From b87071d747fec80cdee7722a8bf57cf874725909 Mon Sep 17 00:00:00 2001
From: yoe <yoe>
Date: Mon, 31 Mar 2008 08:18:51 +0000
Subject: [PATCH] r331: Add code to detect whether a device is connected

---
 nbd-client.8.sgml |   20 ++++++++++++++++++++
 nbd-client.c      |   26 ++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/nbd-client.8.sgml b/nbd-client.8.sgml
index 25c23af..8d2f5d0 100644
--- a/nbd-client.8.sgml
+++ b/nbd-client.8.sgml
@@ -68,6 +68,10 @@ manpage.1: manpage.sgml
       <command>&dhpackage;</command>
       <arg choice=plain><option>-d <replaceable>nbd-device</replaceable></option></arg>
     </cmdsynopsis>
+    <cmdsynopsis>
+      <command>&dhpackage;</command>
+      <arg choice="plain"><option>-c <replaceable>nbd-device</replaceable></option></arg>
+    </cmdsynopsis>
   </refsynopsisdiv>
   <refsect1>
     <title>DESCRIPTION</title>
@@ -128,6 +132,22 @@ manpage.1: manpage.sgml
 	</listitem>
       </varlistentry>
       <varlistentry>
+	<term>-c</term>
+	<listitem>
+	  <para>Check whether the specified nbd device is
+	  connected.</para>
+	  <para>If the device is connected, &dhpackage; will exit
+	  with an exit state of 0 and print the PID of the &dhpackage;
+	  instance that connected it to stdout.
+	  <para>If the device is not
+	  connected or does not exist (for example because the nbd
+	  module was not loaded), &dhpackage; will exit with an exit
+	  state of 1 and not print anything on stdout.</para>
+	  <para>If an error occurred, &dhpackage; will exit with an exit
+	  state of 2, and not print anything on stdout either.</para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
 	<term>-d</term>
 	<listitem>
 	  <para>Disconnect the specified nbd device from the
diff --git a/nbd-client.c b/nbd-client.c
index 51927b1..4e4777b 100644
--- a/nbd-client.c
+++ b/nbd-client.c
@@ -28,6 +28,7 @@
 #include <syslog.h>
 #include <stdlib.h>
 #include <sys/mount.h>
+#include <errno.h>
 
 #ifndef __GNUC__
 #error I need GCC to work
@@ -37,6 +38,27 @@
 #define MY_NAME "nbd_client"
 #include "cliserv.h"
 
+int check_conn(char* devname) {
+	char buf[256];
+	int fd;
+	int len;
+	if(!strncmp(devname, "/dev/", 5)) {
+		devname+=5;
+	}
+	snprintf(buf, 256, "/sys/block/%s/pid", devname);
+	if((fd=open(buf, O_RDONLY))<0) {
+		if(errno==ENOENT) {
+			return 1;
+		} else {
+			return 2;
+		}
+	}
+	len=read(fd, buf, 256);
+	buf[len-1]='\0';
+	printf("%s\n", buf);
+	return 0;
+}
+
 int opennet(char *name, int port, int sdp) {
 	int sock;
 	struct sockaddr_in xaddrin;
@@ -191,6 +213,7 @@ int main(int argc, char *argv[]) {
 		fprintf(stderr, "nbd-client version %s\n", PACKAGE_VERSION);
 		fprintf(stderr, "Usage: nbd-client [bs=blocksize] [timeout=sec] host port nbd_device [-swap] [-persist]\n");
 		fprintf(stderr, "Or   : nbd-client -d nbd_device\n");
+		fprintf(stderr, "Or   : nbd-client -c nbd_device\n");
 		fprintf(stderr, "Default value for blocksize is 1024 (recommended for ethernet)\n");
 		fprintf(stderr, "Allowed values for blocksize are 512,1024,2048,4096\n"); /* will be checked in kernel :) */
 		fprintf(stderr, "Note, that kernel 2.4.2 and older ones do not work correctly with\n");
@@ -221,6 +244,9 @@ int main(int argc, char *argv[]) {
 		printf("done\n");
 		return 0;
 	}
+	if(strcmp(argv[0], "-c")==0) {
+		return check_conn(argv[1]);
+	}
 	
 	if (strncmp(argv[0], "bs=", 3)==0) {
 		blocksize=atoi(argv[0]+3);
-- 
1.7.10.4