Client-Side Caching Truncates Files During Creation (319509)

CAUSE

This problem may occur with any program that installs data into a cached network share.

The program calls CreateFile and sets the file size. The program then writes some data to the file, and this write results in a FastIO write.

The cache manager then issues paging IO writes to actually write the data to the server. At the end of these writes, client-side caching writes the data to the local copy of the file.

The program sends another CreateFile for the same file, and at the end of the processing of the second create, client-side caching finds that the file is stale (the timestamp is less than that of the file on the server). Because of this, the file is truncated. Client-side caching then sets the file status to SPARSE. This is done to make sure that the future reads and writes go to the server.

The program does a Close on this file. During the Close, the SPARSE flag is removed for SPARSE files that are not damaged (if the original file size matches the current file size). This means that the file is truncated, but it is no longer SPARSE.

The program sends another write at an offset into the file, and during the end of this write, client-side caching checks too see if the file is SPARSE or not. If the file is not SPARSE, the data is written to the local copy.

In this case, the file that has been created has all zeroes up to the last offset to which was written, and valid data after that. Now the file is not consistent with the file on the server, even though client-side caching interprets that it is.

he program reads some data, and because client-side caching interprets that the local copy is consistent with the server, it satisfies the read from the local copy, but the data that is returned is not correct. In a test program, the program quit.

   Date         Time   Version           Size     File name
   ---------------------------------------------------------
   21-Mar-2002  14:21  5.00.2195.5232    370,480  Mrxsmb.sys
   20-Mar-2002  05:14  5.00.2195.5200    131,920  Rdbss.sys