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printk: tweak do_syslog() to match comments

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In do_syslog() there's a path used by kmsg_poll() and kmsg_read() that
only needs to know whether there's any data available to read (and not
its size).  These callers only check for non-zero return.  As a
shortcut, do_syslog() returns the difference between what has been
logged and what has been "seen."

The comments say that the "count of records" should be returned but it's
not.  Instead it returns (log_next_idx - syslog_idx), which is a
difference between buffer offsets--and the result could be negative.

The behavior is the same (it'll be zero or not in the same cases), but
the count of records is more meaningful and it matches what the comments
say.  So change the code to return that.

Signed-off-by: Alex Elder <elder@linaro.org>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Joe Perches <joe@perches.com>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alex Elder 2014-08-06 16:08:59 -07:00 committed by Linus Torvalds
parent 23b2899f7f
commit e97e1267e9
1 changed files with 1 additions and 1 deletions
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2
kernel/printk/printk.c
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@ -1351,7 +1351,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
* for pending data, not the size; return the count of
* records, not the length.
*/
error = log_next_idx - syslog_idx;
error = log_next_seq - syslog_seq;
} else {
u64 seq = syslog_seq;
u32 idx = syslog_idx;