afs: Reintroduce and use DFlushDCache()

This reverts commit 432ac5810e (afs:
Remove DFlushDCache()). This also re-adds the caller of DFlushDCache()
removed by commit 4045f3d535
(disconnected-shadow-directory-fixes-20090121), and the prototype
removed by commit 5ad1e6cb90 (dir:
Prototype and function name cleanup).

The removal of the DFlushDCache() call in commit 4045f3d535 seems like
a mistake. If the directory in question has dirty pages in memory, we
need to flush those to the cache before making a copy of the
directory's data, because we read the existing dir's data from the
cache. If we don't flush, afs_MakeShadowDir() might make a copy of the
dcache that is missing updates to the directory blob.

Change-Id: I4f26103b3db5e1ebdbe3324d2d9f67b39ab22e09
Reviewed-on: https://gerrit.openafs.org/15740
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>

src/afs/afs_buffer.c

@@ -515,6 +515,31 @@ DFlushBuffer(struct buffer *ab)
     afs_CFileClose(tfile);
 }
 
+void
+DFlushDCache(struct dcache *adc)
+{
+    int i;
+    struct buffer *tb;
+
+    ObtainReadLock(&afs_bufferLock);
+
+    for (i = 0; i <= PHPAGEMASK; i++)
+	for (tb = phTable[pHash(adc->index, i)]; tb != NULL; tb = tb->hashNext)
+	    if (tb->fid == adc->index) {
+		ObtainWriteLock(&tb->lock, 701);
+		tb->lockers++;
+		ReleaseReadLock(&afs_bufferLock);
+		if (tb->dirty) {
+		    DFlushBuffer(tb);
+		}
+		tb->lockers--;
+		ReleaseWriteLock(&tb->lock);
+		ObtainReadLock(&afs_bufferLock);
+	    }
+
+    ReleaseReadLock(&afs_bufferLock);
+}
+
 int
 DFlush(void)
 {

src/afs/afs_dcache.c

@@ -3879,6 +3879,9 @@ afs_MakeShadowDir(struct vcache *avc, struct dcache *adc)
 
     ReleaseWriteLock(&afs_xdcache);
 
+    /* Make sure and flush dir buffers back into the disk cache */
+    DFlushDCache(adc);
+
     /* Alloc a 4k block. */
     data = afs_osi_Alloc(4096);
     if (!data) {

src/afs/afs_prototypes.h

@@ -26,6 +26,7 @@ extern void afs_FreeAllAxs(struct axscache **headp);
 extern void shutdown_xscache(void);
 
 /* afs_buffer.c */
+extern void DFlushDCache(struct dcache *);
 extern void shutdown_bufferpackage(void);
 
 /* afs_call.c */