Added lfs_rbyd_get, bumped hint back up to full during lookup

The idea behind the full hint is that we may stay on the current search
path, benefiting from a loaded cache. Though this should probably be
benchmarked eventually.

lfs.c

@@ -1172,7 +1172,7 @@ tryagain:;
         lfs_rtag_t alt;
         lfs_off_t jump;
         lfs_ssize_t delta = lfs_rbyd_readtag(lfs,
-                &lfs->pcache, &lfs->rcache, 2*4,
+                &lfs->pcache, &lfs->rcache, lfs->cfg->block_size,
                 rbyd->block, branch, &alt, &jump, NULL);
         if (delta < 0) {
             return delta;
@@ -1216,6 +1216,34 @@ tryagain:;
     }
 }
 
+static lfs_ssize_t lfs_rbyd_get(lfs_t *lfs, const lfs_rbyd_t *rbyd,
+        lfs_rtag_t tag, void *buffer, lfs_size_t size) {
+    lfs_off_t found_off;
+    lfs_size_t found_size;
+    lfs_srtag_t found_tag = lfs_rbyd_lookup(lfs, rbyd, tag,
+            &found_off, &found_size);
+    if (found_tag < 0) {
+        return found_tag;
+    }
+
+    // lookup finds the next-smallest tag, here we fail if it's not
+    // an exact match
+    if ((lfs_tag_t)found_tag != tag) {
+        return LFS_ERR_NOENT;
+    }
+
+    // note that it's highly likely the data is in our cache now
+    lfs_size_t delta = lfs_min(size, found_size);
+    int err = lfs_bd_read(lfs,
+            &lfs->pcache, &lfs->rcache, delta,
+            rbyd->block, found_off, buffer, delta);
+    if (err) {
+        return err;
+    }
+
+    return found_size;
+}
+
 static int lfs_rbyd_prog(lfs_t *lfs,
         lfs_cache_t *pcache, lfs_cache_t *rcache,
         lfs_block_t block, lfs_off_t off,
@@ -1438,7 +1466,7 @@ static int lfs_rbyd_commit(lfs_t *lfs, lfs_rbyd_t *rbyd,
             lfs_rtag_t alt;
             lfs_off_t jump;
             lfs_ssize_t delta = lfs_rbyd_readtag(lfs,
-                    &lfs->pcache, &lfs->rcache, 2*4,
+                    &lfs->pcache, &lfs->rcache, lfs->cfg->block_size,
                     block, branch, &alt, &jump, NULL);
             if (delta < 0) {
                 return delta;

tests/test_rbyd.toml

@@ -230,6 +230,151 @@ code = '''
             => LFS_ERR_NOENT;
 '''
 
+[cases.test_rbyd_get]
+in = 'lfs.c'
+code = '''
+    lfs_t lfs;
+    lfs_init(&lfs, cfg) => 0;
+
+    lfs_rbyd_t init_rbyd = {
+        .block = 0,
+        .trunk = 0,
+        .off = 0,
+        .rev = 1,
+        .crc = 0,
+        .count = 0,
+        .erased = true,
+    };
+    lfs_rbyd_t rbyd;
+    uint8_t buffer[4];
+
+    // try an empty commit
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd, NULL) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    // commit with one attribute
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd,
+            LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    assert(memcmp(buffer, &(uint32_t){0xaaaaaaaa}, 4) == 0);
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    assert(memcmp(buffer, &(uint32_t){0xaaaaaaaa}, 4) == 0);
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    // commit with two attributes
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd,
+            LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4,
+            LFS_MKRATTR(UATTR, 2, 0, &(uint32_t){0xbbbbbbbb}, 4, NULL))) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 3, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 3, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+'''
+
+[cases.test_rbyd_multi_get]
+in = 'lfs.c'
+code = '''
+    lfs_t lfs;
+    lfs_init(&lfs, cfg) => 0;
+
+    lfs_rbyd_t init_rbyd = {
+        .block = 0,
+        .trunk = 0,
+        .off = 0,
+        .rev = 1,
+        .crc = 0,
+        .count = 0,
+        .erased = true,
+    };
+    lfs_rbyd_t rbyd;
+    uint8_t buffer[4];
+
+    // try an empty commit
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd, NULL) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    // commit with one attribute
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd,
+            LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    assert(memcmp(buffer, &(uint32_t){0xaaaaaaaa}, 4) == 0);
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    assert(memcmp(buffer, &(uint32_t){0xaaaaaaaa}, 4) == 0);
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    // commit with two attributes
+    rbyd = init_rbyd;
+    lfs_bd_erase(&lfs, rbyd.block) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd,
+            LFS_MKRATTR(UATTR, 1, 0, &(uint32_t){0xaaaaaaaa}, 4, NULL)) => 0;
+    lfs_rbyd_commit(&lfs, &rbyd,
+            LFS_MKRATTR(UATTR, 2, 0, &(uint32_t){0xbbbbbbbb}, 4, NULL)) => 0;
+
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 3, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+
+    lfs_rbyd_fetch(&lfs, &rbyd, rbyd.block, NULL) => 0;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 1, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 2, 0), buffer, 4)
+            => 4;
+    lfs_rbyd_get(&lfs, &rbyd, LFS_MKRTAG(UATTR, 3, 0), buffer, 4)
+            => LFS_ERR_NOENT;
+'''
+
 [cases.test_rbyd_traverse]
 in = 'lfs.c'
 code = '''