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SubjectRe: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer
Hi Kay,

On Thu, May 3, 2012 at 2:29 AM, Kay Sievers <kay@vrfy.org> wrote:
> From: Kay Sievers <kay@vrfy.org>
[...]
> case SYSLOG_ACTION_SIZE_UNREAD:
> - error = log_end - log_start;
> + raw_spin_lock_irq(&logbuf_lock);
> + if (syslog_seq < log_first_seq) {
> + /* messages are gone, move to first one */
> + syslog_seq = log_first_seq;
> + syslog_idx = log_first_idx;
> + }
> + if (from_file) {
> + /*
> + * Short-cut for poll(/"proc/kmsg") which simply checks
> + * for pending data, not the size; return the count of
> + * records, not the length.
> + */
> + error = log_next_idx - syslog_idx;
> + } else {
> + u64 seq;
> + u32 idx;
> +
> + error = 0;
> + seq = syslog_seq;
> + idx = syslog_idx;
> + while (seq < log_next_seq) {
> + error += syslog_print_line(idx, NULL, 0);
> + idx = log_next(idx);
> + seq++;
> + }
> + }
> + raw_spin_unlock_irq(&logbuf_lock);
> break;
[...]

It looks as though the changes here have broken SYSLOG_ACTION_SIZE_UNREAD.

On a 2.6.31 system, immediately after SYSLOG_ACTION_READ_CLEAR, a
SYSLOG_ACTION_SIZE_UNREAD returns 0.

On 3.5, immediately after SYSLOG_ACTION_READ_CLEAR, the value returned
by SYSLOG_ACTION_SIZE_UNREAD is unchanged (i.e., assuming that the
value returned was non-zero before SYSLOG_ACTION_SIZE_UNREAD, it is
still nonzero afterward), even though a subsequent
SYSLOG_ACTION_READ_CLEAR indicates that there are zero bytes to read.

(All tests conducted with (r)syslogd stopped.)

Cheers,

Michael


--
Michael Kerrisk Linux man-pages maintainer;
http://www.kernel.org/doc/man-pages/


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