file change notification issues

Hal Roberts hroberts at
Thu Jan 23 15:56:00 GMT 2003

The purpose of this mail is to make sure no one else is 
working on / has already finished hacking samba's file 
change notification support to support notification of 
individual file changes.  If not, I plan on doing so forthwith.

More details:

I've been wrestling with samba for the past couple of weeks 
trying to get it to play nicely with IIS.  I've got IIS 
running with a samba share as the root directory, and 
everything works well except for asp caching.  When running 
from a samba share, IIS refuses to invalidate any cached 
asps, even if the cached asp is modified or even deleted or 

I've finally pegged the problem as samba file change 
notification support.  The cifs reference at:

indicates that samba should send back information about 
which files triggered a notification and why for any 
directory with notification running (for instance, 
/test/test.asp and FILE_ACTION_MODIFIED).  Samba should send 
back a list of such file/action records with one record for 
each file action that triggered the notification, up to the 
maximum as determined by the parameter count field in the 
request.  If the number of records would be greater that the 
max allowed, the samba server should return a 

The samba notification stuff as written does not keep track 
of which specific files were changed and just *always* 
returns the STATUS_NOTIFY_ENUM_DIR error.  This approach 
seems to work fine for handling windows explorer updates, 
but IIS and presumably other applications just drop these 
replies as errors.

I hacked the notify stuff to return a hard coded file / 
action record of a file I knew I was changing to test this 
theory, and the hack did indeed fix the problem -- when I 
changed the hard coded file, IIS immediately invalidated the 
asp cache for that file and loaded up the new file instead.

The big cost of adding individual file notifications will be 
the need to keep a bunch of file information in memory 
somewhere.  The current code just does a checksum of the 
file modification times of the monitored directory or relies 
on the dnotify kernel stuff, which only alerts on whole 
directories.  To figure which file changed, the system will 
have to keep the state of the monitored files in memory. 
There is a project called fam 
( that implements a daemon 
that handles this sort of thing for the general case, but it 
does not support all of the notifications that cifs requires 
(it does not support notifications of file access, for 
example), so the only way of implementing this correctly 
seems to be to write it from scratch.



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