| Message ID | 1405606151-19875-3-git-send-email-elder@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Thu 2014-07-17 09:09:07, Alex Elder wrote: > Two log record flags--LOG_CONT and LOG_NEWLINE--are mutually > exclusive. That is, one or the other is always set, but they are > never both set at the same time in a log record flags field. What > follows is a great deal of explanation that aims to prove this > assertion. > > Having that knowledge allows us to simplify a bit of logic, and with > a little more work (in follow-on patches) it allows us to do without > some flag values, considerably simplifying things. > > > Log record flags are held in the "cont" continuation buffer, as well > as in "syslog_prev" and "console_prev". Those are discussed later. > > Other than that, log record flags are only set in log_store(): > msg->flags = flags & 0x1f; > There are 5 places log_store() is called: twice from cont_flush(); > and three times from vprintk_emit(). > > Only two single-flag values are ever passed to cont_flush(): > LOG_CONT; and LOG_NEWLINE. That passed-in value is provided to > log_store() either as-is, or modified to include LOG_NOCONS. There > are thus four possible flag combinations supplied to log_store() by > cont_flush(): LOG_CONT; LOG_NEWLINE; LOG_CONT|LOG_NOCONS; or > LOG_NEWLINE|LOG_NOCONS. > > The first call vprintk_emit() makes to log_store() passes a flags > value of LOG_PREFIX|LOG_NEWLINE. The second and third calls pass a > locally-computed "lflags" value, possibly with LOG_CONT added. The > only possible flag combinations held in "lflags" are: 0; > LOG_NEWLINE; LOG_PREFIX; or LOG_NEWLINE|LOG_PREFIX. If LOG_NEWLINE > is not set, LOG_CONT flag is added in the call to log_store(). So > there are four possible flag combinations supplied by cont_flush(): > LOG_CONT; LOG_NEWLINE; LOG_PREFIX|LOG_CONT; or LOG_PREFIX|LOG_NEWLINE. > > Therefore log_store() is never provided (so never records) a flag > value that contains both LOG_CONT and LOG_NEWLINE, and one of those > flags is always present. > > > Meanwhile, the "cont" flags field is only ever assigned value 0, or > a value passed to cont_flush(). The value of cont.flags is only > ever *used* if cont.flushed is true, and that only gets set after > the cont.flags field is assigned to the value passed to > cont_flush(). As mentioned above, cont_flush() is never provided > more than one flag value, and it's always either LOG_NEWLINE > or LOG_CONT. Therefore, for all intents and purposes, cont.flags > only ever holds LOG_NEWLINE or LOG_CONT. > > The only values assigned to "syslog_prev" and "console_prev" are the > initial value LOG_NEWLINE or the flags value from a log record. So > none of these ever hold LOG_CONT and LOG_NEWLINE at the same time. > > This proves that at LOG_CONT and LOG_NEWLINE are in fact mutually > exclusive flags. > > This patch makes the following changes: > - Changes two spots in msg_print_txt() so they no longer bother > checking for LOG_NEWLINE once its known that LOG_CONT is set. > - Changes two |= assignments in vprintk_emit() to be simple > assignments instead, because the result is known to be the > same and it makes it obvious no other flags are involved. > - Assigns LOG_CONT to "lflags" in vprintk_emit() if it does not > contain LOG_NEWLINE (rather than just adding it at the time > of the call to log_store()). > - Adds a short explanatory comment. > - Explicitly pass NULL rather than "dict" (and 0 as its length) > to log_store() in one spot in vprintk_emit(), because we know > the value of dict at that point is always NULL. > > Signed-off-by: Alex Elder <elder@linaro.org> > --- > kernel/printk/printk.c | 23 +++++++++++++---------- > 1 file changed, 13 insertions(+), 10 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index ff1c7ad..1ee1862 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -1006,11 +1006,9 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev, > prefix = false; > > if (msg->flags & LOG_CONT) { > - if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE)) > + if (prev & LOG_CONT) > prefix = false; > - > - if (!(msg->flags & LOG_NEWLINE)) > - newline = false; > + newline = false; > } > > do { > @@ -1639,10 +1637,16 @@ asmlinkage int vprintk_emit(int facility, int level, > text_len += vscnprintf(text + text_len, > sizeof(textbuf) - text_len, fmt, args); > > - /* mark and strip a trailing newline */ > + /* > + * If there's a trailing newline, flag it and strip it off. > + * Otherwise we assume this is a partial log message, to be > + * continued with the next call. > + */ > if (text_len && text[text_len-1] == '\n') { > text_len--; > - lflags |= LOG_NEWLINE; > + lflags = LOG_NEWLINE; > + } else { > + lflags = LOG_CONT; > } > > /* strip kernel syslog prefix and extract log level or control flags */ > @@ -1672,7 +1676,7 @@ asmlinkage int vprintk_emit(int facility, int level, > level = default_message_loglevel; > > if (dict) > - lflags |= LOG_PREFIX|LOG_NEWLINE; > + lflags = LOG_PREFIX|LOG_NEWLINE; > > if (!(lflags & LOG_NEWLINE)) { > /* All the above changes make sense and I support them after all. > @@ -1686,9 +1690,8 @@ asmlinkage int vprintk_emit(int facility, int level, > if (cont_add(facility, level, text, text_len)) > printed_len += text_len; > else > - printed_len += log_store(facility, level, > - lflags | LOG_CONT, 0, > - dict, dictlen, text, text_len); > + printed_len += log_store(facility, level, lflags, 0, > + NULL, 0, text, text_len); > } else { > bool stored = false; > I do not see real benefit in this change. I think that it would cause more confusion than help. I would suggest to remove it. Then I will agree with this patch :-) Best Regards, Petr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 07/18/2014 05:53 AM, Petr Mládek wrote: >> @@ -1686,9 +1690,8 @@ asmlinkage int vprintk_emit(int facility, int level, >> > if (cont_add(facility, level, text, text_len)) >> > printed_len += text_len; >> > else >> > - printed_len += log_store(facility, level, >> > - lflags | LOG_CONT, 0, >> > - dict, dictlen, text, text_len); >> > + printed_len += log_store(facility, level, lflags, 0, >> > + NULL, 0, text, text_len); >> > } else { >> > bool stored = false; >> > > I do not see real benefit in this change. I think that it would cause > more confusion than help. I would suggest to remove it. Then I will > agree with this patch :-) Done. I'm going to add your Reviewed-by based on this. Please correct me if that's not what you want. -Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ff1c7ad..1ee1862 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1006,11 +1006,9 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev, prefix = false; if (msg->flags & LOG_CONT) { - if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE)) + if (prev & LOG_CONT) prefix = false; - - if (!(msg->flags & LOG_NEWLINE)) - newline = false; + newline = false; } do { @@ -1639,10 +1637,16 @@ asmlinkage int vprintk_emit(int facility, int level, text_len += vscnprintf(text + text_len, sizeof(textbuf) - text_len, fmt, args); - /* mark and strip a trailing newline */ + /* + * If there's a trailing newline, flag it and strip it off. + * Otherwise we assume this is a partial log message, to be + * continued with the next call. + */ if (text_len && text[text_len-1] == '\n') { text_len--; - lflags |= LOG_NEWLINE; + lflags = LOG_NEWLINE; + } else { + lflags = LOG_CONT; } /* strip kernel syslog prefix and extract log level or control flags */ @@ -1672,7 +1676,7 @@ asmlinkage int vprintk_emit(int facility, int level, level = default_message_loglevel; if (dict) - lflags |= LOG_PREFIX|LOG_NEWLINE; + lflags = LOG_PREFIX|LOG_NEWLINE; if (!(lflags & LOG_NEWLINE)) { /* @@ -1686,9 +1690,8 @@ asmlinkage int vprintk_emit(int facility, int level, if (cont_add(facility, level, text, text_len)) printed_len += text_len; else - printed_len += log_store(facility, level, - lflags | LOG_CONT, 0, - dict, dictlen, text, text_len); + printed_len += log_store(facility, level, lflags, 0, + NULL, 0, text, text_len); } else { bool stored = false;
Two log record flags--LOG_CONT and LOG_NEWLINE--are mutually exclusive. That is, one or the other is always set, but they are never both set at the same time in a log record flags field. What follows is a great deal of explanation that aims to prove this assertion. Having that knowledge allows us to simplify a bit of logic, and with a little more work (in follow-on patches) it allows us to do without some flag values, considerably simplifying things. Log record flags are held in the "cont" continuation buffer, as well as in "syslog_prev" and "console_prev". Those are discussed later. Other than that, log record flags are only set in log_store(): msg->flags = flags & 0x1f; There are 5 places log_store() is called: twice from cont_flush(); and three times from vprintk_emit(). Only two single-flag values are ever passed to cont_flush(): LOG_CONT; and LOG_NEWLINE. That passed-in value is provided to log_store() either as-is, or modified to include LOG_NOCONS. There are thus four possible flag combinations supplied to log_store() by cont_flush(): LOG_CONT; LOG_NEWLINE; LOG_CONT|LOG_NOCONS; or LOG_NEWLINE|LOG_NOCONS. The first call vprintk_emit() makes to log_store() passes a flags value of LOG_PREFIX|LOG_NEWLINE. The second and third calls pass a locally-computed "lflags" value, possibly with LOG_CONT added. The only possible flag combinations held in "lflags" are: 0; LOG_NEWLINE; LOG_PREFIX; or LOG_NEWLINE|LOG_PREFIX. If LOG_NEWLINE is not set, LOG_CONT flag is added in the call to log_store(). So there are four possible flag combinations supplied by cont_flush(): LOG_CONT; LOG_NEWLINE; LOG_PREFIX|LOG_CONT; or LOG_PREFIX|LOG_NEWLINE. Therefore log_store() is never provided (so never records) a flag value that contains both LOG_CONT and LOG_NEWLINE, and one of those flags is always present. Meanwhile, the "cont" flags field is only ever assigned value 0, or a value passed to cont_flush(). The value of cont.flags is only ever *used* if cont.flushed is true, and that only gets set after the cont.flags field is assigned to the value passed to cont_flush(). As mentioned above, cont_flush() is never provided more than one flag value, and it's always either LOG_NEWLINE or LOG_CONT. Therefore, for all intents and purposes, cont.flags only ever holds LOG_NEWLINE or LOG_CONT. The only values assigned to "syslog_prev" and "console_prev" are the initial value LOG_NEWLINE or the flags value from a log record. So none of these ever hold LOG_CONT and LOG_NEWLINE at the same time. This proves that at LOG_CONT and LOG_NEWLINE are in fact mutually exclusive flags. This patch makes the following changes: - Changes two spots in msg_print_txt() so they no longer bother checking for LOG_NEWLINE once its known that LOG_CONT is set. - Changes two |= assignments in vprintk_emit() to be simple assignments instead, because the result is known to be the same and it makes it obvious no other flags are involved. - Assigns LOG_CONT to "lflags" in vprintk_emit() if it does not contain LOG_NEWLINE (rather than just adding it at the time of the call to log_store()). - Adds a short explanatory comment. - Explicitly pass NULL rather than "dict" (and 0 as its length) to log_store() in one spot in vprintk_emit(), because we know the value of dict at that point is always NULL. Signed-off-by: Alex Elder <elder@linaro.org> --- kernel/printk/printk.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-)