On 07/17/2014 05:14 AM, Petr Mládek wrote: > On Wed 2014-07-16 12:26:58, Alex Elder wrote: >> In devkmsg_read(), a variable "cont" holds a character that's used >> to indicate whether a given log line is a "continuation", that is, >> whether a log record should be merged with the one before or after >> it. If a record should be merged with its successor (but not its >> predecessor) that character is 'c'. And the line following such a >> 'c' log record is normally marked with a '+' to show it is continues >> its predecessor. Any other cases are marked '-', indicating the >> log record stands on its own. >> >> There is an exception. If a log record is marked LOG_PREFIX, it >> indicates that this record represents a new log entry, implicitly >> terminating the predecessor--even if the predecessor would otherwise >> have been continued. So a record marked LOG_PREFIX (that is not >> also marked LOG_CONT) should have '-' for its "cont" variable. >> >> The logic that determines this "continuation" character has a bug >> that gets that exceptional case wrong. >> >> The specific case that produces the wrong result is when all of >> these conditions are non-zero: >> user->prev & LOG_CONT >> msg->flags & LOG_PREFIX >> msg->flags & LOG_CONT >> The bug is that despite the message's LOG_PREFIX flag, the >> "cont" character is getting set to '+' rather than 'c'. >> >> The problem is that the message's LOG_PREFIX flag is getting >> ignored if its LOG_CONT flag is also set. Rearrange the logic >> here to produce the correct result. >> >> The following table concisely defines the problem: >> >> prev | msg | msg ||"cont" >> CONT |PREFIX| CONT || char >> ------+------+------++------ >> clear| clear| clear|| '-' >> clear| clear| set || 'c' >> clear| set | clear|| '-' >> clear| set | set || 'c' >> set | clear| clear|| '+' >> set | set | set || '+' > ^^^ typo, it should be:
I will fix this, and it will show up when I re-post the series. > > set | clear | set || '+' > >> set | set | clear|| '-' >> set | set | set || '+' <-- should be 'c' >> >> Signed-off-by: Alex Elder <[email protected]> >> --- >> kernel/printk/printk.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c >> index 301ade3..9e9cf93 100644 >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -572,7 +572,7 @@ static ssize_t devkmsg_read(struct file *file, char >> __user *buf, >> struct printk_log *msg; >> u64 ts_usec; >> size_t i; >> - char cont = '-'; >> + char cont; >> size_t len; >> ssize_t ret; >> >> @@ -619,11 +619,12 @@ static ssize_t devkmsg_read(struct file *file, char >> __user *buf, >> * better readable output. 'c' in the record flags mark the first >> * fragment of a line, '+' the following. >> */ >> - if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT)) >> - cont = 'c'; >> - else if ((msg->flags & LOG_CONT) || >> - ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))) >> + if (user->prev & LOG_CONT && !(msg->flags & LOG_PREFIX)) >> cont = '+'; >> + else if (msg->flags & LOG_CONT) >> + cont = 'c'; >> + else >> + cont = '-'; > > Makes sense. Prefix should be always on a new line. > > Reviewed-by: Petr Mladek <[email protected]> Yay!!! Thanks. -Alex > > Best Regards, > Petr > >> len = sprintf(user->buf, "%u,%llu,%llu,%c;", >> (msg->facility << 3) | msg->level, >> -- >> 1.9.1 >> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
