+ <div class="entry">
+ <div class="title"><a href="http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html">Testing if a file system can be used for home directories...</a></div>
+ <div class="date">2010-08-08 21:20</div>
+ <div class="body">
+<p>A few years ago, I was involved in a project planning to use
+Windows file servers as home directory servers for Debian
+Edu/Skolelinux machines. This was thought to be no problem, as the
+access would be through the SMB network file system protocol, and we
+knew other sites used SMB with unix and samba as the file server to
+mount home directories without any problems. But, after months of
+struggling, we had to conclude that our goal was impossible.</p>
+
+<p>The reason is simply that while SMB can be used for home
+directories when the file server is Samba running on Unix, this only
+work because of Samba have some extensions and the fact that the
+underlying file system is a unix file system. When using a Windows
+file server, the underlying file system do not have POSIX semantics,
+and several programs will fail if the users home directory where they
+want to store their configuration lack POSIX semantics.</p>
+
+<p>As part of this work, I wrote a small C program I want to share
+with you all, to replicate a few of the problematic applications (like
+OpenOffice.org and GCompris) and see if the file system was working as
+it should. If you find yourself in spooky file system land, it might
+help you find your way out again. This is the fs-test.c source:</p>
+
+<pre>
+/*
+ * Some tests to check the file system sematics. Used to verify that
+ * CIFS from a windows server do not work properly as a linux home
+ * directory.
+ * License: GPL v2 or later
+ *
+ * needs libsqlite3-dev and build-essential installed
+ * compile with: gcc -Wall -lsqlite3 -DTEST_SQLITE fs-test.c -o fs-test
+*/
+
+#define _FILE_OFFSET_BITS 64
+#define _LARGEFILE_SOURCE 1
+#define _LARGEFILE64_SOURCE 1
+
+#define _GNU_SOURCE /* for asprintf() */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef TEST_SQLITE
+/*
+ * Test sqlite open, as done by gcompris require the libsqlite3-dev
+ * package and linking with -lsqlite3. A more low level test is
+ * below.
+ * See also <URL: http://www.sqlite.org./faq.html#q5 >.
+ */
+#include <sqlite3.h>
+#define CREATE_TABLE_USERS \
+ "CREATE TABLE users (user_id INT UNIQUE, login TEXT, lastname TEXT, firstname TEXT, birthdate TEXT, class_id INT ); "
+int test_sqlite_open(void) {
+ char *zErrMsg;
+ char *name = "testsqlite.db";
+ sqlite3 *db=NULL;
+ unlink(name);
+ int rc = sqlite3_open(name, &db);
+ if( rc ){
+ printf("error: sqlite open of %s failed: %s\n", name, sqlite3_errmsg(db));
+ sqlite3_close(db);
+ return -1;
+ }
+
+ /* create tables */
+ rc = sqlite3_exec(db,CREATE_TABLE_USERS, NULL, 0, &zErrMsg);
+ if( rc != SQLITE_OK ){
+ printf("error: sqlite table create failed: %s\n", zErrMsg);
+ sqlite3_close(db);
+ return -1;
+ }
+ printf("info: sqlite worked\n");
+ sqlite3_close(db);
+ return 0;
+}
+#endif /* TEST_SQLITE */
+
+/*
+ * Demonstrate locking issue found in gcompris using sqlite3. This
+ * work with ext3, but not with cifs server on Windows 2003. This is
+ * done in the sqlite3 library.
+ * See also
+ * <URL:http://www.cygwin.com/ml/cygwin/2001-08/msg00854.html> and the
+ * POSIX specification
+ * <URL:http://www.opengroup.org/onlinepubs/009695399/functions/fcntl.html>.
+ */
+int test_gcompris_locking(void) {
+ struct flock fl;
+ char *name = "testsqlite.db";
+ unlink(name);
+ int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, 0644);
+ printf("info: testing fcntl locking\n");
+
+ fl.l_whence = SEEK_SET;
+ fl.l_pid = getpid();
+ printf(" Read-locking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_RDLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Read-locking 510 byte from 1073741826");
+ fl.l_start = 1073741826;
+ fl.l_len = 510;
+ fl.l_type = F_RDLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Unlocking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_UNLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Write-locking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_WRLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Write-locking 510 byte from 1073741826");
+ fl.l_start = 1073741826;
+ fl.l_len = 510;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Unlocking 2 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 2;
+ fl.l_type = F_UNLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ close(fd);
+ return 0;
+}
+
+/*
+ * Test if permissions of freshly created directories allow entries
+ * below them. This was a problem with OpenOffice.org and gcompris.
+ * Mounting with option 'sync' seem to solve this problem while
+ * slowing down file operations.
+ */
+int test_subdirectory_creation(void) {
+#define LEVELS 5
+ char *path = strdup("test");
+ char *dirs[LEVELS];
+ int level;
+ printf("info: testing subdirectory creation\n");
+ for (level = 0; level < LEVELS; level++) {
+ char *newpath = NULL;
+ if (-1 == mkdir(path, 0777)) {
+ printf(" error: Unable to create directory '%s': %s\n",
+ path, strerror(errno));
+ break;
+ }
+ asprintf(&newpath, "%s/%s", path, "test");
+ free(path);
+ path = newpath;
+ }
+ return 0;
+}
+
+/*
+ * Test if symlinks can be created. This was a problem detected with
+ * KDE.
+ */
+int test_symlinks(void) {
+ printf("info: testing symlink creation\n");
+ unlink("symlink");
+ if (-1 == symlink("file", "symlink"))
+ printf(" error: Unable to create symlink\n");
+ return 0;
+}
+
+int main(int argc, char **argv) {
+ printf("Testing POSIX/Unix sematics on file system\n");
+ test_symlinks();
+ test_subdirectory_creation();
+#ifdef TEST_SQLITE
+ test_sqlite_open();
+#endif /* TEST_SQLITE */
+ test_gcompris_locking();
+ return 0;
+}
+</pre>
+
+<p>When everything is working, it should print something like
+this:</p>
+
+<pre>
+Testing POSIX/Unix sematics on file system
+info: testing symlink creation
+info: testing subdirectory creation
+info: sqlite worked
+info: testing fcntl locking
+ Read-locking 1 byte from 1073741824
+ Read-locking 510 byte from 1073741826
+ Unlocking 1 byte from 1073741824
+ Write-locking 1 byte from 1073741824
+ Write-locking 510 byte from 1073741826
+ Unlocking 2 byte from 1073741824
+</pre>
+
+<p>I do not remember the exact details of the problems we saw, but one
+of them was with locking, where if I remember correctly, POSIX allow a
+read-only lock to be upgraded to a read-write lock without unlocking
+the read-only lock (while Windows do not). Another was a bug in the
+CIFS/SMB client implementation in the Linux kernel where directory
+meta information would be wrong for a fraction of a second, making
+OpenOffice.org fail to create its deep directory tree because it was
+not allowed to create files in its freshly created directory.</p>
+
+<p>Anyway, here is a nice tool for your tool box, might you never need
+it. :)</p>
+</div>
+ <div class="tags">
+
+
+
+ Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.
+
+ </div>
+ </div>
+ <div class="padding"></div>
+
<div class="entry">
<div class="title"><a href="http://people.skolelinux.org/pere/blog/Autodetecting_Client_setup_for_roaming_workstations_in_Debian_Edu.html">Autodetecting Client setup for roaming workstations in Debian Edu</a></div>
<div class="date">2010-08-07 14:45</div>
- Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian">debian</a>, <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/ldap">ldap</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.
-
- </div>
- </div>
- <div class="padding"></div>
-
- <div class="entry">
- <div class="title"><a href="http://people.skolelinux.org/pere/blog/Idea_for_storing_LTSP_configuration_in_LDAP.html">Idea for storing LTSP configuration in LDAP</a></div>
- <div class="date">2010-07-11 22:00</div>
- <div class="body">
-<p>Vagrant mentioned on IRC today that ltsp_config now support
-sourcing files from /usr/share/ltsp/ltsp_config.d/ on the thin
-clients, and that this can be used to fetch configuration from LDAP if
-Debian Edu choose to store configuration there.</p>
-
-<p>Armed with this information, I got inspired and wrote a test module
-to get configuration from LDAP. The idea is to look up the MAC
-address of the client in LDAP, and look for attributes on the form
-ltspconfigsetting=value, and use this to export SETTING=value to the
-LTSP clients.</p>
-
-<p>The goal is to be able to store the LTSP configuration attributes
-in a "computer" LDAP object used by both DNS and DHCP, and thus
-allowing us to store all information about a computer in one place.</p>
-
-<p>This is a untested draft implementation, and I welcome feedback on
-this approach. A real LDAP schema for the ltspClientAux objectclass
-need to be written. Comments, suggestions, etc?</p>
-
-<blockquote><pre>
-# Store in /opt/ltsp/$arch/usr/share/ltsp/ltsp_config.d/ldap-config
-#
-# Fetch LTSP client settings from LDAP based on MAC address
-#
-# Uses ethernet address as stored in the dhcpHost objectclass using
-# the dhcpHWAddress attribute or ethernet address stored in the
-# ieee802Device objectclass with the macAddress attribute.
-#
-# This module is written to be schema agnostic, and only depend on the
-# existence of attribute names.
-#
-# The LTSP configuration variables are saved directly using a
-# ltspConfig prefix and uppercasing the rest of the attribute name.
-# To set the SERVER variable, set the ltspConfigServer attribute.
-#
-# Some LDAP schema should be created with all the relevant
-# configuration settings. Something like this should work:
-#
-# objectclass ( 1.1.2.2 NAME 'ltspClientAux'
-# SUP top
-# AUXILIARY
-# MAY ( ltspConfigServer $ ltsConfigSound $ ... )
-
-LDAPSERVER=$(debian-edu-ldapserver)
-if [ "$LDAPSERVER" ] ; then
- LDAPBASE=$(debian-edu-ldapserver -b)
- for MAC in $(LANG=C ifconfig |grep -i hwaddr| awk '{print $5}'|sort -u) ; do
- filter="(|(dhcpHWAddress=ethernet $MAC)(macAddress=$MAC))"
- ldapsearch -h "$LDAPSERVER" -b "$LDAPBASE" -v -x "$filter" | \
- grep '^ltspConfig' | while read attr value ; do
- # Remove prefix and convert to upper case
- attr=$(echo $attr | sed 's/^ltspConfig//i' | tr a-z A-Z)
- # bass value on to clients
- eval "$attr=$value; export $attr"
- done
- done
-fi
-</pre></blockquote>
-
-<p>I'm not sure this shell construction will work, because I suspect
-the while block might end up in a subshell causing the variables set
-there to not show up in ltsp-config, but if that is the case I am sure
-the code can be restructured to make sure the variables are passed on.
-I expect that can be solved with some testing. :)</p>
-
-<p>If you want to help out with implementing this for Debian Edu,
-please contact us on debian-edu@lists.debian.org.</p>
-
-<p>Update 2010-07-17: I am aware of another effort to store LTSP
-configuration in LDAP that was created around year 2000 by
-<a href="http://www.pcxperience.com/thinclient/documentation/ldap.html">PC
-Xperience, Inc., 2000</a>. I found its
-<a href="http://people.redhat.com/alikins/ltsp/ldap/">files</a> on a
-personal home page over at redhat.com.</p>
-</div>
- <div class="tags">
-
-
-
Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian">debian</a>, <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/ldap">ldap</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.
</div>
<li><a href="http://people.skolelinux.org/pere/blog/archive/2010/07/">July (12)</a></li>
-<li><a href="http://people.skolelinux.org/pere/blog/archive/2010/08/">August (2)</a></li>
+<li><a href="http://people.skolelinux.org/pere/blog/archive/2010/08/">August (3)</a></li>
</ul></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/debian">debian (35)</a></li>
- <li><a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (38)</a></li>
+ <li><a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (39)</a></li>
- <li><a href="http://people.skolelinux.org/pere/blog/tags/english">english (53)</a></li>
+ <li><a href="http://people.skolelinux.org/pere/blog/tags/english">english (54)</a></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/fiksgatami">fiksgatami (1)</a></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/norsk">norsk (71)</a></li>
- <li><a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug (90)</a></li>
+ <li><a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug (91)</a></li>
<li><a href="http://people.skolelinux.org/pere/blog/tags/opphavsrett">opphavsrett (14)</a></li>
</div>
<p style="text-align: right">
-Created by <a href="http://steve.org.uk/Software/chronicle">Chronicle v3.2</a>
+Created by <a href="http://steve.org.uk/Software/chronicle">Chronicle v3.7</a>
</p>
</body>
</html>
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