In contrast to the now-obsolete smbfs, cifs does not send SMB_COM_FLUSH in response to an explicit fsync(2) to guarantee that all volatile data is written to stable storage on the server side, provided the server honors the request (which, to my knowledge, is true for Windows and Samba with 'strict sync' enabled). This patch modifies the cifs_fsync implementation to restore the fsync-behavior of smbfs by triggering SMB_COM_FLUSH after sending outstanding data on the client side to the server.
I inquired about this issue in the linux-cifs-client@lists.samba.org mailing list:
On Tue, Feb 10, 2009 at 12:35 AM, Jeff Layton jlayton@redhat.com wrote:
Horst Reiterer wrote:
Why was the explicit SMB_COM_FLUSH dropped in the new implementation?
It's not that it was "removed" per-se, just never implemented. Patches to add that capability would certainly be welcome.
I tested the patch with 2.6.28.6 and 2.6.18 (backported) on x86_64.
As of 2.6.30, the patch is part of mainline: