metadisp: new translator for data and metadata separation

Summary:

feature/metadisp is an xlator for performing "metadata dispersal" across
multiple children. it does this by flattening the complex
POSIX paths into /$GFID style paths, then forwarding the
metadata operations to its first child and forwarding the
data operations to its second child.

The purpose of this xlator is to allow separation of data and metadata,
in cases where metadata might be stored in another format (embedded kv?),
on another disk (ssd), on another host (dht2).

Change-Id: I392c8bd0c867a3237d144aea327323f700a2728d
Updates: #816
Signed-Off-By: Sheena Artrip <sheenobu@fb.com>
Tested-By: Amar Tumballi <amar@kadalu.io>

1 files changed, 65 insertions, 0 deletions

diff --git a/xlators/features/metadisp/src/metadisp-readdir.c b/xlators/features/metadisp/src/metadisp-readdir.c
new file mode 100644
index 00000000000..5f840b1e88f
--- /dev/null
+++ b/xlators/features/metadisp/src/metadisp-readdir.c
@@ -0,0 +1,65 @@
+#include "metadisp.h"
+
+/**
+ * With a change to the posix xlator, readdir and readdirp are shockingly
+ * simple.
+ *
+ * The issue with separating the backend data of the files
+ * with the metadata is that readdirs must now read from multiple sources
+ * to coalesce the directory entries.
+ *
+ * The way we do this is to tell the METADATA_CHILD that when it's
+ * running readdirp, each file entry should have a stat wound to
+ * 'stat-source-of-truth'.
+ *
+ * see metadisp_stat for how it handles winds _from_posix.
+ */
+
+int32_t
+metadisp_readdir(call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+                 off_t off, dict_t *xdata)
+{
+    METADISP_TRACE(".");
+    /*
+     * Always use readdirp, even if the original was readdir. Why? Because NFS.
+     * There are multiple translations between Gluster, UNIX, and NFS stat
+     * structures in that path. One of them uses the type etc. from the stat
+     * structure, which is only filled in by readdirp. If we use readdir, the
+     * entries do actually go all the way back to the client and are visible in
+     * getdents, but then the readdir throws them away because of the
+     * uninitialized type.
+     */
+    GF_UNUSED int32_t ret;
+    if (!xdata) {
+        xdata = dict_new();
+    }
+
+    // ret = dict_set_int32 (xdata, "list-xattr", 1);
+
+    // I'm my own source of truth!
+    ret = dict_set_static_ptr(xdata, "stat-source-of-truth", (void *)this);
+
+    STACK_WIND(frame, default_readdirp_cbk, METADATA_CHILD(this),
+               METADATA_CHILD(this)->fops->readdirp, fd, size, off, xdata);
+
+    return 0;
+}
+
+int32_t
+metadisp_readdirp(call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+                  off_t off, dict_t *xdata)
+{
+    METADISP_TRACE(".");
+    if (!xdata) {
+        xdata = dict_new();
+    }
+    GF_UNUSED int32_t ret;
+    // ret = dict_set_int32 (xdata, "list-xattr", 1);
+
+    // I'm my own source of truth!
+    ret = dict_set_static_ptr(xdata, "stat-source-of-truth", (void *)this);
+
+    STACK_WIND(frame, default_readdirp_cbk, METADATA_CHILD(this),
+               METADATA_CHILD(this)->fops->readdirp, fd, size, off, xdata);
+    return 0;
+}