rattrs: Replaced LFS3_tag_TAIL with single-recurse LFS3_tag_RATTRS

This originally started as an attempt to drop LFS3_tag_TAIL entirely,
but that didn't really go anywhere. Any attempt to work around the
double rattr-lists during mtree splits results in more mess than this
magic rattr.

But I did notice we only need to support "simple" rattrs during mtree
splits, which means we can just call lfs3_rbyd_appendrattrs to handle
these.

Maybe this will be problematic if we ever want to deduplicate
lfs3_mdir_commit___ and lfs3_rbyd_appendrattrs, but I don't see that
happening because of the different concerns (mdir-specific rattrs):

 function                code  stack  ctx
 lfs3_mdir_commit___     1052    744  396
 lfs3_rbyd_appendrattrs   142    584  388

The benefit of a single-recurse LFS3_tag_RATTRS:

- Simplifies lfs3_mdir_commit__, no more awkward loop recursion.

- May have other use cases for nesting simple rattrs?

Adds a bit of code:

                 code          stack          ctx
  before:       35316           2176          660
  after:        35320 (+0.0%)   2176 (+0.0%)  660 (+0.0%)

                 code          stack          ctx
  gbmap before: 38148           2192          772
  gbmap after:  38172 (+0.1%)   2192 (+0.0%)  772 (+0.0%)

lfs3.c

@@ -1945,9 +1945,6 @@ typedef uint8_t lfs3_count_t;
 // null rattr terminates rattr lists
 #define LFS3_RATTR_NULL ((lfs3_rattr_t)0)
 
-// alternatively, a tail rattr tail-recurses into another rattr list
-#define LFS3_RATTR_TAIL LFS3_RATTR(0, LFS3_tag_TAIL, 0)
-
 // create an attribute list
 #define LFS3_RATTRS(...) ((const lfs3_rattr_t[]){__VA_ARGS__})
 
@@ -8261,20 +8258,24 @@ static int lfs3_mdir_commit___(lfs3_t *lfs3, lfs3_mdir_t *mdir_,
             // is still included
             && (lfs3_size_t)(rid + 1) <= (lfs3_size_t)end_rid) {
 
-        const lfs3_rattr_t *r = rattrs;
+        for (const lfs3_rattr_t *r = rattrs;
-        recurse:;
+                *r;
-        for (; *r; r = lfs3_rattr_next(r, &rid)) {
+                r = lfs3_rattr_next(r, &rid)) {
             // we just happen to never split in an mdir commit
             LFS3_ASSERT(!(r > rattrs && lfs3_rattr_isinsert(r)));
 
-            // rattr lists can be chained, but only tail-recursively
+            // nested rattr list? we only support simple rattrs here
-            if (lfs3_rattr_tag(r) == LFS3_tag_TAIL) {
+            if (lfs3_rattr_tag(r) == LFS3_tag_RATTRS) {
                 const lfs3_rattr_t *rattrs_
                         = (const lfs3_rattr_t*)lfs3_rattr_arg(r, 0);
 
-                // switch to chained rattr-list
+                // recurse once
-                r = rattrs_;
+                int err = lfs3_rbyd_appendrattrs(lfs3, &mdir_->r,
-                goto recurse;
+                        rid, start_rid, end_rid,
+                        rattrs_);
+                if (err) {
+                    return err;
+                }
 
             // shrub tags append a set of attributes to an unrelated trunk
             // in our rbyd
@@ -9286,9 +9287,10 @@ static int lfs3_mdir_commit_(lfs3_t *lfs3, lfs3_mdir_t *mdir,
                     LFS3_RATTR_ARG(&mtree_),
                     // were we committing to the mroot? include any -1 rattrs
                     (mdir->mid <= -1)
-                        ? LFS3_RATTR_TAIL
+                        ? LFS3_RATTR(2, LFS3_tag_RATTRS, 0)
-                        : LFS3_RATTR_NULL,
+                        : LFS3_RATTR(2, LFS3_TAG_NULL, 0),
-                    LFS3_RATTR_ARG(rattrs)));
+                    LFS3_RATTR_ARG(rattrs),
+                    LFS3_RATTR_NULL));
         if (err) {
             LFS3_ASSERT(err != LFS3_ERR_RANGE);
             goto failed;

lfs3.h

@@ -829,7 +829,7 @@ enum lfs3_tag {
 
     // in-device only tags, these should never get written to disk
     LFS3_tag_INTERNAL       = 0x0000,
-    LFS3_tag_TAIL           = 0x0001,
+    LFS3_tag_RATTRS         = 0x0001,
     LFS3_tag_SHRUBCOMMIT    = 0x0002,
     LFS3_tag_GRMPUSH        = 0x0003,
     LFS3_tag_MOVE           = 0x0004,