vmcore-dmesg: Collect full dmesg regardless of logged_chars

logged_chars would be set to 0 by `dmesg -c`, but full dmesg is useful
for debugging. So instead of using logged_chars directly, we calculate
it by ourselves.

Now logged_chars is set to the minimum of log_end and log_buf_len, as
the same logic as crash utility is using.

Signed-off-by: Dangyi Liu <dliu@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 6 insertions, 0 deletions

diff --git a/vmcore-dmesg/vmcore-dmesg.c b/vmcore-dmesg/vmcore-dmesg.c
index f47ee11..0364636 100644
--- a/vmcore-dmesg/vmcore-dmesg.c
+++ b/vmcore-dmesg/vmcore-dmesg.c
@@ -540,6 +540,12 @@ static void dump_dmesg_legacy(int fd)
 		exit(53);
 	}
 
+	/*
+	 * To collect full dmesg including the part before `dmesg -c` is useful
+	 * for later debugging. Use same logic as what crash utility is using.
+	 */
+	logged_chars = log_end < log_buf_len ? log_end : log_buf_len;
+
 	write_to_stdout(buf + (log_buf_len -  logged_chars), logged_chars);
 }