From: Petter Reinholdtsen <pere@hungry.com>
Date: Thu, 26 Aug 2010 11:29:38 +0000 (+0000)
Subject: New entry.
X-Git-Url: https://pere.pagekite.me/gitweb/homepage.git/commitdiff_plain/87d51c4f2a066ecd1118f0678f03fb1dcb0cf31a?ds=sidebyside

New entry.
---

diff --git a/blog/data/2010-08-26-fs-sematics.txt b/blog/data/2010-08-26-fs-sematics.txt
new file mode 100644
index 0000000000..d522c01509
--- /dev/null
+++ b/blog/data/2010-08-26-fs-sematics.txt
@@ -0,0 +1,96 @@
+Title: Broken umask handling with sshfs
+Tags: english, nuug, debian edu
+Date: 2010-08-26 13:30
+
+<p>My file system sematics program
+<a href="http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html">presented
+a few days ago</a> is very useful to verify that a file system can
+work as a unix home directory,and today I had to extend it a bit.  I'm
+looking into alternatives for home directory access here at the
+University of Oslo, and one of the options is sshfs.  My friend
+Finn-Arne mentioned a while back that they had used sshfs with Debian
+Edu, but stopped because of problems.  I asked today what the problems
+where, and he mentioned that sshfs failed to handle umask properly.
+Trying to detect the problem I wrote this addition to my fs testing
+script:</p>
+
+<pre>
+mode_t touch_get_mode(const char *name, mode_t mode) {
+  mode_t retval = 0;
+  int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, mode);
+  if (-1 != fd) {
+    unlink(name);
+    struct stat statbuf;
+    if (-1 != fstat(fd, &statbuf)) {
+      retval = statbuf.st_mode & 0x1ff;
+    }
+    close(fd);
+  }
+  return retval;
+}
+
+/* Try to detect problem discovered using sshfs */
+int test_umask(void) {
+  printf("info: testing umask effect on file creation\n");
+
+  mode_t orig_umask = umask(000);
+  mode_t newmode;
+  if (0666 != (newmode = touch_get_mode("foobar", 0666))) {
+    printf("  error: Wrong file mode %o when creating using mode 666 and umask 000\n",
+           newmode);
+  }
+  umask(007);
+  if (0660 != (newmode = touch_get_mode("foobar", 0666))) {
+    printf("  error: Wrong file mode %o when creating using mode 666 and umask 007\n",
+           newmode);
+  }
+
+  umask (orig_umask);
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  [...]
+  test_umask();
+  return 0;
+}
+</pre>
+
+<p>Sure enough.  On NFS to a netapp, I get this result:</p>
+
+<pre>
+Testing POSIX/Unix sematics on file system
+info: testing symlink creation
+info: testing subdirectory creation
+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
+info: testing umask effect on file creation
+</pre>
+
+<p>When mounting the same directory using sshfs, I get this
+result:</p>
+
+<pre>
+Testing POSIX/Unix sematics on file system
+info: testing symlink creation
+info: testing subdirectory creation
+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
+info: testing umask effect on file creation
+  error: Wrong file mode 644 when creating using mode 666 and umask 000
+  error: Wrong file mode 640 when creating using mode 666 and umask 007
+</pre>
+
+<p>So, I can conclude that sshfs is better than smb to a Netapp or a
+Windows server, but not good enough to be used as a home
+directory.</p>