s3: Do the ftruncate write cache optimization in one place

Instead of hand-tuning all the cases that are below this piece of code, this is
a general case that we can catch upfront.

diff --git a/source3/smbd/fileio.c b/source3/smbd/fileio.c
index c6094f902b0f53cc378f3b47ecfaef32447daa70..b4e8a1d5d4d0cb53a8124712d3ad4af87f06fde0 100644 (file)
--- a/source3/smbd/fileio.c
+++ b/source3/smbd/fileio.c
@@ -401,6 +401,37 @@ nonop=%u allocated=%u active=%u direct=%u perfect=%u readhits=%u\n",
 
        fsp->fh->pos = pos + n;
 
+       if ((n == 1) && (data[0] == '\0') && (pos > wcp->file_size)) {
+               int ret;
+
+               /*
+                * This is a 1-byte write of a 0 beyond the EOF and
+                * thus implicitly also beyond the current active
+                * write cache, the typical file-extending (and
+                * allocating, but we're using the write cache here)
+                * write done by Windows. We just have to ftruncate
+                * the file and rely on posix semantics to return
+                * zeros for non-written file data that is within the
+                * file length.
+                *
+                * We can not use wcp_file_size_change here because we
+                * might have an existing write cache, and
+                * wcp_file_size_change assumes a change to just the
+                * end of the current write cache.
+                */
+
+               wcp->file_size = pos + 1;
+               ret = SMB_VFS_FTRUNCATE(fsp, wcp->file_size);
+               if (ret == -1) {
+                       DEBUG(0,("wcp_file_size_change (%s): ftruncate of size %.0f"
+                                "error %s\n", fsp_str_dbg(fsp),
+                                (double)wcp->file_size, strerror(errno)));
+                       return -1;
+               }
+               return 1;
+       }
+
+
        /*
         * If we have active cache and it isn't contiguous then we flush.
         * NOTE: There is a small problem with running out of disk ....