Hi, I found there is a 'log' command problem related to handling the ring buffer, and this patch fixes it. The ring buffer can be cleared by klogctl(2) from a user process, but current crash utility does not consider this case. The following output of current crash utility is example of this case. You see there is the panic message "SysRq : Trigger a crashdump" inside even if it should be output in the end: crash > log [snip] exception[8291] trap divide error rip:4004c0 rsp:7fffb56cdf60 error:0 exception[8293] trap divide error rip:4004c0 rsp:7fffbb0628f0 error:0 SysRq : Trigger a crashdump 14 15) *0, disabled. ACPI: PCI Interrupt Link [LNKF] (IRQs 4 5 6 7 10 14 15) *0, disabled. ACPI: PCI Interrupt Link [LNKG] (IRQs 3 4 5 6 7 10 14 15) *0, disabled. [snip] crash > This patch fixes this invalid output to the folloing: crash > log [snip] exception[8291] trap divide error rip:4004c0 rsp:7fffb56cdf60 error:0 exception[8293] trap divide error rip:4004c0 rsp:7fffbb0628f0 error:0 SysRq : Trigger a crashdump crash> I have one concern about this fixing: If applying this patch, 'log' command outputs the log data from the time of klogctl(2) call for the log clearance. If making the other patch, we will be able to extract the former log data, because a kernel does not clear the ring buffer and it just clears "logged_chars" internally. I feel this patch is better, because the log data can be cleared only by a root user and he decided the former log data is unnecessary. What do you think of this? Thanks Ken'ichi Ohmichi Signed-off-by: Ken'ichi Ohmichi <oomichi(a)mxs.nes.nec.co.jp&gt; --- --- crash-4.0-7.7/kernel.c.orig 2009-02-06 01:13:43.000000000 +0900 +++ crash-4.0-7.7/kernel.c 2009-02-17 12:07:33.000000000 +0900 @@ -3364,13 +3364,13 @@ cmd_log(void) void dump_log(int msg_level) { - int i; + int i, j; ulong log_buf, logged_chars; char *buf; char last; ulong index; struct syment *nsp; - int log_wrap, loglevel, log_buf_len; + int loglevel, log_buf_len; if (symbol_exists("log_buf_len")) { get_symbol_data("log_buf_len", sizeof(int), &log_buf_len); @@ -3391,29 +3391,28 @@ dump_log(int msg_level) } buf = GETBUF(log_buf_len); - log_wrap = FALSE; get_symbol_data("logged_chars", sizeof(ulong), &logged_chars); readmem(log_buf, KVADDR, buf, log_buf_len, "log_buf contents", FAULT_ON_ERROR); + get_symbol_data("log_end", sizeof(ulong), &index); + index &= (log_buf_len - 1); if (logged_chars < log_buf_len) { - index = 0; - } else { - get_symbol_data("log_end", sizeof(ulong), &index); - index &= log_buf_len-1; - } + if (logged_chars <= index) + index -= logged_chars; + else + index = log_buf_len - (logged_chars - index); + } if ((logged_chars < log_buf_len) && (index == 0) && (buf[index] == '<')) loglevel = TRUE; else loglevel = FALSE; - if (index != 0) - log_wrap = TRUE; + for (i = index, j = 0; j < logged_chars; i++, j++) { + if (i >= log_buf_len) + i = 0; -wrap_around: - - for (i = index; i < log_buf_len; i++) { if (loglevel && !msg_level) { switch (buf[i]) { @@ -3444,13 +3443,6 @@ wrap_around: } } - if (log_wrap) { - log_buf_len = index; - index = 0; - log_wrap = FALSE; - goto wrap_around; - } - if (last != '\n') fprintf(fp, "\n");