afs: Skip IsDCacheSizeOK for CDirty/VDIR

IsDCacheSizeOK currently can incorrectly flag a dcache as corrupted,
since the size of a dcache may not match the size of the underlying
file in a couple of RW conditions:

- If someone is writing to a file beyond EOF, the intermediate
  'sparse' area may be populated by 0-length dcaches until the data is
  written to the fileserver.

- Directories may be modified locally instead of being fetched from
  the fileserver, which can sometimes result in a directory blob of
  differing sizes.

To avoid false positives detecting dcache corruption, just skip the
IsDCacheSizeOK check for directories, and any file with pending writes
(CDirty).

Also add some extra information to the logging messages when this
"corruption" is detected, so false positives may be more easily
detected in the future.

Reviewed-on: https://gerrit.openafs.org/13747
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit e6b97b337bc97fdb1c8e4f1a0572c62dfc82d979)

Change-Id: I177020c37ba92d8730fe4c68ca610f1b39c3d69b
Reviewed-on: https://gerrit.openafs.org/15533
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>

src/afs/afs_dcache.c

@@ -1741,6 +1741,35 @@ IsDCacheSizeOK(struct dcache *adc, struct vcache *avc, afs_int32 chunk_bytes,
     afs_size_t expected_bytes;
     afs_size_t chunk_start = AFS_CHUNKTOBASE(adc->f.chunk);
 
+    if (vType(avc) == VDIR) {
+	/*
+	 * Directory blobs may be constructed locally (see afs_LocalHero), and
+	 * the size of the blob may differ slightly compared to what's on the
+	 * fileserver. So, skip size checks for directories.
+	 */
+	return 1;
+    }
+
+    if ((avc->f.states & CDirty)) {
+	/*
+	 * Our vcache may have writes that are local to our cache, but not yet
+	 * written to the fileserver. In such a situation, we may have dcaches
+	 * for that file that are "short". For example:
+	 *
+	 * Say we have a file that is 0 bytes long. A process opens that file,
+	 * and writes some data to offset 5M (keeping the file open). Another
+	 * process comes along and reads data from offset 1M. We'll try to
+	 * fetch data at offset 1M, and the fileserver will respond with 0
+	 * bytes, since our locally-written data hasn't been written to the
+	 * fileserver yet (on the fileserver, the file is still 0-bytes long).
+	 * So our dcache at offset 1M will have 0 bytes.
+	 *
+	 * So if CDirty is set, don't do any size/length checks at all, since
+	 * we have no idea if the avc length is valid.
+	 */
+	return 1;
+    }
+
     if (file_length < chunk_start) {
 	expected_bytes = 0;
 
@@ -1779,8 +1808,7 @@ IsDCacheSizeOK(struct dcache *adc, struct vcache *avc, afs_int32 chunk_bytes,
 	    }
 
 	    afs_warn("afs: Detected corrupt dcache for file %d.%u.%u.%u: chunk %d "
-		     "(offset %lu) has %d bytes, but it should have %lu bytes (file "
-		     "length %lu, DV %u, dcache mtime %u)\n",
+		     "(offset %lu) has %d bytes, but it should have %lu bytes\n",
 		     adc->f.fid.Cell,
 		     adc->f.fid.Fid.Volume,
 		     adc->f.fid.Fid.Vnode,
@@ -1788,12 +1816,21 @@ IsDCacheSizeOK(struct dcache *adc, struct vcache *avc, afs_int32 chunk_bytes,
 		     adc->f.chunk,
 		     (unsigned long)chunk_start,
 		     chunk_bytes,
-		     (unsigned long)expected_bytes,
+		     (unsigned long)expected_bytes);
+	    afs_warn("afs: (dcache %p, file length %lu, DV %u, dcache mtime %u, "
+		     "index %d, dflags 0x%x, mflags 0x%x, states 0x%x, vcache "
+		     "states 0x%x)\n",
+		     adc,
 		     (unsigned long)file_length,
 		     versionNo,
-		     mtime);
+		     mtime,
+		     adc->index,
+		     (unsigned)adc->dflags,
+		     (unsigned)adc->mflags,
+		     (unsigned)adc->f.states,
+		     avc->f.states);
 	    afs_warn("afs: Ignoring the dcache for now, but this may indicate "
-		     "corruption in the AFS cache\n");
+		     "corruption in the AFS cache, or a bug.\n");
 	}
 	return 0;
     }