk user1 > > {2}line 1 of message from printk user2 > > line 2 of message from printk user1 > > {2}line 2 of message from printk user2 > > > > This will make it hard for a script to sort the lines. Where should it > > insert lines from printk user2 in the sort result? > > 90+% it's the previous line. > > I believe you are not solving any real problem > with pr_<level>_ml. > > Most all interleaved complete line uses have some > pr_fmt prefix that distinguishes between the sources.
Except dev_<level> and netdev_<level>, it appears that many general pr_<level> do not have the prefix.
> A perhaps larger problem is interleaved partial > lines with pr_cont.
In an interleaved situation, how to determine <level> for pr_cont? Maybe we should avoid use it if we care about interleaving?
> I believe that an initiator/terminator is necessary > for reassembly. Something that could be used > with pr_<level>, dev_<level>, netdev_<level>, et al. > > mp_start(&cookie) > pr_<level>(fmt, ...);
Do not need cookie here?
> pr_mp_cont(&cookie, fmt, ...); > pr_mp_cont(&cookie, fmt "\n", ...); > mp_end(&cookie);
With initiator/terminator the kernel log will be more structural, but that will make kernel log a little harder to read too.
Best Regards, Huang Ying
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