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printk: Restore previous console_loglevel when re-enabling logging
When logging to console is disabled from userspace using klogctl() and later re-enabled, console_loglevel gets set to the default log level instead to the previous value. This means that if the kernel was booted with 'quiet', the boot is suddenly no longer quiet after logging to console gets re-enabled. Save the current console_loglevel when logging is disabled and restore to that value. If the log level is set to a specific value while disabled, this is interpreted as an implicit re-enabling of the logging. The problem that prompted this patch is described in: http://lkml.org/lkml/2009/6/28/234 There are two variations possible on the patch below: 1) If klogctl(7) is called while logging is not disabled, then set level to default (partially preserving current functionality): case 7: /* Enable logging to console */ - console_loglevel = default_console_loglevel; + if (saved_console_loglevel == -1) + console_loglevel = default_console_loglevel; + else { + console_loglevel = saved_console_loglevel; + saved_console_loglevel = -1; + } 2) If klogctl(8) is called while logging is disabled, then don't enable logging, but remember the requested value for when logging does get enabled again: case 8: /* Set level of messages printed to console */ [...] - console_loglevel = len; + if (saved_console_loglevel == -1) + console_loglevel = len; + else + saved_console_loglevel = len; Yet another option would be to ignore the request. Signed-off-by: Frans Pop <elendil@planet.nl> Cc: cryptsetup@packages.debian.org Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> LKML-Reference: <200907061331.49930.elendil@planet.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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1 changed files with 10 additions and 1 deletions
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@ -67,6 +67,8 @@ int console_printk[4] = {
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DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
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};
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static int saved_console_loglevel = -1;
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/*
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* Low level drivers may need that to know if they can schedule in
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* their unblank() callback or not. So let's export it.
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@ -378,10 +380,15 @@ int do_syslog(int type, char __user *buf, int len)
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logged_chars = 0;
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break;
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case 6: /* Disable logging to console */
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if (saved_console_loglevel == -1)
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saved_console_loglevel = console_loglevel;
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console_loglevel = minimum_console_loglevel;
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break;
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case 7: /* Enable logging to console */
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console_loglevel = default_console_loglevel;
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if (saved_console_loglevel != -1) {
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console_loglevel = saved_console_loglevel;
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saved_console_loglevel = -1;
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}
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break;
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case 8: /* Set level of messages printed to console */
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error = -EINVAL;
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@ -390,6 +397,8 @@ int do_syslog(int type, char __user *buf, int len)
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if (len < minimum_console_loglevel)
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len = minimum_console_loglevel;
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console_loglevel = len;
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/* Implicitly re-enable logging to console */
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saved_console_loglevel = -1;
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error = 0;
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break;
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case 9: /* Number of chars in the log buffer */
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