Timed permission problems on CIFS

At work we use CIFS to mount some folders of our NAS into Linux servers. Since some days we had real problems using the Typo3 extension manager: Whenever we tried to install an extension, we got "Operation not permitted" and "No permission" errors when the install tool tried to create folders and chmod them.

I wrote a small php script which reproduced the problem:

While creating the folder worked, neither changing permissions nor creating the subfolder did. The same script ran fine on an NFS mount, though - so it wasn't a server problem. File and directory permissions all were ok.

After some experimenation I found out that inserting a sleep(1); call fixed the problem, and that I could go down to 900ms using usleep();. A colleague explained to me that this was most likely be a caching issue: CIFS caches inode data, and by not clearing the cache after creating a directory, it still sees the folder as non-existing - resulting in a "operation not permitted" error. The 1 second sleep fixed that.

$searchengine delivered some results about using forcedirectio or directio mount options, the mount.cifs man page told me to use direct. Nothing helped.

The solution came to me when scrolling though /usr/src/linux/fs/cifs/README:

  If set to one, inode information is kept cached
  for one second improving performance of lookups
  (default 1)

A echo "0" > /proc/fs/cifs/LookupCacheEnable did the trick.

Update a day later

forcedirectio or one of the other two aliases did actually do something! When I came into office this morning, I had 500 mails of cronjob errors, all with the same message:

Failed loading /usr/local/lib/php/extensions/no-debug-non-zts-20060613/xdebug.so: /usr/local/lib/php/extensions/no-debug-non-zts-20060613/xdebug.so: failed to map segment from shared object: No such device

Further, strace revealed:

3, 0) = -1 ENODEV (No such device)

Mark Karpeles of #php.pecl gave me the hint I needed: man mmap tells us:

The underlying filesystem of the specified file does not support memory mapping.

And that was it. After disabling the three *direct* options in fstab, it worked.

Written by Christian Weiske.

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