Stop wear-leveling during migration

Stop proactively relocate blocks during migrations, this can cause a number of
failure states such: clobbering the v1 superblock if we relocate root, and
invalidating directory pointers if we relocate the head of a directory. On top
of this, relocations increase the overall complexity of lfs_migration, which is
already a delicate operation.

lfs.c

@@ -1503,9 +1503,13 @@ static int lfs_dir_compact(lfs_t *lfs,
                 }
             }
 #ifdef LFS_MIGRATE
-        } else if (lfs_pair_cmp(dir->pair, lfs->root) == 0 && lfs->lfs1) {
-            // we can't relocate our root during migrations, as this would
-            // cause the superblock to get updated, which would clobber v1
+        } else if (lfs->lfs1) {
+            // do not proactively relocate blocks during migrations, this
+            // can cause a number of failure states such: clobbering the
+            // v1 superblock if we relocate root, and invalidating directory
+            // pointers if we relocate the head of a directory. On top of
+            // this, relocations increase the overall complexity of
+            // lfs_migration, which is already a delicate operation.
 #endif
         } else {
             // we're writing too much, time to relocate
@@ -2064,10 +2068,14 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
     dir->pos = lfs_min(2, off);
     off -= dir->pos;
 
-    while (off != 0) {
-        dir->id = lfs_min(dir->m.count, off);
-        dir->pos += dir->id;
-        off -= dir->id;
+    // skip superblock entry
+    dir->id = (off > 0 && lfs_pair_cmp(dir->head, lfs->root) == 0);
+
+    while (off > 0) {
+        int diff = lfs_min(dir->m.count - dir->id, off);
+        dir->id += diff;
+        dir->pos += diff;
+        off -= diff;
 
         if (dir->id == dir->m.count) {
             if (!dir->m.split) {
@@ -2080,6 +2088,8 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
                 LFS_TRACE("lfs_dir_seek -> %d", err);
                 return err;
             }
+
+            dir->id = 0;
         }
     }
 

tests/test_seek.sh

@@ -428,4 +428,78 @@ scripts/test.py << TEST
 TEST
 done
 
+echo "--- Root seek test ---"
+./scripts/test.py << TEST
+    lfs_mount(&lfs, &cfg) => 0;
+    for (int i = 3; i < $MEDIUMSIZE; i++) {
+        sprintf(path, "hi%03d", i);
+        lfs_mkdir(&lfs, path) => 0;
+    }
+
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    for (int i = 0; i < $MEDIUMSIZE; i++) {
+        if (i == 0) {
+            sprintf(path, ".");
+        } else if (i == 1) {
+            sprintf(path, "..");
+        } else if (i == 2) {
+            sprintf(path, "hello");
+        } else {
+            sprintf(path, "hi%03d", i);
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 1;
+        strcmp(path, info.name) => 0;
+    }
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+
+    for (int j = 0; j < $MEDIUMSIZE; j++) {
+        lfs_soff_t off = -1;
+
+        lfs_dir_open(&lfs, &dir, "/") => 0;
+        for (int i = 0; i < $MEDIUMSIZE; i++) {
+            if (i == 0) {
+                sprintf(path, ".");
+            } else if (i == 1) {
+                sprintf(path, "..");
+            } else if (i == 2) {
+                sprintf(path, "hello");
+            } else {
+                sprintf(path, "hi%03d", i);
+            }
+
+            if (i == j) {
+                off = lfs_dir_tell(&lfs, &dir);
+                off >= 0 => true;
+            }
+
+            lfs_dir_read(&lfs, &dir, &info) => 1;
+            strcmp(path, info.name) => 0;
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 0;
+        lfs_dir_close(&lfs, &dir) => 0;
+
+        lfs_dir_open(&lfs, &dir, "/") => 0;
+        lfs_dir_seek(&lfs, &dir, off) => 0;
+        for (int i = j; i < $MEDIUMSIZE; i++) {
+            if (i == 0) {
+                sprintf(path, ".");
+            } else if (i == 1) {
+                sprintf(path, "..");
+            } else if (i == 2) {
+                sprintf(path, "hello");
+            } else {
+                sprintf(path, "hi%03d", i);
+            }
+
+            lfs_dir_read(&lfs, &dir, &info) => 1;
+            strcmp(path, info.name) => 0;
+        }
+        lfs_dir_read(&lfs, &dir, &info) => 0;
+        lfs_dir_close(&lfs, &dir) => 0;
+    }
+
+    lfs_unmount(&lfs) => 0;
+TEST
+
 scripts/results.py