Linux, Programming, Bash & my thoughts...

systemtap script linux scsi timeout

Mahaveer Darade — Thu, 19 Jan 2012 09:44:58 +0000

1 #!/usr/bin/stap
2
3 probe begin{
4         print(“Starting probe, watching for SG_IO with threshold greater than “);
5             print($1 / 1000);
6                 print(” seconds.\nType control-c to stop.\n”);
7 }
8
9 probe kernel.function(“sg_io”)
10 {
11         if ($hdr->timeout > $1) {
12                    printf(“%s(%d) called sg_io with timeout = %d, greater than threshold\n”,
13                                         execname(), pid(), $hdr->timeout);
14         }
15         if ($q->sg_timeout > $1){
16                     printf(“%s(%d) called sg_io with sg_timeout = %d, greater than threshold\n”,
17                     execname(), pid(), $q->sg_timeout);
18         }
19 }
20
21 probe end {
22         print(“End probe\n”);
23 }

 281static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
 282                struct sg_io_hdr *hdr, fmode_t mode)
 283{
 284        unsigned long start_time;

memory map glibc pmap PROT_NONE

Mahaveer Darade — Wed, 18 Jan 2012 12:58:30 +0000

02:18 PM) mdarade: cld u tell me use cases of PROT_NONE except buffer overflow?
(06:02:43 PM) mdarade: & what decides size of areas protected with PROT_NONE?
(06:03:05 PM) mdarade: I mean i see upto 64K area being marked as PROT_NONE
(06:06:02 PM) siddhesh: PROT_NONE is basically just no permissions
(06:06:06 PM) siddhesh: use it as you will
(06:06:29 PM) siddhesh: typically they’re used to mark guard pages to catch buffr overflows
(06:07:02 PM) siddhesh: but it’s generally a good idea to mark pages as PTOR_NONE if they’re not intended to be used
(06:07:11 PM) siddhesh: libc uses it for its arena allocations
(06:08:34 PM) mdarade: size of areas protected with PROT_NONE is fixed?
(06:08:56 PM) siddhesh: whatever size you want, rounded to page size of course
(06:09:09 PM) mdarade: what is use in having 64k area protected with it?
(06:09:24 PM) siddhesh: depends on where it is used
(06:09:27 PM) siddhesh: where is it used?
(06:10:05 PM) mdarade: i see 132k anon allocation
(06:10:09 PM) mdarade: now to guard it
(06:10:24 PM) mdarade: why prot_none area size have to be 64?
(06:10:48 PM) siddhesh: where? which code?
(06:10:50 PM) mdarade: 64400k?
(06:11:08 PM) mdarade: pmap of java
(06:11:24 PM) siddhesh: ok, is it multithreaded?
(06:11:43 PM) mdarade: yeap
(06:12:13 PM) siddhesh: then those must be arenas allocated by libc for each thread
(06:12:21 PM) siddhesh: arenas act as heaps for each thread
(06:12:26 PM) siddhesh: to reduce locking between them
(06:12:54 PM) siddhesh: a new arena is always allocated with PROT_NONE and then parts of it given access as and when needed
(06:13:03 PM) siddhesh: for malloc requests
(06:13:07 PM) mdarade: got it thanks

Fraud happened in Magarpatta City, Hadapsar, Pune

Mahaveer Darade — Thu, 15 Dec 2011 16:29:18 +0000

This blog post is for those lucky ones who prefer to dig a little deeper before investing even a rupee. I want to share a story (which accidentally happened with me) while I was staying at A-35, Erica, Magarpatta city. When my employer provided accommodation was about to get over and I was looking out for some place I was contacted real estate agent/broker named Shahaji Somavanshi. He was a middleman whose job was to rent out someone else’s (actual owner) bungalow as he was working part time as a cab driver. Looking at him I realized I cannot trust this guy (thanks to my analytical skills) so I decided not to give deposit amount more than five thousand.

Finally I successfully negotiated the deal and stayed there for only two months. Even though serving one months notice he failed to return deposit back at the time of leaving. I contacted him after two weeks and again he promised some random date. This went happening until one day when I find out that he blocked my number. Finally I realized that it doesn’t make sense to contact this guy and its time to file a police complaint. Police managed to take money from that guy and I got my money back. Well not all of it but yes the process was all hectic, waste of energy and time.

Do remember name of those frauds.

Shahaji Somvanshi.

Santosh Kambale.

This post is my first contribution to society .

rsyslog patch

Mahaveer Darade — Thu, 15 Dec 2011 10:05:43 +0000

--- a/tools/syslogd.c	2011-12-14 14:38:53.557984324 +0530
+++ b/tools/syslogd.c	2011-12-14 14:38:45.011984782 +0530
@@ -3177,6 +3177,7 @@
 	uchar *LocalHostName;
 	uchar *LocalDomain;
 	uchar *LocalFQDNName;
+	int i;

 	/* first, parse the command line options. We do not carry out any actual work, just
 	 * see what we should do. This relieves us from certain anomalies and we can process
@@ -3316,9 +3317,22 @@
 		 */
 		hent = gethostbyname((char*)LocalHostName);
 		if(hent) {
+			if(hent->h_aliases) {
+				for (i=0; hent->h_aliases[i]; i++) {
+					if(strstr((hent->h_aliases[i]), (char*)LocalHostName)) {
+						//found hostname matching in aliases. use currently found one and break loop
+						 break;
+					}
+				}
+			}
+
 			free(LocalHostName);
-			CHKmalloc(LocalHostName = (uchar*)strdup(hent->h_name));
-
+			if(hent->h_aliases[i]) {
+				CHKmalloc(LocalHostName = (uchar*)strdup(hent->h_aliases[i]));
+			} else {
+				CHKmalloc(LocalHostName = (uchar*)strdup(hent->h_name));
+			}
+
 			if((p = (uchar*)strchr((char*)LocalHostName, '.')))
 			{
 				*p++ = '';

systemtap script

Mahaveer Darade — Thu, 15 Dec 2011 10:02:17 +0000

probe begin {
printf(“probe started”);
}

probe end {
printf(“probe finished”);
}

probe kernel.function(“radix_tree_insert”).return {
    if ($return) {
        printf(“%s: comm %s, pid %d, retval %d\n”, probefunc(), execname(), pid(), $return);
        print_backtrace();
    }
}

bit play with signed unsigned

Mahaveer Darade — Thu, 08 Dec 2011 09:47:05 +0000

[root@dhcp209-92 /]# cat size_t_size.c
#include
#include
int main() {
size_t len = -1;
/*   ssize_t chk = -1;
size_t toprint;
printf(“size of size_t is %d”, sizeof(size_t));
printf(“size of ssize_t is %d”, sizeof(ssize_t));
printf(“len is %d”, len);
toprint = (int) len;
printf(“toprint is %d”, toprint);
*/
if( len <= 0 || len == -1)
printf(” -1 if cond worked”);
//   if ( len == chk )
//       printf(” -1 cond worked”);
return 0;
}
[root@dhcp209-92 /]#

I don’t prefer to post output for different conditions as I want readers to try it out so that they understand it better .

C snippet showing conditional function prototype

Mahaveer Darade — Fri, 04 Nov 2011 11:40:21 +0000

1441         send_file_entry(f, fbuf, file,
1442 #ifdef SUPPORT_LINKS
1443                 symlink_name, symlink_len,
1444 #endif
1445                 flist->used, flist->ndx_start);

389 static void send_file_entry(int f, const char *fname, struct file_struct *file,
390 #ifdef SUPPORT_LINKS
391 const char *symlink_name, int symlink_len,
392 #endif
393 int ndx, int first_ndx)

signals linux ipc

Mahaveer Darade — Fri, 19 Aug 2011 09:26:31 +0000

0x00000fff922453cc in do_sigsuspend (set=0xfffc72dc668) at ../sysdeps/unix/sysv/linux/sigsuspend.c:63
63        return INLINE_SYSCALL (rt_sigsuspend, 2, CHECK_SIGSET (set), _NSIG / 8);

If pattern



is not present around above bt snippet then signal didn't occur and process which have
called sigsuspend has terminated abnormally.

How to use syslog for logging messages

Mahaveer Darade — Mon, 08 Aug 2011 12:18:22 +0000

[root@mdarade sample_code]# cat syslog_md.c #include #include #include int main() { char hello[]=”mahaveer darade”; openlog(“syslog_md”, LOG_PID, LOG_DAEMON ); syslog(LOG_INFO, “%s\n”, hello); printf(“pid is %d\n”, getpid()); closelog(); return 0; } [root@mdarade sample_code]#
[root@mdarade sample_code]# tail -f /var/log/messages Aug 8 17:43:14 mdarade syslog_md[4144]: mahaveer darade

Config files: /etc/syslog.conf, /etc/sysonfig/syslog

script to find files having ge number of lines

Mahaveer Darade — Thu, 04 Aug 2011 12:17:05 +0000

[mdarade@mdarade net-snmp-5.3.2.2]$ cat ~/scripts/find_files_having_specific_number_of_lines.sh
#!/usr/bin/env bash
find . -type f | while read line
do
        no_of_lines=`wc -l $line| cut -d" " -f1`;
        if [ $no_of_lines -ge $1 ] ; then
            ls -l "$line";
        fi
done
[mdarade@mdarade net-snmp-5.3.2.2]$