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Message-ID: <CAKgNAkhQuugAOChSroXFgSPQ_=zyfFOZHzL3PGfU2SdmJcmj4w@mail.gmail.com>
Date: Thu, 29 Nov 2012 14:37:29 +0100
From: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To: Kay Sievers <kay@...y.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartmann <greg@...ah.com>,
Ingo Molnar <mingo@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length
record buffer
On Thu, Nov 29, 2012 at 2:28 PM, Kay Sievers <kay@...y.org> wrote:
> On Thu, Nov 29, 2012 at 2:18 PM, Michael Kerrisk (man-pages)
> <mtk.manpages@...il.com> wrote:
>> On Wed, Nov 28, 2012 at 6:51 PM, Kay Sievers <kay@...y.org> wrote:
>
>>> Before:
>>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 286965
>>> syslog(SYSLOG_ACTION_READ_CLEAR, "<12>"..., 1000000) = 24000
>>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 286965
>>>
>>> After:
>>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 90402
>>> syslog(SYSLOG_ACTION_READ_CLEAR, "<5>"..., 1000000) = 90402
>>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 0
>
>> I'm going to call my report yesterday bogus. Somewhere along the way,
>> I got confused while testing something, and my statement about 2.6.31
>> behavior is wrong: the 2.6.31 and 3.5 behaviors are the same. As such,
>> your patch is unneeded. Sorry for wasting your time.
>
> I think you have been right with your report. The above pasted
> before/after from the patch commit text is actually a result of real
> testing with current git. And your initial description sounds right,
> and the patch seems to produce the expected results here. I just
> confused the numbers in your report and wrongly parsed 2.6 > 3.6.
>
> Hmm, at least do far we did not blame anybody else than ourselves as
> confused. One of us at least is right, and it looks you have been, and
> I also think the patch is at least intended to be right. :)
Okay -- I'm pretty sure I am right about being wrong ;-).
Could you do some comparative testing please between 3.5 and pre-3.5.
I have a little test program below. When I rechecked 2.6.31 and 3.5
using this program I found the behavior was the same, which is why I
conclude my report is wrong. (And also, your proposed patch in
response to my bogus report produces different behavior from 2.6.31).
Thanks,
Michael
/*#* t_klogctl.c
klogctl(3) is the glibc interface for syslog(2)
*/
#include <sys/klog.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#define errMsg(msg) do { perror(msg); } while (0)
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)
#define fatal(msg) do { fprintf(stderr, "%s\n", msg); \
exit(EXIT_FAILURE); } while (0)
/* Close the log. Currently a NOP. */
#define SYSLOG_ACTION_CLOSE 0
/* Open the log. Currently a NOP. */
#define SYSLOG_ACTION_OPEN 1
/* Read from the log. */
#define SYSLOG_ACTION_READ 2
/* Read all messages remaining in the ring buffer. */
#define SYSLOG_ACTION_READ_ALL 3
/* Read and clear all messages remaining in the ring buffer */
#define SYSLOG_ACTION_READ_CLEAR 4
/* Clear ring buffer. */
#define SYSLOG_ACTION_CLEAR 5
/* Disable printk's to console */
#define SYSLOG_ACTION_CONSOLE_OFF 6
/* Enable printk's to console */
#define SYSLOG_ACTION_CONSOLE_ON 7
/* Set level of messages printed to console */
#define SYSLOG_ACTION_CONSOLE_LEVEL 8
/* Return number of unread characters in the log buffer */
#define SYSLOG_ACTION_SIZE_UNREAD 9
/* Return size of the log buffer */
#define SYSLOG_ACTION_SIZE_BUFFER 10
int
main(int argc, char *argv[])
{
int s;
#define BSIZE 500000
char buf[BSIZE];
if (argc < 2) {
fprintf(stderr, "Usage: %s command-num [arg]\n", argv[0]);
exit(EXIT_FAILURE);
}
int cmd;
cmd = atoi(argv[1]);
switch (cmd) {
case SYSLOG_ACTION_READ: /* 2 */
printf("SYSLOG_ACTION_READ\n");
s = klogctl(SYSLOG_ACTION_READ, buf,
(argc > 2) ? atoi(argv[2]) : BSIZE);
if (s == -1)
errExit("klogctl-READ");
printf("Return value: %d\n", s);
if (write(2, buf, s) != s)
errMsg("write");
break;
case SYSLOG_ACTION_READ_ALL: /* 3 */
case SYSLOG_ACTION_READ_CLEAR: /* 4 */
if (cmd == SYSLOG_ACTION_READ_CLEAR)
printf("SYSLOG_ACTION_READ_CLEAR\n");
else
printf("SYSLOG_ACTION_READ_ALL\n");
s = klogctl(cmd, buf,
(argc > 2) ? atoi(argv[2]) : BSIZE);
if (s == -1)
errExit("klogctl-READ_ALL/READ_CLEAR");
printf("Return value: %d\n", s);
if (write(2, buf, s) != s)
errMsg("write");
if (cmd == SYSLOG_ACTION_READ_CLEAR)
printf("Ring buffer cleared\n");
break;
case SYSLOG_ACTION_CLEAR: /* 5 */
printf("SYSLOG_ACTION_CLEAR\n");
s = klogctl(SYSLOG_ACTION_CLEAR, NULL, 0);
if (s == -1)
errExit("klogctl-CLEAR");
printf("Return value: %d\n", s);
printf("Ring buffer cleared\n");
break;
case SYSLOG_ACTION_SIZE_UNREAD: /* 9 */
printf("SYSLOG_ACTION_SIZE_UNREAD\n");
s = klogctl(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0);
if (s == -1)
errExit("klogctl-SIZE_UNREAD");
printf("Number of unread bytes: %d\n", s);
break;
case SYSLOG_ACTION_SIZE_BUFFER: /* 10 */
printf("SYSLOG_ACTION_SIZE_BUFFER\n");
s = klogctl(SYSLOG_ACTION_SIZE_BUFFER, NULL, 0);
if (s == -1)
errExit("klogctl-SIZE_BUFFER");
printf("Size of buffer: %d\n", s);
break;
default:
fatal("Bad command");
break;
}
exit(EXIT_SUCCESS);
}
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